RU2755630C2 - Four-junction solar cell for space applications - Google Patents

Abstract

FIELD: solar energy.SUBSTANCE: multi-junction solar cell contains: substrate for growing; the first solar sub-cell formed over or in substrate for growing; changing intermediate layer deposited on the first solar sub-cell; and a set of layers of semiconductor material deposited over changing intermediate layer containing a set of solar sub-cells, including the second solar sub-cell located over and mismatched according to a lattice parameter relatively to substrate for growing and having width of forbidden zone in the range of 0.9-1.8 eV and at least upper solar sub-cell located over the second sub-cell and having aluminum content of more than 30% of mole fraction and width of forbidden zone in the range of 2.0-2.20 eV.EFFECT: invention provides for increased efficiency of photo conversion during operational service life of photoelectric power supply system and maximization of solar cell performance in working conditions.10 cl, 8 dwg

Description

The technical field to which the invention relates

[01] The present disclosure relates generally to solar cells and the manufacture of solar cells, and in particular to the design and determination of the composition and bandgap values of each of these four subcells in a solar cell with four junctions based on semiconductor compounds of III- Group V in order to achieve increased end-of-life performance that can be accurately determined for a given space mission and environment.

State of the art

[02] As used in this disclosure, the expression "bandgap" of a solar subcell, within which there are layers with different bandgap widths, should be understood as the bandgap of the solar subcell layer in which most of the charge carriers are generated (and such a sublayer is usually base p-type semiconductor layer of the base / emitter photoelectric junction of such a subcell). In the event that such a layer, in turn, has sublayers with different values of the band gap (for example, in the case of a base layer having a variable composition and, more specifically, a varying band gap), the sublayer of this solar subcell with the smallest value of the width The bandgap should be used as a definition of the "bandgap" of such a sub-element. In addition to the solar subcell, more generally in the case of a specially provided semiconductor region (such as a metamorphic layer), in which this semiconductor region has sublayers or subregions with different values of the band gap (for example, in the case of a semiconductor region having a variable composition and more specifically, the varying bandgap), sublayer or sub-region of this semiconductor region with the smallest value of the bandgap should be used as a definition of the "bandgap" of that semiconductor region.

[03] In recent years, mass production of multi-junction solar cells based on semiconductor compounds of Group III-V elements for space applications has accelerated the development of this technology. Compared to silicon solar cells, multi-junction solar cells based on semiconductor compounds of III-V elements have higher energy conversion efficiency and are generally more radiation resistant, although they tend to complicate the correct specification and manufacture. Typical commercial multi-junction solar cells based on Group III-V semiconductor compounds have energy efficiency in excess of 29.5% when illuminated by only one sun and zero air mass (AM0). The higher conversion efficiency of solar cells based on semiconductor compounds of Group III-V elements compared to silicon solar cells is partially based on the ability to achieve splitting of spectral lines of incident radiation through the use of a plurality of series-connected photovoltaic regions with different bandgap energies and the accumulation of electrical energy at a given voltage and current from each of the areas.

[04] In satellites and other space applications, the size, weight and cost of a satellite power system are directly related to the power and energy conversion efficiency of the solar cells used. In other words, the size of the payload and the availability of onboard services are proportional to the amount of power provided. Thus, as the payload becomes more complex, the amount of electricity consumed increases, and when planning space flights and applications for five, ten, twenty or more years, parameters related to the ratio of power to mass (W / kg), the ratio of power to area (W / m ² ) and efficiency during the entire service life of the solar cell. At the same time, interest is growing not only in the amount of electricity consumed per gram of mass and area occupied by a solar cell, not only during the initial deployment, but also throughout the entire service life of the satellite system, or, in terms of the design specification, in the amount of residual power delivered at a specified "end of life" (EOL), which is affected by radiation exposure of a solar cell over time in a particular space environment of an array of solar panels, with the EOL period differing for different space flight programs and applications.

[05] Typical solar cells based on semiconductor compounds of III-V elements are made on a semiconductor wafer in the form of vertical multi-junction structures or a series of superposed solar sub-cells, each sub-cell made with corresponding semiconductor layers and includes a photosensitive p-n junction. Each sub-element is designed to convert photons in all different spectral ranges or wavelengths into electrical current. Next, sunlight hits the front of the solar cell and photons pass through the subcells, with each subcell dedicated to photons in a specific wavelength range. After passing through a sub-element, photons that are not absorbed or converted into electrical energy fall on the next sub-elements, where it is assumed that such photons will be captured and converted into electrical energy.

[06] The sub-element closest to the incident sunlight is often referred to as the "extreme-top" or "top" sub-element, or in some terminology as the "first sub-element" and has the largest bandgap of all the sub-elements, with the sub-elements located below the first sub-item are called "second", "third", etc. sub-elements.

[07] Another terminology for defining sub-cells is based on the fact that a series of stacked solar sub-cells are epitaxially grown in series one after the other on a semiconductor substrate. In this case, the first subunit formed or grown on the substrate may be referred to as the "first" subunit, and subsequent subunits grown sequentially one after the other may be referred to as the "second", "third", and so on. sub-cells, such last sub-cells in the vertical arrangement being the "extreme top" or "top" sub-cells of the solar cell and have the largest band gap of all the sub-cells.

[08] A solar cell intended for use in a spacecraft (such as a satellite, space station or interplanetary spacecraft) has a number of sub-elements with compositions and bandgap values optimized to maximize energy conversion efficiency for the solar spectrum AM0 in outer space.

[09] The radiation resistance of a solar cell is determined by how well the cell performs its functions after being irradiated with radiation from particles of electrons or protons, which are characteristic of outer space. The standard metric is the ratio of end-of-life (or efficiency) performance to early-of-life (EOL / BOL) performance of a solar cell. EOL performance is a parameter of the cell performance after irradiating that test solar cell with a given electron or proton fluence (which may differ for different spaceflight programs or orbits). The performance of the BOL is the performance parameter before the exposure to particle radiation.

[10] One important mechanical or design consideration in the selection of semiconductor layers for a solar cell is the suitability of adjacent semiconductor layers in the solar cell, that is, each layer of crystalline semiconductor material that is deposited and grown to form a solar subcell has similar or substantially similar limitations or parameters of the crystal lattice.

[11] There are trade-offs between the inclusion of certain elements in the composition of the layer, which can lead to an increase in the voltage associated with such a sub-element, and therefore to potentially higher output power, as well as deviations from accurate lattice matching of adjacent layers due to the inclusion of such elements in the layer, which can lead to a higher probability of defects and, therefore, to a decrease in the yield of suitable products.

[12] In this regard, it should be noted that there is no strict definition of what is meant by the fact that two adjacent layers are "lattice matched" or "lattice mismatched". For the purposes of this disclosure, the term "lattice mismatched" refers to two adjacent materials or layers (greater than 100 nm thick) having lattice constants in the plane of the materials in their fully relaxed state that differ from each other in lattice constant by less than by 0.02%. (Applicant notes that this definition is significantly more stringent than what is proposed, for example, in US patent No. 8,962,993, which assumes a difference in lattice constant of less than 0.6% when determining the "lattice mismatched" layers) ...

[13] The traditional view over the years has been that in a monolithic two-stage solar cell "... the desired optical transmittance and current conductance between the top and bottom elements ... can be best achieved by lattice matching of the upper cell material with the lower cell material Lattice mismatch leads to the formation of defects or dislocations in the crystal lattice, where recombination centers can arise, causing the loss of photogenerated minority carriers and thereby significantly degrading the photoelectric quality of the device. , short circuit current (Jsc) and duty cycle (FF), which represents the ratio or balance between current and voltage to obtain effective power "(Jerry M. Olson, US Patent No. 4,667,059," Current and Lattice Matched Tandem Solar Cell ").

[14] As progress has been made with high-efficiency multi-junction solar cells with four or more subcells, however, “it is generally accepted that substantially lattice-matched designs are desirable because they have proven reliability and use less semiconductor material. than metamorphic solar cells, which require relatively thick buffer layers to account for differences in lattice constants of different materials "(Rebecca Elizabeth Jones - Albertus et al., US Patent No. 8,962,993).

[15] This disclosure presents design features of multijunction solar cells that deviate from this traditional concept in order to improve the efficiency of a multijunction solar cell when converting solar energy (or photons) to electrical energy and optimize such efficiency at the "end of life".

Brief Description of Drawings

Disclosure tasks

[16] An object of the present disclosure is to provide improved photoconversion efficiency in a multi-junction solar cell for space applications during the operational life of a photovoltaic power supply system.

[17] Another object of the present disclosure is to provide a multi-junction solar cell in which the composition of the sub-cells and their bandgap values are configured to maximize the efficiency of the solar cell under operating conditions at a given high temperature (particularly in the range 40-70 degrees Celsius) when deployed in space with a solar spectrum assuming only one sun AM0 at a given time (EOL) after initial deployment, which time period may be at least one, five, ten, fifteen, or twenty years and not maximized during initial deployment (BOL).

[18] Another object of the present invention is to provide a solar cell with four junctions in which the average band gap of all four elements, that is, the sum of the four bandgap values of each subcell divided by four, is greater than 1.35 eV ...

[19] Another object of the present invention is to provide a solar cell with four junctions, in which the lower two sub-cells are lattice mismatched, and in which the current flowing through the lower sub-cell is deliberately calculated to be substantially greater than the current flowing through the top three sub-elements when measured at "start of life" or during initial deployment.

[20] Some implementations of the present disclosure may include or implement fewer aspects and features identified in the above objectives.

Signs of invention

[21] All ranges of numerical parameters set forth in this disclosure are to be understood as encompassing any and all sub-ranges or "intermediate generalizations" included therein. For example, the specified range of "1.0-2.0 eV" for the bandgap value should be considered to include any and all sub-bands from a minimum value of 1.0 eV or more to a maximum value of 2.0 eV or less. , for example, 1.0-1.2, or 1.3-1.4 or 1.5-1.9 eV.

[22] Briefly and generally, the present disclosure provides a multi-junction solar cell comprising: a growth substrate; a first solar sub-cell (D) formed on top of or in the growth substrate; a variable intermediate layer deposited over the first solar subcell; and a plurality of layers of semiconductor material deposited on top of a variable intermediate layer containing a plurality of solar subcells, including a second solar subcell (C) located on top and lattice mismatched with the growth substrate and having a band gap in the range 0.9-1 , 8 eV, and at least an upper solar sub-element (A) located on top of the second sub-element and having an aluminum content of more than 30% mole fraction and a band gap in the range of 2.0-2.20 eV; where the changing intermediate layer changes in its composition to match the lattice parameter of the substrate for growing on one side and the second solar subcell on the other side and consists of any of the semiconductor compounds of III-V groups based on As, P, N, Sb, taking into account the limitations associated with the fact that its lattice parameter in the plane throughout its entire thickness must be greater than or equal to the lattice parameter in the plane of the substrate for growing; where the combination of compositions and bandgap values of solar subcells is intended to maximize the efficiency of the solar cell at a given time after initial deployment, when the solar cell is deployed in space at AM0, with a 1 MeV electron transfer equivalent to a fluence of at least 5 × 10 ¹⁴ e / cm ² , and at an operating temperature in the range of 40-70 degrees Celsius, while the target time is at least five years and is referred to as end of life (EOL).

[23] It should be noted that in this sequence of solar sub-cell placement, the listing provides at least three sub-cells, assuming that the multi-junction solar cell may be a multi-junction solar cell with three junctions, four junctions, five junctions, or more junctions.

[24] In another aspect (and using alternative terminology to define and prioritize the "first", "second", "third" and "fourth" subelements A, B, C and D, respectively, than those used in the previous paragraphs ), the present disclosure provides a four-junction solar cell comprising an upper first solar sub-cell (A) composed of a semiconductor material having a first band gap; a second solar sub-cell (B) adjacent to said first solar sub-cell and consisting of a semiconductor material having a second bandgap that is less than the first bandgap and lattice-matched with the upper first solar sub-cell; a third solar sub-cell (C) adjacent to said second solar sub-cell and consisting of a semiconductor material having a third bandgap that is less than the second bandgap and lattice-matched with the second solar sub-cell; and a fourth or lower solar sub-cell (D) adjacent to said third solar sub-cell and consisting of a semiconductor material having a fourth band gap that is less than a third band gap; where the average band gap of all four subelements (that is, the sum of the four bandgap values of each subelement divided by four) is greater than 1.35 eV.

[25] In another aspect, the present disclosure provides a four-junction solar cell suitable for use in space conditions and designed to operate at AM0 and 1 MeV electron transfer, equivalent to a fluence of at least 1 × 10 ¹⁴ e / cm ² , and the solar cell contains subcells in which the combination of compositions and the bandgap value of the subcells is intended to maximize the efficiency of the solar cell at a given time after initial deployment, when the solar cell is deployed in space, at an operating temperature in the range of 40-70 degrees Celsius, with a given the time period is at least five years and is referred to as "end of life" (EOL). More specifically, the solar cell comprises: an upper first solar sub-cell (A) composed of aluminum-indium-gallium phosphide and having a first band gap in the range of 2.0-2.2 eV; a second solar sub-cell (B) adjacent to said first solar sub-cell and comprising an emitter layer composed of indium-gallium phosphide or aluminum-indium-gallium arsenide and a base layer composed of aluminum-indium-gallium arsenide having a second width a bandgap in the range of approximately 1.55-1.8 eV and matched in lattice parameter with the upper first solar subcell, and the emitter and base layers of the second solar subcell form a photovoltaic junction; a third solar sub-cell (C) adjacent to said second solar sub-cell, composed of indium-gallium arsenide, having a third bandgap smaller than that of the second solar sub-cell, and lattice-matched with the second solar sub-cell; and a fourth or lower solar sub-element (D) adjacent to said third solar sub-element, consisting of germanium and having a fourth band gap of about 0.67 eV; where the average band gap of the solar cell (that is, the average number or numerical sum of the band gap values of each of the four subcells divided by four) is equal to or greater than 1.35 eV.

[26] In some embodiments, the fourth sub-element is germanium.

[27] In some embodiments, the second sub-element has a band gap of about 1.73 eV, and the upper first solar sub-element has a band gap of about 2.10 eV.

[28] In some embodiments, the upper first solar subcell has a band gap of about 2.05-2.10 eV, the second solar subcell has a band gap in the range of 1.55-1.73 eV; and the third solar sub-element has a bandgap in the range of 1.15-1.41 eV.

[29] In some embodiments, the upper first solar subcell has a band gap of about 2.10, the second solar subcell has a band gap of about 1.73 eV; and the third solar subcell has a bandgap in the 1.41 eV range.

[30] In some embodiments, the upper first solar subcell has a band gap of about 2.10, the second solar subcell has a band gap of about 1.65 eV; and the third solar subcell has a band gap of 1.3 eV.

[31] In some embodiments, the upper first solar subcell has a band gap of about 2.05, the second solar subcell has a band gap of about 1.55 eV; and the third solar subcell has a band gap of 1.2 eV.

[32] In some embodiments, the first solar subcell has a bandgap of 2.05 eV.

[33] In some embodiments, the implementation of the bandgap of the third solar subcell is less than 1.41 eV and greater for the fourth subcell.

[34] In some embodiments, the third solar subcell has a bandgap in the range of 1.15 to 1.35 eV.

[35] In some embodiments, the third solar subcell has a bandgap in the range of 1.1-1.2 eV.

[36] In some embodiments, the third solar subcell has a band gap of approximately 1.2 eV.

[37] In some embodiments, the upper first solar sub-cell consists of aluminum-indium-gallium phosphide; the second solar sub-cell includes an emitter layer composed of indium-gallium phosphide or aluminum-indium-gallium arsenide and a base layer composed of aluminum-indium-gallium arsenide; the third solar sub-element consists of indium-gallium arsenide; and the fourth sub-element is germanium.

[38] In some embodiments, a distributed Bragg reflector (DBR) layer is further provided adjacent and between the third and fourth or lower solar subcell and positioned so that light can penetrate and pass through the third solar subcell and at least a portion of the light could be reflected back into the third solar sub-element from the DBR layer.

[39] In some embodiments, the DBR layer is composed of a plurality of alternating layers of lattice matched materials with an abrupt change in their respective refractive indices.

[40] In some embodiments, the refractive index difference between the alternating layers of the DBR layer is maximized to minimize the number of periods required to achieve a given reflectance, and the thickness and refractive index of each period determine the stop band and its ultimate wavelength.

[41] In some embodiments, the DBR layer includes a first DBR layer composed of a plurality of _{p-type In z} Al _x Ga _1-xz As sublayers, and a second DBR layer located on top of the first DBR layer and composed of a plurality of In _{w sublayers} Al _y Ga _1-yx As p-type, where 0 <x <1, 0 <y <1, 0 <z <1, and y is greater than x, therefore the first and second DBR layers differ in their composition, thereby increasing the width bandwidth when reflecting the DBR layer.

[42] In some embodiments, the implementation of the choice of the composition of the subcells and their bandgap values maximizes efficiency at high temperature (in the range of 40-70 degrees Celsius) when deployed in space at a given time after the initial deployment (which is referred to as the start of life or ( BOL)), and this predetermined time is referred to as end of life (EOL) and is at least five years.

[43] In some embodiments, the uppermost or upper first solar subcell consists of a base layer (In _x Ga _1-x ) _1-y Al _y P, where x is 0.505 and y is 0.142, which corresponds to a band gap of 2, 10 eV, and the emitter layer (In _x Ga _1-x ) _1-y Al _y P, where x is 0.505 and y is 0.107, which corresponds to a band gap of 2.05 eV.

[44] In some embodiments, an interlayer (or "variable interlayer") is further provided between the third sub-element and the fourth sub-element or bottom sub-element, the intermediate layer being varied in composition to match the lattice parameter of the third solar sub-cell on one side, and the fourth or lower solar subcell on the other hand and consists of any of the semiconductor compounds of Group III-V elements based on As, P, N, Sb, taking into account the restrictions associated with the fact that the lattice parameter in the plane must be greater than or equal to the lattice parameter in plane of the fourth or lower solar sub-element, and the energy of the forbidden zone must be greater than that of the fourth solar sub-element.

[45] In some embodiments, the intermediate layer (or "variable intermediate layer") is stepped in composition from one to four hops to match the lattice parameter of the third solar subcell on one side and the fourth or lower solar subcell on the other side and consists of In _x Ga _1-x As or (In _x Ga _1-x ) _y Al _1-y As, where 0 <x <1, 0 <y <1, and x and y are selected so that the band gap is in the range of 1.15-1.41 eV throughout its thickness.

[46] In some embodiments, the variable interlayer has a constant band gap in the range of 1.15-1.41 eV, 1.2-1.35 eV, or 1.25-1.30 eV.

[47] In some embodiments, any of 1) the emitter layer or 2) the base layer and the emitter layer of the upper first solar subcell has a lattice constant that differs from the lattice constant of the second solar subcell.

[48] In some embodiments, each sub-element includes an emitter region and a base region, and one or more of the extreme top or top-most sub-elements have a base region having a doping ramp that increases exponentially from 1 × 10 ¹⁵ atoms per cubic centimeter in the region adjacent to the pn junction, up to 4 × 10 ¹⁸ atoms per cubic centimeter in the region adjacent to the adjacent layer on the back side of the base region, and the emitter region having a gradual change in doping, which decreases from approximately 5 × 10 ¹⁸ atoms per cubic centimeter in the emitter region immediately adjacent to the adjacent sub-element layer, up to 5 × 10 ¹⁷ atoms per cubic centimeter in the emitter region adjacent to the pn junction.

[49] In some embodiments, at least one of the outermost upper sublayers of the variable intermediate layer has a higher lattice constant than adjacent semiconductor body layers in the upper sublayer of the variable intermediate layer located on top of the variable intermediate layer.

[50] In some embodiments, the lattice constant difference between adjacent third and fourth or lower sub-elements is in the range of 0.1-0.2 Angstrom.

[51] In some embodiments, a first threading dislocation suppression layer is further provided having a thickness in the range of 0.10-1.0 microns and located above said fourth or lower solar subcell and below the variable interlayer.

[52] In some embodiments, a second threading dislocation suppression layer having a thickness in the range of 0.10-1.0 microns and composed of InGa (Al) P is further provided, the second threading dislocation suppression layer being disposed over and directly adjacent to said varying interlayer to reduce the propagation of threading dislocations, wherein said second threading dislocation suppression layer has a composition that is different from the composition of the first threading dislocation suppression layer and differs from the adjacent variable interlayer.

[53] In another aspect, the present disclosure provides a method of manufacturing a four-junction solar cell, comprising: providing a germanium substrate defining a first sub-cell; growing a series of semiconductor material layers on a germanium substrate using a semiconductor deposition process to form a solar cell containing a plurality of sub-cells, including a second sub-cell located on top of the germanium substrate, lattice mismatched with it and having a band gap of 1.41 eV or less, third a sub-element located on top of the second sub-element and having a bandgap in the range of about 1.55-1.8 eV, and an upper sub-element located on top of the third sub-element and having a band gap in the range of 2.0-2.15 eV.

[54] In some embodiments, one or more additional layers may be added or removed in the element structure without departing from the scope of this disclosure.

[55] Some implementations of the present disclosure may include or implement fewer aspects and features identified in the foregoing Summary.

Brief Description of Drawings

[56] The invention will be better understood by reference to the following detailed description, when considered in conjunction with the accompanying drawings, in which:

[57] Figure 1 is a graph representing the BOL values of the parameter Eg / q - Voc at 28 ° C plotted against the bandgap of some two-component materials defined along the X-axis;

[58] FIG. 2 is a cross-sectional view of a solar cell of a first embodiment of a four-junction solar cell after several manufacturing steps, including depositing some semiconductor layers on a substrate to grow to a contact layer according to the present disclosure;

[59] Figure 3 is a plot of the doping profile in the base and emitter layers of a subcell in a solar cell according to the present disclosure;

[60] FIG. 4A is a cross-sectional view of a second embodiment of a four-junction solar cell after several manufacturing steps including growing some semiconductor layers on a growth substrate to a contact layer according to the present disclosure;

[61] FIG. 4B is a cross-sectional view of a third embodiment of a four-junction solar cell after several manufacturing steps including growing some semiconductor layers on a growth substrate to a contact layer according to the present disclosure;

[62] Figure 5 is a cross-sectional view of a fourth embodiment of a four-junction solar cell after several manufacturing steps including growing some semiconductor layers on a growth substrate to a contact layer according to the present disclosure;

[63] Figure 6 is a cross-sectional view of a solar cell of the present disclosure as implemented in a CIC and mounted on a panel;

[64] FIG. 7 is a graph representing the bandgap of some bicomponent materials and their lattice constants; and

[65] Fig. 8 is an enlarged view of a portion of the graph (Fig. 7) illustrating various GaInAs and GaInP compounds with different proportions of gallium and indium and the location of specific compounds in the graph.

Detailed description of the invention

[66] A number of different features of multi-junction solar cells are disclosed in the applicant's related applications. Some, many, or all of such features may be incorporated into the structures and processes associated with "vertical" metamorphic multi-junction solar cells of the present disclosure. More specifically, however, the present disclosure is directed to fabricating a multi-junction solar cell grown on a single growth substrate including, in one embodiment, two lower sub-cells, that is, the fourth and third sub-cells are lattice matched. However, in some embodiments, the implementation of the present disclosure relates more specifically to solar cells with four transitions with bandgaps with direct transitions in the range of 2.0-2.15 eV (or higher) for the upper first subcell and 1) 1.65-1 , 8 eV and 2) 1.41 eV or less for the second and third sub-elements, respectively, and forbidden bands with indirect transitions of 0.6-0.8 eV for the lower fourth sub-element.

[67] The present disclosure provides an unconventional four-junction structure (with three lattice-matched grown subcells lattice-matched to the fourth or bottom Ge substrate) resulting in an unexpectedly significant performance improvement over a conventional solar cell. with three junctions, despite the fact that there is a significant current mismatch between the upper three junctions and the lower Ge junction, that is, the fourth subelement. This performance improvement is especially realized at high temperature and after high exposure to cosmic radiation by the proposal to include semiconductors with high bandgap values, which are inherently more resistant to radiation and temperature, thereby specifically addressing the problem of ensuring continuous adequate efficiency and output power during the entire operational flight and especially at the "end of life".

[68] Another method characterizing the present disclosure is that in some embodiments of a four-junction solar cell, the average bandgap of all four subcells (i.e., the sum of the four bandgaps of each subcell divided by four) is greater than 1 , 35 eV.

[69] In some embodiments, the fourth sub-element is germanium, while in other embodiments, the fourth sub-element is InGaAs, GaAsSb, InAsP, InAlAs, or SiGeSn, InGaAsN, INGaAsNSb, INGaAsNBi, InGaAsNSbBi, InGaBiN, InGaAsNSbBi, InGaSbN, InSbN based on compounds of elements of III-V or II-VI groups.

[70] Another descriptive aspect of the present disclosure is to characterize the fourth sub-element or bottom sub-element as having a direct transition bandgap greater than 0.75 eV.

[71] The band gap with indirect transitions in germanium at room temperature is approximately 0.66 eV, while the band gap with direct transitions in germanium at room temperature is 0.8 eV. Those of ordinary skill in the art will usually indicate a 0.67 eV "band gap" for germanium because it is lower than the forward band gap of 0.8 eV.

[72] Thus, the reference to "the fourth or lower subelement has a bandgap with direct transitions greater than 0.75 eV" clearly implies the inclusion of germanium as a possible semiconductor for the fourth or lower subelement, although equally well other semiconductor material can also be used.

[73] More specifically, the present disclosure provides a relatively simple and reproducible technology that does not use the inverted processing associated with the manufacture of inverted metamorphic multijunction solar cells, and is suitable for use in high-volume production environments in which different semiconductor layers are grown on a substrate for growing in the MOCVD reactor, and subsequent processing steps are defined and selected to minimize any physical damage to the quality of the deposited layers, thereby providing a relatively high yield of operable solar cells that meet the technical requirements for the completion of manufacturing processes.

[74] As suggested above, additional improvements in the design of multijunction solar cells are being made to address the challenges posed by the wide variety of requirements for new space programs and applications. Moreover, while such improvements may represent relatively small quantitative changes in the composition or band gap of some sub-elements, such small parametric changes (for example, from 0.1 to 0.5 eV in specific values of the band gap of the upper first sub-element or the third sub-element ) provide significant efficiency improvements that, in particular, solve the "problems" that have been found with existing modern commercial multi-junction solar cells, and provide a "solution" that represents an "inventive step" in the design process.

[75] One aspect of the present disclosure relates to the use of aluminum in active layers of top subcells in a multijunction solar cell. The effects of increasing the amount of aluminum as a constituent element in the active layer of the sub-cell affect the performance of the photovoltaic device. One criterion for "quality" or "perfection" of a solar cell junction is the difference between the band gap of the semiconductor material in that subcell or junction and the voltage Voc or open circuit voltage of the same junction. The smaller the difference, the higher the Voc of the solar cell junction relative to the bandgap and the higher the performance of the device. The Voc voltage is very sensitive to the quality of the semiconductor material, therefore, the lower the Eg / q - Voc of a device, the higher the quality of the material in that device. There is a theoretical limit for this difference known as the Shockley-Quaisser limit. It is very good that the junction of a solar cell can be at a given concentration of light and a given temperature.

[76] Experimental data obtained for solar cells with one transition based on (Al) GaInP show that an increase in the Al content in this transition (corresponding to the uppermost or uppermost subcell) leads to a larger difference Voc - Eg / q, which indicates the fact that the quality of the material of the joint decreases with an increase in the Al content. Figure 1 shows this effect. All three compositions shown in the figure are lattice-matched with GaAs, but have a different Al composition. The addition of Al increases the band gap of the transition, but this also increases Voc - Eg / q. Therefore, it can be concluded that the addition of Al to the semiconductor material degrades this material in such a way that a solar cell device made of this material does not work as well as a junction with less Al.

[77] Referring to the multi-junction solar cell arrangement of the present disclosure, FIG. 2 is a cross-sectional view of a first embodiment of a four-junction solar cell 200 after several manufacturing steps including growing some semiconductor layers on a growth substrate to a contact layer 322 according to this disclosure.

[78] As shown in FIG. 2 in the illustrated example, the fourth or lower sub-element D includes a growth substrate 300 formed of p-type germanium ("Ge") which also serves as a base layer. A rear metal contact pad 350 formed on the bottom of the base layer 300 provides electrical contact with the multi-junction solar cell 200. The bottom sub-cell D further includes, for example, a highly doped n-type Ge emitter layer 301 and an indium arsenide nucleus layer 302. gallium ("InGaAs") n-type. A seed layer is deposited on top of the base layer, and an emitter layer is formed in the substrate by diffusion of dopants into the Ge substrate, thereby forming an n-type Ge layer 301. Highly doped p-type aluminum gallium arsenide ("AlGaAs") and n-type heavily doped gallium arsenide ("GaAs") layers 304, 303 can be deposited over the seed layer to provide a low impedance path between the lower fourth subcell and the third sub-element.

[79] In some embodiments, distributed Bragg reflector (DBR) layers 305 are then grown adjacent to and located between the tunnel diode 303, 304 of the lower fourth sub-cell D and the third solar sub-cell C. The DBR layers 305 are placed so that light can penetrate and pass through the third solar sub-element C, and at least part of it could be reflected back into the third solar sub-element C from the layers 305 DBR. In the embodiment shown in FIG. 2, DBR layers 305 are specially positioned between the third solar subcell C and the tunnel diode layers 304, 303; in other embodiments, distributed Bragg reflector (DBR) layers may be sandwiched between tunnel diode layers 304/303 and buffer layer 302.

[80] In some embodiments, the distributed Bragg reflector (DBR) layers 305 may be composed of a plurality of alternating grating-matched materials 305a-305z layers with a hopping change in their respective refractive indices. In some embodiments, the refractive index difference between the alternating layers is maximized in order to minimize the number of periods required to achieve a given reflectance, and the thickness and refractive index of each period determine the stop band and its ultimate wavelength.

[81] In some embodiments, the distributed Bragg reflector (DBR) layers 305a-305z include a first DBR layer composed of a plurality of _{p-type In z} Al _x Ga _1-xz As layers and a second DBR layer overlaid on the first layer DBR and consisting of a plurality of layers In _w Al _y Ga _1-yw As p-type, where 0 <w <1, 0 <x <1, 0 <y <1, 0 <z <1, and y is greater than x.

[82] Although the present disclosure shows a DBR layer 305 located between the third and fourth sub-elements, in other embodiments, the DBR layers may be located between the first and second sub-elements, and / or between the second and third sub-elements and / or between the third and fourth sub-elements. ...

[83] In the illustrated example shown in FIG. 2, the third sub-element C includes a high-doped back surface field ("BSF") layer 306 based on indium gallium arsenide ("AlInGaAs") p-type, base layer 307 InGaAs p-type, high-doped emitter layer 308 of indium-gallium arsenide ("InGaAs") n-type and high-doped window layer 309 based on aluminum-indium phosphide ("AlInP2") n-type or gallium-indium phosphide ("GaInP" ). The InGaAs base layer 307 of subcell C may include, for example, about 1.5% In. You can also use other formulations. The base layer 307 is formed on top of the BSF layer 306 after the BSF layer is deposited on top of the DBR layers 305.

[84] The window layer 309 is deposited on the emitter layer 308 of the third sub-element C. The window layer 309 in the third sub-element C also helps to reduce recombination losses and improves the passivation of the element surface of the junctions below. Tunnel junction layers 310, 311 of heavily doped n-type InGaP and p-type AlGaAs (or other suitable compositions) can be deposited over sub-element C prior to deposition of sub-element B layers.

[85] The second sub-element B includes a p-type aluminum-gallium-indium arsenide ("AlInGaAs") high doped back surface field ("BSF") layer 312, p-type AlInGaAs base layer 313, high doped phosphide layer 314 indium-gallium ("InGaP2") or n-type AlInGaAs and a high-alloyed n-type aluminum-indium-gallium phosphide ("AlGaAlP") window layer 315. The emitter layer 314 InGaP of the second sub-element B may include, for example, about 50% In. You can also use other formulations.

[86] Heavily doped layers 316, 317 of n-type InGaP and p-type AlGaAs tunnel junctions can be deposited on the second sub-element B prior to the deposition of layers of the upper first sub-element A.

[87] In the illustrated example, the uppermost or uppermost first sub-element includes a high doped p-type aluminum phosphide ("InAlP2") layer 318 BSF, a p-type InGaAlP base layer 319, a high-doped n-type InGaAlP emitter layer 320 and a highly doped n-type InAlP2 window layer 321. The base layer 319 of the first sub-element is deposited on top of the BSF layer 318 after the BSF layer 318 is formed.

[88] After deposition of the top protective or contact layer 322, the grid lines are formed by evaporation, lithographic drawing, and deposited over the top protective or contact layer 322.

[89] In some embodiments, at least the base of at least one of the first, second, or third solar subcells has a varying doping profile, that is, the doping level varies from one surface to another throughout the thickness of the base layer. In some embodiments, the doping fade is exponential. In some embodiments, the doping fade is incremental and monotonic.

[90] In some embodiments, the emitter of at least one of the second, third, or fourth solar subcells (C, B, or A, respectively) also has a variable doping profile, that is, the doping level varies from one surface to another throughout the thickness of the emitter layer ... In some embodiments, the doping fade decreases linearly or monotonically.

[91] As a specific example, Fig. 3 shows the doping profile of the emitter and base layers, which depicts the amount of dopant in the emitter region and the base region of the subcell. N-type dopants include silicon, selenium, sulfur, germanium, or tin. P-type dopants include silicon, zinc, chromium, or germanium.

[92] As shown in the example of FIG. 3, in some embodiments, one or more sub-elements (C, B, or A) have a base region having a doping fade that increases from a value in the range of 1 x 10 ^{15 -} 1 x 10 ¹⁸ free carriers per cubic centimeter in the region adjacent to the pn junction, up to a value in the range of 1 × 10 ^{16 -} 4 × 10 ¹⁸ free carriers per cubic centimeter in the region adjacent to the adjacent layer from the back of the base, and an emitter region that has gradual change in doping, which decreases from a value in the range of approximately 5 × 10 ^{18 -} 1 × 10 ¹⁷ free carriers per cubic centimeter in the region immediately adjacent to the adjacent layer, to a value in the range of 5 × 10 ^{15 -} 1 × 10 ¹⁸ free carriers per cubic centimeter cubic centimeter in the area adjacent to the pn junction.

[93] The bold lines 612 and 613 shown in FIG. 3 illustrate one embodiment of base doping having an exponential change and the emitter doping being linear.

[94] Thus, the doping level over the entire thickness of the base layer can vary exponentially in the range from 1 × 10 ¹⁶ free carriers per cubic centimeter to 1 × 10 ¹⁸ free carriers per cubic centimeter, as represented by curve 613 depicted in the figure.

[95] Similarly, the doping level across the entire thickness of the emitter layer can decrease linearly from 5 × 10 ¹⁸ free carriers per cubic centimeter to 5 × 10 ¹⁷ free carriers per cubic centimeter, as represented by curve 612 in the figure.

[96] The absolute value of the collection field generated by the exponential doping gradient exp [-x / λ] is given by a constant electric field with an amplitude E = kT / q (1 / λ)) (exp [-xb / λ]), where k is Boltzmann's constant, T is the absolute temperature in degrees Kelvin, q is the absolute value of the electronic change, and λ is the parameter of the gradual decrease in the doping level.

[97] The effectiveness of an embodiment of the present doping distribution disclosure was demonstrated in a test solar cell that included an exponential doping profile in a subcell with a three micron base layer according to one embodiment.

[98] The exponential doping profile proposed in one embodiment of the present disclosure creates a constant field in the doped region. In the particular multi-junction solar cell materials and structure of the present disclosure, the lower subcell has the lowest short circuit current of all subcells. Since in a multi-junction solar cell, the individual sub-cells are stacked on top of each other and form a series circuit, the total current flowing in the entire solar cell is thus limited by the smallest current generated in any of the sub-cells. Thus, with an increase in the short-circuit current in the lower element, the current closely approaches the current of the sub-elements located above, and the overall efficiency of the solar cell also increases. In a multi-junction solar cell with increased efficiency, the implementation of this arrangement of alloying will lead to an increase in efficiency. In addition to increasing efficiency, the collection field created by the exponential doping profile will increase the radiation resistance of the solar cell, which is important for spacecraft applications.

[99] While the exponentially doped profile is a doping design that has been implemented and tested, other doping profiles can result in a ramping collection field that may provide other benefits. For example, a different doping profile could create a linear field in the doped region that would be beneficial for both minority carrier collection and end-of-life (EOL) radiation resistance of the solar cell. Such other doping profiles in one or more base layers are within the scope of this disclosure.

[100] The doping profile depicted herein is merely illustrative and other more complex profiles may be used as will be apparent to those skilled in the art without departing from the scope of the present invention.

[101] FIG. 4A is a cross-sectional view of a second embodiment of a four junction solar cell 400 after several manufacturing steps including growing some semiconductor layers on a growth substrate to a contact layer 322 with various subcells similar to the structure described and depicted in Fig. 2. For the sake of brevity, the description of layers 350, 300-304, and 306-322 will not be repeated here.

[102] In the embodiment shown in FIG. 4A, a variable intermediate layer 505 comprising, in one embodiment, progressive sublayers 505a-505z is disposed on top of the tunnel diode layer 304. In particular, the varying intermediate layer provides a transition from the lattice constant of the substrate to a higher value of the lattice constant of the second, third and fourth sub-elements.

[103] A first layer 504 of "alpha" or threading dislocation suppression, preferably consisting of p-type InGaP, is deposited over the tunnel diode 303/304 to a thickness of 0.10 to about 1.0 microns. Such an alpha layer is designed to suppress the propagation of threading dislocations in the opposite direction of growth in the first subunit D, or in the direction of growth in the second subunit C, and is described in more detail in US Patent Application Publication No. 2009/0078309 A1 (Cornfeld et al. ). More generally, the alpha layer has a different composition than the adjacent layers above and below it. As shown in FIG. 4A, the stepped line on the left depicts a stepping change in the lattice constant in the plane, which gradually increases from sublayer 505a to sublayer 505z, such sublayers being completely unrelaxed.

[104] The metamorphic layer (or changing interlayer) 505 is deposited on top of the alpha layer 504 using a surfactant. Layer 505 is preferably a compositionally stepped series of p-type InGaAs or InGaAlAs layers, preferably with a monotonically varying lattice constant, so as to achieve a gradual lattice constant transition in the semiconductor structure from the fourth sub-element D to the third sub-element C while minimizing the occurrence of threading dislocations ... In one embodiment, the band gap of the layer 505 is constant throughout its thickness, preferably about 1.22 to 1.34 eV, or otherwise matched with a value slightly greater than the band gap of the third sub-element C. In another embodiment, the band gap the sublayers of layer 505 range from 1.22 to 1.34 eV, with the first layer having a relatively high bandgap and subsequent layers having gradually decreasing bandgaps. In one embodiment, the variable interlayer can also be thought of as consisting of In _x Ga _1-x As, where 0 <x <1, 0 <y <1, and x and y are selected such that the band gap of the interlayer remains constant in the range of about 1.22-1.34 eV or was equal to another suitable value of the band gap.

[105] In one embodiment, aluminum is added to one sublayer to make one particular sublayer harder than another, thereby causing dislocations in the softer material.

[106] When growing the metamorphic intermediate variable layer 505 with a surfactant, a suitable chemical is introduced into the reactor during the growth of the layer 505 to improve the characteristics of the surface of the layer. In a preferred embodiment, such an element may be a dopant or donor atom such as selenium (Se) or tellurium (Te). Therefore, small amounts of Se or Te are included in the metamorphic layer 406 and remain in the finished solar cell. Although Se or Te are preferred n-type dopant atoms, other non-isoelectronic surfactants can also be used.

[107] Surfactant-induced growth results in a significantly smoother or planarized surface. Since the geometry of the surface affects the bulk properties of the semiconductor material as it grows and the layer becomes thicker, the use of surfactants minimizes intergrowth dislocations in the active regions, thereby increasing the overall efficiency of the solar cell.

[108] As an alternative to using a non-electronic surfactant, an isoelectronic surfactant can be used. The term "isoelectronic" refers to surfactants such as antimony (Sb) or bismuth (Bi), since such elements have the same number of valence electrons as the P atom of InGaP or the As atom in InGaAlAs in the metamorphic buffer layer. Such Sb or Bi surfactants will typically not be present in the metamorphic layer 505.

[109] In one embodiment of the present disclosure, the metamorphic layer 505 consists of a plurality of InGaAs layers with a monotonically varying lattice constant, each layer having a band gap in the range of 1.22-1.34 eV. In some embodiments, the bandgap is constant in the range 1.27-1.31 eV throughout the thickness of layer 505. In some embodiments, the constant bandgap is in the range 1.28-1.29 eV.

[110] An advantage of using a constant band gap material such as InGaAs is that the arsenide-based semiconductor material is much easier to process in standard commercial MOCVD reactors.

[111] While the described embodiment of the present disclosure uses a plurality of InGaAs layers for the metamorphic layer 505 for reasons of manufacturability and transparency to radiation, other embodiments of the present disclosure may use various material systems to achieve a lattice constant change from the second sub-element C to the first sub-element D. In other embodiments of the present disclosure, continuously changing materials can be used as opposed to stepping materials. More generally, the changing intermediate layer can consist of any of the semiconductor compounds of Group III-V elements based on As, P, N, Sb, taking into account the limitations associated with the fact that the in-plane lattice parameter should be less than or equal to the lattice parameter in plane of the third sub-element C and is greater than or equal to the lattice parameter in the plane of the fourth sub-element D. In some embodiments, the layer 505 has a bandgap energy greater than that of the third sub-element C and in other embodiments has a band gap energy that is less than that of the third sub-element C.

[112] In some embodiments, a second "alpha" or threading suppression layer 507, preferably consisting of p-type GaInP, is deposited over a metamorphic buffer layer 505 with a thickness of 0.10 to about 1.0 microns. This alpha layer is designed to prevent the propagation of threading dislocations either in the opposite direction of growth in the first subunit D or in the direction of growth in the second subunit C and is described in more detail in US Patent Application No. 2009/0078309 A1 (Cornfeld et al.) ...

[113] In the embodiment shown in FIG. 4B, a variable intermediate layer 506 including, in one embodiment, stepped sublayers 505a-505zz, is disposed on top of the tunnel diode layer 304. In particular, the varying intermediate layer allows the lattice constant to change from the lattice constant of the substrate and the first solar sub-cell to a higher value of the lattice constant of the second, third and fourth sub-elements C, B and A and differs from the embodiment shown in FIG. 4A only in that that the uppermost or uppermost sublayer 505zz of the changing intermediate layer 506 is relaxed or only partially unrelaxed (as opposed to the completely unrelaxed layers below it), since it has a lattice constant greater than the lattice constant of the layer located above it, that is, alpha - layer 507 (should be the second alpha layer) or layer 306 BSF. In short, in this embodiment, there is a "slip" of the varying layers as depicted on the left side of FIG. 4B, which shows that the grating constant step increases from layer 505a to layer 505zz.

[114] Figure 5 is a cross-sectional view of a fourth embodiment of a four-junction solar cell 500 after several manufacturing steps, including growing some semiconductor layers on a growth substrate to a contact layer 322, with various sub-elements similar to the structure described and depicted. in Figures 2, 4A and 4B.

[115] In this embodiment, both the intermediate variable layer and the DBR layer are located between the third subunit C and the fourth subunit D. Layers 450, 400-404, 504-507, and 305-322 are substantially similar to those shown in FIG. 2 and 4A or 4B, and their description need not be repeated here.

[116] In this embodiment, distributed Bragg reflector (DBR) layers 305 are grown adjacent to and on top of the alpha layer 507 (or metamorphic buffer layer 506 if layer 507 is missing). The DBR layers 305 are placed so that light can enter and pass through the third solar sub-element C and at least a portion of it can be reflected back into the third sub-element C from the DBR layers 305. In the embodiment depicted in FIG. 5, distributed Bragg reflector (DBR) layers 305 are specifically positioned between the third sub-element C and the metamorphic layer 506.

[117] In some embodiments, the distributed Bragg reflector (DBR) layers 305 may be comprised of a plurality of alternating grating-matched layers 305a-305z of their respective refractive indices. In some embodiments, the refractive index difference between the alternating layers is maximized in order to minimize the number of periods required to achieve a given reflectance, and the thickness and refractive index of each period determine the stop band and its wavelength limit.

[118] In some embodiments, the distributed Bragg reflector (DBR) layers 305 a-305z include a first DBR layer composed of a plurality of _{p-type In z} Al _x Ga _1-xz As layers and a second DBR layer overlaid on the first layer DBR and consisting of a plurality of layers In _w Al _y Ga _1-yw As p-type, where 0 <w <1, 0 <x <1, 0 <y <1, 0 <z <1, and y is greater than x.

[119] Figure 6 is a cross-sectional view of a portion of a solar cell assembly according to the present disclosure that is mounted on a panel or support substrate, wherein the figure shows two adjacent solar cells 601 and 701 and corresponding CICs 600 and 700, respectively.

[120] As noted above, the solar cell 601, 701 for space applications includes a cover glass 603, 703, respectively, over the semiconductor device to provide radiation resistant shielding of particles in outer space that can damage the semiconductor material. Cover glass 603, 703 is typically cerium dioxide doped borosilicate glass, which typically has a thickness of 76 to 152 μm and is adhered with transparent glue 602, 702, respectively, to the corresponding solar cell 601, 701.

[121] Contact pads of the first and second type of polarity are provided on each solar cell. In one embodiment, the backside metal 604 and 704, respectively, forms contacts of the first type of polarity. On the top surface of each solar cell, a metal contact 705 is provided along one edge of the solar cell to form a second polarity contact.

[122] A plurality of electrical interconnects 607 are provided, each of which consists of a silver-plated nickel-cobalt iron alloy strip, each interconnect welded to a respective pad 612 and 705 on each solar cell assembly to electrically connect adjacent assemblies solar cells array in the form of a serial electrical circuit.

[123] An aluminum honeycomb panel 606 having a carbon composite faceplate 605 with a coefficient of thermal expansion (CTE) that is substantially the same as germanium's fourth solar subcell in each solar cell is made with each CIC 600, 700 or solar assembly. elements installed on it.

[124] Another feature of the solar cell assembly in the embodiment shown in FIG. 6 is that each cover glass 603, 703 has a metal female clip 608, shown on the CIC 600, which makes contact with the surface of the cover glass 603 and continues down in a gap or gap along the side of the solar cell assembly 600 between the CIC 600 and 700 to provide electrical contact with a metal contact pad 612 on the rear surface of the CIC 600, which in turn provides electrical ground. Thus, the clamp 608 grounds the electrical charge accumulated on the surface of the cover glass 603 to ground the panel or spacecraft. Other configurations of grounding techniques for cover slip surface (s) 603, 703 are within the scope of this disclosure.

[125] Figure 7 is a graph illustrating the band gap of some bicomponent materials and their lattice constants. The bandgap and lattice constants of ternary materials are located on lines drawn between typical associated bicomponent materials (such as the ternary AlGaAs material, plotted between the dots of GaAs and AlAs, with a ternary material band gap between 1.42 eV for GaAs and 2.16 eV for AlAs, depending on the relative amount of the individual constituent elements). Thus, depending on the desired band gap, the materials included in the ternary materials can be appropriately selected for growth.

[126] FIG. 8 is an enlarged view of a portion of the graph of FIG. 7 illustrating various GaInAs and GaInP compounds with different gallium and indium fractions and specific compound locations on the graph.

[127] The present disclosure provides for a multi-junction solar cell that adheres to the design rule that as many subcells with high bandgap values should be included in order to achieve the goal of improving efficiency at high EOL temperatures. For example, subcells with high bandgap values allow a higher percentage of cell voltage to be maintained as the temperature rises, thereby reducing power loss as the temperature rises. As a result, both the performance of both the HT-BOL and the HT-EOL of the exemplary multi-junction solar cell according to the present disclosure can be expected to be greater than that of conventional cells.

[128] The exemplary solar cell described herein may require the use of aluminum in the semiconductor composition of each of the uppermost two subcells. The inclusion of aluminum is widely known in the semiconductor industry for compounds of Group III-V elements to reduce the performance of the BOL subcell due to deep level donor defects, higher doping compensation, shorter minority carrier lifetimes, lower cell voltage, and increased Eg / q - Voc metric. BOL. In short, the increase in Eg / q - Voc BOL may be the most problematic deficiency of subcells containing aluminum; other limitations can be mitigated by modifying the alloying schedule or reducing the base thickness.

[129] Taking into account the different requirements for satellites and spacecraft in terms of operational operating temperature, radiation exposure and service life, a number of sub-element designs can be achieved using the design principles of this disclosure, satisfying specific customer and flight program specific requirements, and several illustrative the embodiments are set out below along with calculating their end-of-life efficiency for comparison purposes. As described in more detail below, the performance of solar cells after irradiation with radiation was experimentally measured using an electron fluence of 1 MeV per square centimeter (abbreviated as e / cm ² in the text) so that comparisons can be made between current commercial devices and embodiments. solar cells discussed in this disclosure.

[130] As an example of various flight program requirements, a LEO satellite will typically experience radiation equivalent to an electron fluence of 5 × 10 ¹⁴ per square centimeter (hereinafter referred to as "5E14 e / cm ² " ) over a five-year service life. A satellite in geosynchronous low-earth orbit (GEO) will typically experience radiation in the range of 5 × 10 ¹⁴ e / cm ^{2 -} 1 × 10 ¹⁵ e / cm ² over a fifteen-year service life.

[131] For example, cell efficiency (%) measured at room temperature (RT) 28 ° C and high temperature (HT) 70 ° C at the beginning of life (BOL) and at the end of life (EOL), for a standard commercial solar element with three transitions (ZTJ) is presented in table 1:

Table 1

CONDITION Efficiency BOL 28 ° C 29.1% BOL 70 ° C 26.4% EOL 70 ° C 23.4% after irradiation with a fluence of 5E14 e / cm ² EOL 70 ° C 22.0% after irradiation with a fluence of 1E15 e / cm ²

[132] For a solar cell originally described in related US patent application Serial No. 14 / 828,206, filed August 17, 2015 (and corresponding published European patent application EP 3133650 A1), the corresponding data are presented in Table 2:

table 2

CONDITION Efficiency BOL 28 ° C 29.1% BOL 70 ° C 26.5% EOL 70 ° C 24.5% after irradiation with a fluence of 5E14 e / cm ² EOL 70 ° C 23.5% after irradiation with a fluence of 1E15 e / cm ²

[133] The solar cell described in earlier claims by the applicant has a slightly higher cell efficiency than the standard commercial solar cell (ZTJ) at BOL at 70 ° C. However, the solar cell described in one embodiment of the disclosure exhibits significantly improved cell efficiency (%) over a standard commercial solar cell (ZTJ) with 1 MeV electron transfer equivalent to a fluence of 5 × 10 ¹⁴ e / cm ² , and significantly improved Efficiency (%) of the cell compared to a standard commercial solar cell (ZTJ) with 1 MeV electron transfer equivalent to a fluence of 1 × 10 ¹⁵ e / cm ² .

[134] The simplest way to present the various embodiments of the present disclosure and their efficiencies as compared to the efficiency of the standard solar cell described above is to list the embodiments describing the composition of each subsequent subcell and their respective band gap and then the calculated efficiency ...

[135] Thus, for a four-junction solar cell that is made and described in the present disclosure, the four embodiments and their corresponding EOL data are represented as follows:

Embodiment 1 Band gap Composition Sub-element A 2.1 AlInGaP Sub-element B 1.73 InGaP / AlInGaAs or AlInGaAs / AlInGaAs Sub-element C 1.41 (B) GaAs Sub-element D 0.67 Ge

Efficiency at 70 ° C after irradiation with a fluence of 5E14 e / cm ² : 24.5%

Efficiency at 70 ° C after irradiation with a fluence of 1E15 e / cm ² : 23.5%

Embodiment 2 Band gap Composition Sub-element A 2.1 AlInGaP Sub-element B 1.67 InGaP / AlInGaAs or AlInGaAs / AlInGaAs Sub-element C 1.34 InGaAs Sub-element D 0.67 Ge

Efficiency at 70 ° C after irradiation with a fluence of 1E15 e / cm ² : 24.9%

Embodiment 3 Band gap Composition Sub-element A 2.1 AlInGaP Sub-element B 1.65 InGaP / AlInGaAs or AlInGaAs / AlInGaAs Sub-element C 1.30 (B) GaAs Sub-element D 0.67 Ge

Efficiency at 70 ° C after irradiation with a fluence of 1E15 e / cm ² : 25.3%

Embodiment 4 Band gap Composition Sub-element A 2.03 AlInGaP Sub-element B 1.55 InGaP / AlInGaAs or AlInGaAs / AlInGaAs Sub-element C 1,2 (B) GaAs Sub-element D 0.67 Ge

Efficiency at 70 ° C after irradiation with a fluence of 1E15 e / cm ² : 25.7%

[136] Although the differences in bandgap values among the various embodiments described above, i.e., on the order of 0.1-0.2 eV, may appear relatively small, such adjustments result in a surprising and unexpected increase in the efficiency of an EOL solar cell from 24, 4%, as reported in related US patent application Serial No. 14 / 828,206, filed August 17, 2015 (and in the corresponding published European patent application EP 3133650 A1) to 25.7% for the solar cell of embodiment 4 described above. Such a surprising and unexpected improvement, due to the relatively small change in band gap, implies a perceived understandable inventive step compared to the related configuration described in the related application and in the publication of the European patent application, since in the field of solar cell devices for space applications, even a small increase in efficiency is usually considered very important.

[137] Although the described embodiments of the present disclosure utilize a vertical stack of four sub-elements, various aspects and features of the present disclosure may apply to stacks with fewer or more sub-elements, i.e., two-jump members, three-jump members, five-jump members. , six, family, etc. transitions.

Claims (21)

1. A method of manufacturing a solar cell (200, 400, 450, 500) with four transitions, comprising: providing a substrate (300) for growing; forming a fourth solar sub-cell (D) located on top of or in the substrate (300) for growing; epitaxial growing of a variable intermediate layer (505) located on top of the fourth solar subcell (D) and substrate (300) for growing, followed by epitaxial growth of a sequence of semiconductor material layers containing multiple solar subcells, including a third solar subcell (C) located on top and lattice mismatched with respect to the substrate (300) for growth and having a band gap in the range of 0.9-1.6 eV, at least a second solar subcell (B) located on top of the third solar subcell (C) and having bandgap in the range of about 1.55-1.8 eV, and the upper first solar subcell (A) located on top of the second solar subcell (B) and having an aluminum content of more than 30% mole fraction and a band gap in the range of 2.0 -2.20 eV; in this case, the changing intermediate layer (505) changes in its composition to match the lattice parameter of the substrate (300) for growing on the one hand and the third solar subcell (C) on the other hand and consists of any of the semiconductor compounds of III-V group elements based on As, P, N, Sb taking into account the restrictions associated with the fact that the lattice parameter in the plane throughout its entire thickness should be greater than or equal to the lattice parameter in the plane of the substrate (300) for growth. 2. The method of claim 1, wherein the second solar subcell (B) has a band gap of approximately 1.73 eV and is lattice matched to the third solar subcell (C), and the upper first solar subcell (A) has a band gap 2.05 eV and matched in lattice parameter with the second solar subcell (B), and the average band gap of all four solar subcells is equal to or greater than 1.35 eV. 3. A method according to any one of the preceding claims, in which the upper first solar sub-element (A) consists of a base layer (In _x Ga _1-x ) _1-y Al _y P, where x is 0.505 and y is 0.142, which corresponds to the width of the forbidden zone 2.10 eV, and the emitter layer (In _x Ga _1-x ) _1-y Al _y P, where x is equal to 0.505 and y is 0.107, which corresponds to a band gap of 2.05 eV. 4. The method according to any of the preceding claims, further comprising the implementation of a tunnel diode (303, 304) located above the fourth solar subcell (D) and below the changing intermediate layer (505), the changing intermediate layer (505) being varied in composition to match by the lattice parameter of the third solar subcell (C) on the one hand and the tunnel diode (303, 304) on the other hand and consists of any of the semiconductor compounds of III-V group elements based on As, P, N, Sb, taking into account the limitations associated with by the fact that the lattice parameter in the plane must be greater than or equal to the lattice parameter in the plane of the third solar subcell (C) and differ from the lattice parameter in the plane of the tunnel diode (303, 304), and the energy of the forbidden zone must be greater than that of the fourth solar subcell (D). 5. A method according to any one of the preceding claims, in which the variable intermediate layer (505) is stepped in its composition from one to four jumps to match the lattice parameter of the third solar subcell (C) on one side and consists of InGaAs or (In _x Ga _1-x ) _y Al _1-y As, where 0 <x <1, 0 <y <1 and x and y are chosen so that the band gap also changes in the range of 1.15-1.41 eV throughout its thickness. 6. A method according to any of the preceding claims, wherein the variable intermediate layer (505) has a band gap in the range of 1.15-1.41 eV, or 1.2-1.35 eV, or 1.25-1.30 eV. 7. A method according to any one of the preceding claims, wherein either of 1) the emitter layer (320) or 2) the base layer (319) and the emitter layer (320) of the upper first solar subcell (A) has lattice constants that differ from the lattice constant the immediately adjacent second solar subcell (B). 8. A method according to any of the preceding paragraphs, further comprising: implementation of a distributed Bragg reflector (DBR) layer (305) adjacent to and located under the third solar sub-element (C) and positioned so that light can penetrate and pass through the third solar sub-element (C) and at least part of it can be reflected back into the third solar sub-element (C) from the DBR layer (305), and the distributed Bragg reflector layer (305) consists of a plurality of alternating layers of lattice-matched materials with an abrupt change in their respective refractive indices, while the refractive index difference between the alternating layers is maximized in order to minimize the number of periods required to achieve a given reflectance, both the thickness and refractive index of each period determine the stop band and its ultimate wavelength, and the DBR layer (305) includes a first DBR layer composed of multiple layers In _z Al _x Ga _1-xz As p-type, and second layer DBR located on top of the first DBR layer and consisting of a plurality of _{p-type In w} Al _y Ga _1-yw As layers, where 0 <w <1, 0 <x <1, 0 <y <1, 0 <z <1 and y more than x; and in this case, the changing intermediate layer (505) changes stepwise in its composition to match the lattice parameter of the DBR layer (305) on the one hand and the fourth solar subcell (D) on the other hand and consists of any of the semiconductor compounds of III-V group elements based on As, P, N, Sb taking into account the constraints associated with the fact that the lattice parameter in the plane must be greater than or equal to the lattice parameter in the plane of the DBR layer (305) and less than or equal to the lattice parameter in the plane of the fourth solar sub-element (D), and the energy of the band gap must be greater than that of the fourth solar subcell (D). 9. A method according to any of the preceding claims, further comprising: performing a first threading dislocation suppression layer having a thickness in the range of 0.10-1.0 microns, located over the growth substrate and having a composition that is different from the variable intermediate layer; and the second layer for suppressing the formation of threading dislocations having a thickness in the range of 0.10-1.0 microns and consisting of InGa (Al) P, and the second layer for suppressing the formation of threading dislocations is located on top and directly adjacent to the mentioned changing intermediate layer to reduce the propagation of threading dislocations , wherein said second layer of suppressing the formation of threading dislocations has a composition that differs from the composition of the first layer of suppressing the formation of threading dislocations and the changing intermediate layer, and wherein at least one of the upper sublayers of the changing intermediate layer (505) has a lattice constant greater than for adjacent layers (506, 306) with an upper sub-layer located on top of the changing intermediate layer (505). 10. Solar cell (200, 400, 450, 500) with four transitions, containing: growing substrate (300); a fourth solar sub-cell (D) located on top or in the substrate (300) for growing; a variable intermediate layer (505) located on top of the substrate (300) for growth, followed by a sequence of layers of semiconductor material containing many solar subcells, including a third solar subcell (C) located on top and lattice mismatched with respect to the substrate (300 ) for growing and having a bandgap in the range of 0.9-1.6 eV, at least a second solar subcell (B) located on top of the third solar subcell (C) and having a bandgap in the range of approximately 1.55-1 , 8 eV, and the upper first solar sub-cell (A), located on top of the second solar sub-cell (B) and having an aluminum content of more than 30% mole fraction and a band gap in the range of 2.0-2.20 eV; in this case, the changing intermediate layer (505) changes in its composition to match the lattice parameter of the substrate (300) for growing on the one hand and the third solar subcell (C) on the other hand and consists of any of the semiconductor compounds of III-V groups based on As, P, N, Sb taking into account the restrictions associated with the fact that the lattice parameter in the plane throughout its entire thickness should be greater than or equal to the lattice parameter in the plane of the substrate (300) for growth.

Images