HK1094915B - Multilayer solar cell - Google Patents

Description

Laminated solar cell

Technical Field

The present invention relates to a laminated solar cell, and more particularly, to a laminated solar cell in which a cell group module having a plurality of spherical solar cells inserted therein is incorporated as at least 1 type of solar cell module in 2 or more types of solar cell modules having different stacking sensitivity wavelength bands in order to effectively utilize a wide range of wavelength components in the solar spectrum.

Background

The spectrum of sunlight has a broad wavelength range from ultraviolet to far infrared with a peak value near 600nm on the ground, and in order to receive such sunlight and efficiently convert it into electric energy, a solar cell relying on a single energy band gap has a limited usable spectrum range, and there is a limit to the increase in efficiency of photoelectric conversion. Therefore, a solar cell has been proposed which is configured to divide the spectrum of sunlight into a plurality of sensitivity wavelength bands, create a plurality of types of solar cell modules (or unit solar cells or solar cell layers) capable of performing photoelectric conversion efficiently for each of the sensitivity wavelength bands, and perform photoelectric conversion by stacking them in order of the center wavelength length (large band gap) of the sensitivity wavelength band from the sunlight incidence side, thereby absorbing a wide range of sunlight spectrum.

Currently, the existing solar cell is proposed as follows.

(a) A solar cell is divided into a plurality of wavelength bands by optical filters, and a plurality of types of independent solar cell modules suitable for each sensitivity wavelength band are arranged on each light path. Such solar cells are described in the Potential for Photovoltaic Systems by Using multiple cells concept, n.s. alvi, c.e. bakus and g.w. madesen, conf.proc.12th IEEE Photovoltaic specialty Conference957 (1976).

(b) A plurality of semiconductor layers having different energy band gaps are grown in a crystalline state on a common substrate, and the semiconductor layers are integrated into a solar cell in which 2 solar cell layers are stacked.

(c) A solar cell in which a plurality of types of solar cell panels are individually produced using semiconductors having different sensitivity wavelength bands (band gaps) and arranged on the optical path of sunlight.

In "III-V Compounds For Solar Cell Applications (III-V group Compounds For Solar cells)" (A.W.Bett, F.Dimroth, G.Stollwerck and O.V.Sulima, appl.Phys.A69, 119-129(1999)), the above-mentioned (b) and (c) are described.

In any of the above (a) to (c), the unit solar cell of the tandem solar cell is formed by forming a pn junction in a planar semiconductor wafer or a semiconductor layer. The solar cell forming filter of the above (a) has a reduced performance due to optical loss and a high cost, and a space between a plurality of unit solar cells is large, and positioning and fixing thereof, etc. are laborious.

The solar cell of the above (b) is limited by the difference in crystal structure and lattice constant of the semiconductor species grown as crystals on one substrate, and it is difficult to form pn junctions of desired shapes having different band gaps. Furthermore, a tunnel junction is required to allow current to flow between the stacked solar cell layers; but the resistance of the tunnel junction portion is high. Further, since the photocurrents of the stacked solar cell layers are not uniform, there is a problem that the output current of the entire solar cell is limited by the lowest solar cell layer.

The solar cell of the above (c) is not limited in terms of crystal growth as in the solar cell of the above (b), but the unit solar cell on the sunlight incidence side needs a window through which light in a wavelength band that is not absorbed in the unit solar cell passes. When the number of stacked layers and the photosensitive area of the unit solar cell are increased, the area of the comb-shaped electrode part is increased, and the defect that the effective photosensitive area is easily reduced due to the position deviation of the unit solar cell exists. Further, similarly to the solar cell of (b), since the unit solar cells composed of a single pn junction are stacked, the output currents of the respective unit solar cells are not uniform, and there is a problem that the output of the entire solar cell is limited by the unit solar cell having a small output current.

The present invention has an object to provide a stacked solar cell which can eliminate the above-mentioned problems and can significantly improve the efficiency of photoelectric conversion of sunlight.

Disclosure of Invention

The laminated solar cell of the present invention is a laminated solar cell in which a plurality of solar cell modules having different sensitivity wavelength bands are incorporated and stacked, wherein the solar cell modules include a plurality of types of solar cell modules, and the solar cell modules are stacked such that modules having shorter central wavelengths of the sensitivity wavelength bands are located closer to the side on which solar light enters, and at least one type of solar cell module is configured by a cell module having a plurality of substantially spherical solar cells arranged in a plurality of rows and a plurality of columns. Since a plurality of types of solar cell modules having different sensitivity wavelength bands are included, power generation can be performed using sunlight in a wide wavelength range within the spectrum of sunlight. Since the transmittance is lower for light having a shorter wavelength, the solar cell modules having a shorter center wavelength in the sensitivity wavelength band are placed closer to the sunlight incidence side by the above-described lamination, and the photoelectric conversion efficiency of each solar cell module can be improved.

In a battery pack module incorporating a plurality of substantially spherical solar cells, the output current can be easily changed by changing the number of series connections and the number of parallel connections of a circuit for connecting the plurality of solar cells in series and parallel. Therefore, by changing the output current of at least 1 cell group module, it is easy to make the output currents of a plurality of types of solar cell modules uniform, which is advantageous in improving the photoelectric conversion efficiency of the solar cell.

Since the solar cells in the cell group module have substantially spherical pn junctions, the total area of the pn junctions of the cell group module can be increased by densely arranging the plurality of solar cells, thereby improving the photoelectric conversion efficiency. Further, each solar cell of the cell group module has a substantially spherical pn junction, and incident light to each solar cell encounters the pn junction 2 times, which is advantageous in improving photoelectric efficiency. The solar cells can be configured to have a light-blocking effect, which is advantageous in improving photoelectric conversion efficiency. The light reflected by the spherical surface changes the light path and enters other solar cells, so that the light absorption of the whole solar cell is improved.

The solar cells of each cell group module can be independently manufactured without being affected by the lattice constant of the semiconductor constituting the pn junction of the other solar cell modules.

Here, in addition to the above-described composition, the following composition may be suitably employed.

(1) At least one solar module is formed from a planar light-sensitive module having a planar common pn junction.

(2) There are 4 types of solar cell modules, 3 types of solar cell modules are configured from a cell group module having substantially spherical solar cells arranged in a plurality of rows and a plurality of columns, and 1 type of solar cell module is configured from a planar photosensitive module having a planar common pn junction.

(3) The solar cells arranged in a plurality of rows and a plurality of columns in the plurality of cell group assemblies are electrically connected by a plurality of leads extending in the row direction or the column direction and led out to the outside.

(4) Each battery group assembly has a series-parallel circuit for connecting the battery group assemblies in series-parallel via the plurality of leads.

(5) The solar cell module has a series circuit in which a plurality of types of solar cell modules are connected in series, and the series-parallel circuit of each of the plurality of types of solar cell modules is configured such that an output current of each of the plurality of types of solar cell modules is substantially equal to an output current of the planar photosensitive module.

(6) Each of the cell group modules has 2 layers of a plurality of spherical solar cells arranged in a plurality of rows and a plurality of columns on a plane, and the 2 layers of solar cells are arranged so as to be close to each other in a plan view without overlapping.

(7) The planar photosensitive element is disposed in the lowermost layer so as to be located below the plurality of cell group elements, and a reflecting member capable of reflecting sunlight is provided on the lower portion or lower surface side of the planar photosensitive element.

(8) In any solar cell module other than the solar cell module closest to the incident side in the incident direction of sunlight, a mirror film that reflects light in a sensitivity wavelength band that is easily absorbed by the solar cell module on the upper side thereof is formed on the surface of the solar cell module.

(9) In the cell group module, a plurality of solar cells are embedded in transparent glass or a synthetic resin material.

(10) Each transparent member made of transparent glass or synthetic resin is bonded to the upper surface of the solar cell module closest to the incident side in the sunlight incident direction.

(11) The planar photosensitive element is disposed in the lowermost layer below the plurality of cell group members, and the 3 kinds of cell group members include 1 st to 3 rd cell group members stacked in this order from the sunlight incident side, the 1 st cell group member includes a plurality of solar cells in which a substantially spherical pn junction is formed at a substantially spherical GaP single crystal surface layer portion, the 2 nd cell group member includes a plurality of solar cells in which a substantially spherical pn junction is formed at a substantially spherical GaAs single crystal surface layer portion, and the 3 rd cell group member includes a plurality of solar cells in which a substantially spherical pn junction is formed at a substantially spherical Si single crystal surface layer portion.

(12) The planar photosensitive assembly of item (11) has a planar common pn junction formed in an InGaAs semiconductor layer formed on an n-type InP semiconductor substrate.

(13) The planar photosensitive element is disposed on the uppermost layer on the upper side of the plurality of cell group members, and the 3 kinds of cell group members include 1 st to 3 rd cell group members stacked in this order from the sunlight incident side, the 1 st cell group member includes a plurality of solar cells in which a substantially spherical pn junction is formed at a substantially spherical GaAs single crystal surface layer portion, the 2 nd cell group member includes a plurality of solar cells in which a substantially spherical pn junction is formed at a substantially spherical Si single crystal surface layer portion, and the 3 rd cell group member includes a plurality of solar cells in which a substantially spherical pn junction is formed at a substantially spherical Ge single crystal surface layer portion.

(14) The planar photosensitive element of item (13) has a planar common pn junction formed in a GaAsP semiconductor layer formed on an n-type GaP semiconductor substrate.

(15) There are 2 kinds of flat photosensitive members, and 1 or more battery group members are interposed between the 2 kinds of flat photosensitive members.

(16) Various solar cell modules are formed in a cylindrical shape, and the solar cell modules are stacked in a concentric circle shape.

Drawings

Fig. 1(a) to (g) are cross-sectional views of Si single crystal and the like in a plurality of steps of manufacturing a spherical Si solar cell.

Fig. 2 is a cross-sectional view of a spherical Ge solar cell.

Fig. 3 is a cross-sectional view of a GaP single crystal or the like in a plurality of steps of manufacturing a GaP solar cell.

Fig. 4 is a sectional view of a GaAs single crystal or the like in a plurality of steps of manufacturing a GaAlAs/GaAs solar cell.

Fig. 5 is a plan view of the Si battery group assembly.

Fig. 6 is a sectional view taken along line VI-VI of fig. 5.

Fig. 7 is a sectional view taken along line VII-VII of fig. 5.

FIG. 8 is a top view of the InGaAs/InP planar photosensitive assembly.

Fig. 9 is a sectional view taken along line IX-IX of fig. 8.

Fig. 10 is a top view of a GaAsP/GaP planar photosensitive element.

Fig. 11 is a cross-sectional view taken along line XI-XI of fig. 10.

Fig. 12 is a plan view of the tandem solar cell of example 1.

Fig. 13 is a cross-sectional view of the tandem solar cell of fig. 12.

Fig. 14 is a distribution diagram of the relative energy density of sunlight and the relative spectral sensitivity of a solar cell incorporated in the solar cell of example 1.

Fig. 15 is an explanatory view for explaining incidence, reflection, absorption, and the like of the solar cell of example 1.

Fig. 16 is a schematic circuit diagram of a series-parallel circuit and a series circuit of the solar cell of example 1.

Fig. 17 is a cross-sectional view of a 2 nd example solar cell.

Fig. 18 is a cross-sectional view of a 2 nd example solar cell.

Fig. 19 is a distribution diagram of the relative energy density of sunlight and the relative spectral sensitivity of a solar cell incorporated in the solar cell of example 2.

Fig. 20 is a perspective view of a tandem solar cell according to another embodiment.

Fig. 21 is a cross-sectional view of the solar cell of fig. 20.

Detailed Description

First, 4 kinds of substantially spherical solar cells that function as unit cells constituting the laminated solar cell of the present invention are described; next, a battery pack module incorporating a spherical solar cell will be described; next, a solar cell in which a plurality of cell group modules and 1 flat photosensitive module are incorporated will be described. Next, a cylindrical solar cell in which a plurality of cylindrical cell group members are stacked in a concentric shape will be described.

The solar cell is the same as that proposed by the inventor of the present application in japanese patent No. 3262174. In the production of this solar cell (spherical photosensitive cell), a spherical semiconductor crystal is produced, a substantially spherical pn junction is formed in the surface layer portion of the semiconductor crystal, positive and negative electrodes are provided at surface positions facing each other across the center of the semiconductor crystal, and the positive and negative electrodes are connected to both poles of the pn junction.

Such a solar cell hardly has directivity in the incident direction of sunlight, and therefore exhibits good light-receiving ability even if the incident angle of direct solar light changes, and also exhibits good light-receiving ability for reflected light in the surroundings. The solar cell is characterized in that incident light is easily blocked in the solar cell and photoelectric conversion is efficiently performed by utilizing a spherical pn junction.

In the manufacture of such a spherical solar cell, it is preferable to use a spherical semiconductor crystal having a size close to that of the solar cell to reduce the loss of the semiconductor material. As a method for producing the spherical semiconductor crystal, for example, a method proposed by the present inventors in japanese patent No. 3231244 can be used. That is, the semiconductor droplets in a molten state are allowed to fall freely from the upper part of the drop tube, and the droplets in the course of falling are supercooled and solidified by applying a stimulus from the outside, thereby producing spherical or granular single crystals.

When a compound semiconductor containing an element having a high vapor pressure is used, for example, a method proposed by the present inventors in japanese patent No. 3287579 can be used. In this method, a compound semiconductor raw material and an element having a high vapor pressure among the elements constituting the raw material are contained in a sealed ampoule together with a shielding gas, and are allowed to fall freely from the upper part of a fall tube, and the semiconductor raw material in a molten state is also solidified in free fall in the same manner as described above, thereby producing a spherical or granular single crystal. However, instead of these methods, a cube having a volume close to that of the solar cell may be cut out of a large single crystal, and the cube may be processed into a spherical shape by a mechanochemical method to produce a spherical single crystal. Spherical or substantially spherical solar cells are produced from these spherical single crystals, and a solar cell module (cell group module) having a wavelength band of sensitivity specific to sunlight is produced from a plurality of solar cells. The spectral solar cell (tandem solar cell) of the present application is a cell in which 2 or more solar cell modules having different sensitivity wavelength bands are combined and synthesized, and a planar pn junction module (planar module) is sometimes combined and synthesized as needed.

First, the structure and the manufacturing method of the plurality of types of solar cells (unit solar cells) incorporated in the tandem solar cell of the present invention will be described. The solar cells described herein may be fabricated using the above-described known techniques or other known techniques and are therefore described briefly. Fig. 1(a) to (g) show production steps in producing a substantially spherical Si solar cell 10 composed mainly of a substantially spherical silicon (Si) single crystal 11, which is incorporated in a solar cell module having a sensitivity wavelength band in an intermediate wavelength region (about 500nm to 1100nm) in the solar spectrum. Si is an indirect-transition semiconductor having an energy band gap of 1.12 eV.

When the granular p-type silicon single crystal 11 shown in FIG. 1(a) was produced, a certain amount of Si droplets were allowed to fall freely from the upper part of a falling tube through which an inert gas flowed, and during the fall, the granular Si droplets were formed into a spherical shape by surface tension, and a physical stimulus such as a slight point of contact with the droplets was applied from a supercooled state during the fall to rapidly solidify the granular P-type silicon single crystal 11, thereby obtaining a p-type silicon single crystal 11 having a diameter of about 1.2 mm.

The convex portion of the p-type silicon single crystal 11 is formed at the final stage of solidification. As shown in fig. 1(b), the reference surface 12 is formed by cutting the convex portion into a flat surface. The reference surface 12 is a flat surface having a diameter of about 0.3 mm. The reference surface 12 is used for positioning in the following processes such as impurity diffusion, electrode formation, output characteristic measurement, and wiring. Next, as shown in fig. 1(c), a silicon oxide film 13 is formed over the entire surface. Next, as shown in fig. 1(d), the silicon oxide film 13 is left on the reference surface 12 and the vicinity of the outer periphery thereof, and the other silicon oxide film 13 is removed. Next, As shown in fig. 1(e), the silicon single crystal 11 of fig. 1(a) is heated to diffuse phosphorus (P) or arsenic (As) As an n-type impurity, thereby forming an n-type diffusion layer 14, and a substantially spherical pn junction 15 is formed between the P-type Si single crystal 11 and the n-type diffusion layer 14. When the n-type impurity is diffused, the thin Si oxide film 16 is also formed. The surface of the p-type Si single crystal 11 is left at and near the reference plane 12 so as not to be covered with the diffusion layer 14. Next, as shown in fig. 1(f), etching is performed to remove the silicon oxide films 13 and 16 once, and then the antireflection film 17 made of a thin silicon oxide film is formed on the entire surface. Next, as shown in fig. 1(g), when a paste containing silver is applied in a dot form from the reference surface 12 toward the center portion of the surface of the p-type silicon single crystal 11 and the center portion of the surface of the n-type diffusion layer 14 with the reference surface 12 as a positioning mark and baked, a positive electrode 18 and a negative electrode 19 are obtained in which the silver-penetrated thin silicon oxide film 17 (antireflection film) is in ohmic contact with the surfaces of the p-type silicon single crystal 11 and the n-type diffusion layer 14, respectively. Since these electrodes 18 and 19 are located at positions facing each other across the center of the single crystal silicon 11, the symmetry between the light input and the photoelectromotive force distribution is maintained, the deviation of the current distribution is small, and the pn junction 15 functions efficiently.

Fig. 2 is a cross-sectional view of a germanium solar cell 20 which is incorporated in a solar cell module having a sensitivity wavelength band of a long wavelength region (about 800nm to 1600nm) in the solar spectrum and is manufactured mainly from a substantially spherical germanium (Ge) single crystal. Germanium is an indirect-transfer type semiconductor having an energy band gap of 0.66eV, and the germanium solar cell 20 can be manufactured through the same process as the above-described silicon solar cell 10.

Fig. 2 shows a p-type germanium single crystal 21 having a diameter of about 1.2mm, a reference plane 22, an n-type diffusion layer 24 formed by thermally diffusing an n-type impurity (phosphorus or arsenic), a pn junction 25, an antireflection film 26, a positive electrode 27 formed of tin containing a small amount of indium and in ohmic contact with the p-type germanium single crystal 21, and a negative electrode 28 formed of tin containing a small amount of antimony and in ohmic contact with the n-type diffusion layer 24.

Fig. 3(a) to (g) show the manufacturing steps for manufacturing a substantially spherical gallium phosphide solar cell 30 incorporated in a solar cell module having a sensitivity wavelength band in a short wavelength region (about 300nm to 600nm) in the solar spectrum and produced mainly from a spherical gallium phosphide (GaP) single crystal. Gallium phosphide (GaP) is an indirect transition type semiconductor having an energy band GaP of about 2.25 eV. the gallium phosphide solar cell 30 has a sensitivity wavelength band on the short wavelength side in the solar spectrum. In order to produce this solar cell 30, first, a cube having a side length of about 1.6mm was cut out from an n-type gallium phosphide single-crystal ingot, and the cube was processed by mechanochemical polishing to produce a spherical n-type gallium phosphide single crystal 31 having a diameter of about 1.2mm as shown in fig. 3 (a). Next, as shown in FIG. 3(b), the lower end of the spherical n-type gallium phosphide single crystal 31 was cut to form a reference plane 32. Next, as shown in FIG. 3(c), a silicon nitride film 33 (Si) is formed on the entire surface of the gallium phosphide single crystal 31₃N₄). Next, as shown in FIG. 3(d), the reference surface 32 and the vicinity of the outer periphery thereof are leftThe silicon nitride film 33 of (2) is used as a diffusion mask, and the other silicon nitride film 33 is removed.

Next, as shown in fig. 3(e), a diffusion layer 34 made of p-type gallium phosphide diffused with a p-type impurity such as zinc (Zn) and a substantially spherical pn junction 35 as a boundary between the diffusion layer 34 and the n-type gallium phosphide single crystal 31 are formed. After the diffusion layer 34 and the pn junction 35 are formed, the silicon nitride film 33 serving as a diffusion mask is completely removed. Next, as shown in fig. 3(f), an antireflection film 36 composed of a thin silicon oxide film is formed on the entire surface. Next, as shown in fig. 3(g), with the reference plane 32 as a positioning target, pastes mainly composed of gold and containing zinc and germanium as dopants respectively are applied in a dot shape to the center of the surface of the p-type diffusion layer 34 and the center of the surface of the n-type gallium phosphide single crystal 31 from the reference plane 32, and a short-time heating treatment is performed at a high temperature, whereby a positive electrode 37 and a negative electrode 38 are formed, which penetrate through the thin silicon oxide film and are in ohmic contact with the p-type gallium phosphide layer 34 and the n-type gallium phosphide single crystal 31, respectively.

Fig. 4(a) to (d) show a manufacturing process for manufacturing a substantially spherical GaAlAs/GaAs solar cell 40 composed of a substantially spherical gallium arsenide (GaAs) single crystal as a main component, which is incorporated in a solar cell module having a sensitivity wavelength band in a short wavelength region (about 500nm to 850nm) in a solar spectrum. Gallium arsenide (GaAs) is a direct-transition semiconductor having an energy band gap of 1.43eV, and has an energy band gap between silicon and gallium phosphide as described above.

First, as shown in FIG. 4(a), a substantially spherical n-type gallium arsenide single crystal 41 having a diameter of about 1.2mm is produced. The gallium arsenide single crystal 41 may be formed by a mechanochemical process, as described above for the gallium phosphide single crystal 31. However, in order to reduce the loss of raw materials and obtain a good single crystal, the present inventors have made the method proposed in japanese patent No. 3287579. In this method, an n-type gallium arsenide material and a small amount of arsenic are vacuum-sealed in a quartz ampoule, and the gallium arsenide material inside is heated from the outside to be in a molten state, and then cooled and solidified while being allowed to fall freely. In a state of a slight gravity during free fall, the gallium arsenide melt is formed into a spherical shape by surface tension, and a physical stimulus (excitation) is applied in a supercooled state to rapidly solidify the melt, thereby producing a substantially spherical gallium arsenide single crystal 41 shown in fig. 4 (a). Next, as shown in fig. 4(b), a ga0.2 al0.8as layer 49 (3-membered mixed crystal semiconductor) was grown as a thin film on the surface of the n-type gallium arsenide single crystal 41 by liquid phase epitaxy. At this time, gallium arsenide single crystal 41 is immersed at a high temperature in a vessel in which a small amount of gallium melt of gallium arsenide As a raw material and zinc As a dopant is added to the gallium melt and is kept for a short time, and then cooled, whereby a Ga0.2 Al0.8As layer 49 is epitaxially grown on the surface. When a Ga0.2 Al0.8As crystal is grown, zinc diffuses toward the n-type gallium arsenide single crystal 41 to form a p-type gallium arsenide layer 44, and a pn junction 45 is formed on the surface of the gallium arsenide layer 44.

Next, as shown in fig. 4(c), after forming an antireflection film 46 made of a silicon oxide film on the surface, the convex portion on the surface of the n-type gallium arsenide single crystal is horizontally cut to form a reference surface 42 having a diameter of about 0.3 mm. Next, as shown in fig. 4(d), with reference surface 42 as a positioning mark, pastes mainly composed of crystal grains and containing zinc and germanium as dopants respectively are applied in a dot shape to the center of the surface facing p-type GaAlAs layer 49 and the center of the surface facing n-type gallium arsenide single crystal 41 from the reference surface 44 side, and heat treatment is performed at a high temperature for a short time. By this heat treatment, a metal thin film of gold or the like is formed to penetrate through the silicon oxide film 46 (antireflection film) and to be in ohmic contact with the p-type GaAlAs layer 49 and the positive electrode 47 and the negative electrode 48 of the n-type gallium arsenide single crystal, respectively.

In addition, when the GaAlAs/GaAs solar cell 40 is manufactured, the sensitivity wavelength band can be shifted to the short wavelength side by forming the pn junction 45 in the GaAlAs layer 49 or changing the composition ratio of the GaAlAs layer 49 to change the energy band gap. Instead of providing the GaAlAs layer 49, impurities may be diffused into the spherical n-type gallium arsenide single crystal 41 to form a homojunction type pn junction.

Fig. 5 to 7 show a silicon cell group module 70 (silicon solar cell module) in which a plurality of silicon solar cells 10 are arranged in a plurality of rows and a plurality of columns. Fig. 5 to 7 conceptually show an example of a module in which 100 cells are incorporated, but an actual silicon cell group module incorporates hundreds or thousands of silicon solar cells.

The structure and manufacturing method of the silicon cell group assembly 70 will be described with reference to fig. 5 to 7. First, a silicon solar cell array 71 in which 10 solar cells 10 are connected in parallel at equal intervals between a pair of leads (leads plated with silver on copper wires having a diameter of about 0.1mm) is manufactured.

A positive lead 73 and a negative lead 74 were bonded to the positive electrode 18 of the solar cell 10 and the negative electrode 19 of the solar cell, respectively, to produce 10 solar cell arrays 71. The 5 arrays 71 are arranged in parallel at equal intervals in the upper layer, the 5 arrays 71 are arranged in parallel at equal intervals in the lower layer, the array 71 arranged in the lower layer is positioned between the arrays 71 in the upper layer, and the upper and lower solar cells 10 are close to each other in a plan view without overlapping. Then, it is molded integrally with a synthetic resin 75a (e.g., a silicone resin having flexibility). The upper and lower solar cells 10 are also approached without overlapping side view. Solar cells 10 in 5 rows and 10 columns are arranged in a planar manner on the upper layer, and solar cells 10 in 5 rows and 10 columns are also arranged in a planar manner on the lower layer. An actual silicon cell group assembly 70 in which a plurality of solar cells are arranged in a matrix of rows and columns is a thin, flexible plate-like structure. But may also constitute a non-flexible component.

A transparent glass sheet 76 (having a thickness of about 0.2 mm) is bonded to the lower surface of the synthetic resin 75 a. The transparent glass sheet 76 maintains the mechanical strength of the silicon solar cell module 70 and also serves as a reference plane for bonding with other solar cell modules. The 2 ends of the positive lead 73 and the negative lead 74 after resin molding are extended to the outside of the transparent synthetic resin 75a so as to be electrically connected to other solar cell arrays and other solar cell modules. A series-parallel circuit 75 (refer to fig. 16) connecting 100 silicon solar cells 10 in series-parallel is formed with 10 positive lead wires 73 and 10 negative lead wires 74, and the series-parallel circuit 75 is explained later on with reference to fig. 16.

A cell group module 80 (solar cell module) can also be produced by incorporating a germanium solar cell 20 in place of the silicon solar cell 10 in the same manner as the production of the silicon cell group module 70 described above (see fig. 17). By incorporating the gallium phosphide solar cell 30, a cell group module 90 (solar cell module) can be produced in place of the silicon solar cell 10 (see fig. 13). By incorporating GaAlAs/GaAs solar cells 40, a cell group module 100 (solar cell module) can be manufactured instead of the silicon solar cells 10 (see fig. 13 and 17). The series-parallel circuit of these assemblies 80, 90, 100 is also described below, as is the series-parallel circuit 75 of the silicon cell cluster assembly 70.

The present inventors have disclosed a solar cell module incorporating such a plurality of spherical solar cells in international publication No. WO2004/001858 and the like.

Next, fig. 8 and 9 show an InGaAs/InP planar photosensitive element 60 of a solar cell module (unit module) incorporated in the tandem solar cell of the present invention as an example, having a sensitivity wavelength band to a spectrum of a long wavelength region (about 900nm to 1700nm) of sunlight.

On the surface of an n-type InP substrate 61, an n-type In 0.53 Ga 0.47 As layer 62 is epitaxially grown, and zinc As a p-type impurity is diffused from the n-type layer to form a p-type In 0.53 Ga 0.47 As layer 64, thereby forming a planar common pn junction 65. Si may be diffused in the reaction₃N₄Used As a diffusion mask, is selectively diffused to leave the periphery of the n-type In 0.53 Ga 0.47 As layer 62, thereby forming a p-type layer 64.

Although not shown, an n-type indium phosphide (InP) having a larger band gap than that of the InGaAs layer 64 may be epitaxially grown and then a p-type impurity may be diffused from the surface thereof to form a pn junction in the InGaAs layer 64. By providing the indium phosphide layer as a window layer, the recombination rate of the surface is reduced, and the photoelectric conversion efficiency can be improved. The composition ratio of In and Ga described above is merely an example and may be changed.

Next, as shown in fig. 8, a cold mirror film 66 is formed on the surface of the p-type InGaAs which is the light-receiving surface. The cold mirror film 66 is formed of a dielectric multilayer film that reflects light having a wavelength of about 1100nm or less and transmits light having a wavelength longer than the wavelength. The dielectric multilayer films being alternately stackedHigh refractive index dielectric (TiO)₂、Ta₂O₅Etc.) and a low refractive index dielectric (SiO)₂) The thickness and the number of films are set in consideration of the wavelength and reflectance of the reflection.

A negative electrode 68 (gold containing a small amount of germanium, nickel) is provided so as to be in ohmic contact with the entire lower surface of the n-type InP substrate 61; a positive electrode 67 (gold containing a small amount of zinc) formed in a strip shape to increase a photosensitive area is disposed so as to be in ohmic contact with the surface of the p-type InGaAs layer 64. The planar photosensitive element 60 may be fabricated according to well-known InGaAs/InP long wavelength photodiode fabrication techniques. Next, a positive lead 67a and a negative lead 68a composed of silver-plated leads (diameter 0.1mm) on copper wires were welded to the positive electrode 67 and the negative electrode 68, respectively.

Fig. 10 and 11 are a plan view and a cross-sectional view of a GaAsP/GaP planar photosensitive element 50 incorporated in the tandem solar cell of the present invention, which is an example of a solar cell element (unit element) having a sensitivity wavelength band to a short wavelength region (about 300nm to 600nm) in a solar spectrum.

On the n-type gallium phosphide substrate 51, a GaAs 0.1P 0.9 layer 52 was formed by a well-known vapor phase epitaxial growth method. In the case of this composition, GaAsP is an indirect-type mobile semiconductor having an energy band gap of about 2.21 eV. Next, zinc as a P-type impurity is diffused from the GaAsP layer 52 to form a P-type GaAs 0.1P 0.9 layer 54, thereby forming a pn junction 55 in the GaAs P layer 54. Although not shown, a diffusion mask Si is provided at the periphery of the surface of the n-type GaAs P layer 52₃N₄The film is subjected to zinc diffusion to form a planar pn junction. This method is also used in the known manufacturing method of yellow Light Emitting Diodes (LEDs).

A positive electrode 57 (gold containing a small amount of zinc) and a negative electrode 58 (gold containing a small amount of germanium, nickel) which are in ohmic contact with the surfaces of the GaAs P layer 54 and the gallium phosphide substrate 51, respectively, are provided. In order to increase the light-sensing area of the planar light-sensing member 50, the positive electrode 57 and the negative electrode 58 are formed in a thin band shape as shown in the drawing, and are aligned at positions on both sides. A transparent antireflection film 56 is provided on the surface of the light-sensing window surrounded by the strip electrode 57. The P-type GaAs P layer 54 serves as a light-sensing surface of the GaAsP/GaP planar light-sensing module 50, and in the case of a solar cell 300 (see fig. 17) described later, light having a long wavelength that has passed through the GaAsP/GaP planar light-sensing module 50 enters the 3-layer solar cell module side disposed below the module 50. Next, a positive lead 57a and a negative lead 58a were welded to the 2 ends of the positive electrode 57 and the negative electrode 58, respectively, with lead wires (diameter 0.1mm) plated with silver on copper wires, so as to be electrically connected, and the lead wires 57a, 58a were led out to the outside of the planar photosensitive assembly 50.

Next, the tandem solar cell 200 of example 1 will be described.

Fig. 12 and 13 are a plan view and a cross-sectional view of a tandem solar cell 200 configured by 4 solar cell modules of 4 types, i.e., a gallium phosphide cell group module 90, a GaAlAs/GaAs cell group module 100, a silicon cell group module 70, and an InGaAs/InP plane photosensitive module 60.

In the tandem solar cell 200, the solar cell modules 90, 100, 70, and 60 having different sensitivity wavelength bands in the solar spectrum are stacked such that the shorter the center wavelength of the sensitivity wavelength band, the closer to the side on which solar light enters. As is clear from fig. 14, the relationship between the center wavelengths of the sensitivity wavelength bands of the solar cell modules 90, 100, 70, and 60 is: the center wavelength of the assembly 90 (about 450nm) < the center wavelength of the assembly 100 (about 700nm) < the center wavelength of the assembly 70 (about 800nm) < the center wavelength of the assembly 60 (about 1300 nm). Therefore, the aluminum nitride substrate 201 is disposed at the lowermost layer, the InGaAs/InP planar photosensitive module 60, the silicon cell group module 70, the GaAlAs/GaAs cell group module 100, and the gallium phosphide cell group module 90, which are woven into the transparent synthetic resin 202, are stacked in this order on the substrate and bonded by transparent adhesive, and the transparent glass protective layer 203 is stacked on the uppermost layer where the photosensitive surface that receives sunlight is formed and bonded by transparent adhesive.

Positive and negative leads 67a and 68a of the module 60, positive and negative leads 73 and 74 of the module 70, positive and negative leads 103 and 104 of the module 100, and positive and negative leads 93 and 94 of the module 90 extend to the outside of each module, respectively, constituting series-parallel circuits 75, 105, 95 (refer to fig. 16) of each module 70, 100, 90.

Fig. 14 conceptually shows a solar spectrum obtained by the solar spectrum analyzer, spectral sensitivity characteristics (solid line) of the tandem solar cell 200, and spectral sensitivity characteristics when the solar cells 30, 40, 10 and the like constituting the cell are used alone.

In fig. 14, the band gap portion (shaded portion in the figure) of the spectral sensitivity characteristic of the solar spectrum and the tandem solar cell 200 is an unused portion of light energy that cannot be photoelectrically converted in the solar cell 200, and the long wavelength spectrum portion exceeding the sensitivity wavelength region of the spectral sensitivity characteristic of the solar cell 200 is an unused portion of energy that has passed through the solar cell 200. They are all loss energy that cannot be photoelectrically converted, and thus it is desirable to minimize them.

The components 90, 100, 70, 60 are used individually, not only is the sensitivity wavelength band narrow, but also the energy portion of the energy band that is excessively larger than the received light cannot be effectively used as an output. Fig. 14 shows that by stacking and combining solar cell modules having different energy band gaps (corresponding to sensitivity wavelength bands), the usable wavelength region (blank portion in the figure) is widened, and high photoelectric conversion efficiency is achieved.

Fig. 15 is an explanatory view for explaining the following 3 cases of the optical path of incident light and the optical path, reflection and absorption state of reflected light in the tandem solar cell 200. As is clear from the figure, the laminated solar cell 200 in which the spherical or substantially spherical solar cells 30, 40, and 10 are incorporated is effective.

Case 1: sunlight perpendicularly incident on the transparent cover glass 203 travels perpendicularly in each of the solar cells 30, 40, 10 and the module 60 on the optical path.

The sunlight that travels vertically after removing the light reflected at the interface having the different refractive index and the light absorbed by the substance other than the solar cell is absorbed by the solar cell characteristics that basically reflect the band gap, and contributes to photoelectric conversion. In such a tandem solar cell 200, since the solar cells 30, 40, and 10 are arranged in order of the higher energy band gap from the sunlight incident side, light having a short wavelength to light having a long wavelength is absorbed in order by the solar cells 30, 40, and 10 and the module 60. The light that has not been absorbed by the upper cell on the incident side enters the lower solar cell, the light that has not been absorbed enters the lower solar cell, and the light that has not been absorbed by the last module 60 becomes transmission loss.

In this way, the upper solar cell acts as a filter to the lower solar cell and the assembly 60, thereby reducing the rate at which excess light energy is received and converted to heat energy. The cold mirror 66 formed on the upper surface of the InGaAs/InP planar photosensitive member 60 having the longest sensitivity wavelength band functions as a filter that reflects light in a wavelength region shorter than the longest wavelength at which the silicon solar cell 10 can perform photoelectric conversion and transmits light in a wavelength region longer than the wavelength. Thus, the InGaAs/InP planar photosensitive assembly 60 is prevented from absorbing excessive light energy, temperature rise of the planar photosensitive assembly 60 is suppressed, and durability thereof is improved. Similarly, the upper solar cell absorbs light having excessive energy to perform photoelectric conversion with respect to the lower solar cell, and thus the temperature rise of the solar cells 100 and 70 is also suppressed.

In a substantially spherical solar cell, when light passes through the solar cell, light absorption occurs from the incident point in the traveling direction according to the amount of light energy, but since the same pn junction is present on the opposite side with respect to the center of the solar cell, light having a long wavelength within the sensitivity wavelength band is absorbed, and the sensitivity wavelength band is broadened.

Case 2: the incident light is reflected by the surface of the solar cell.

As shown in fig. 15, light reflected by the surface of the spherical solar cells 30, 40, and 10 enters other solar cells, and is absorbed and transmitted according to the optical characteristics thereof. Light reflection occurs not only in the solar cell but also in the positive and negative leads of the solar cell and the transparent glass sheets 96, 106, 76. The reflected light is repeatedly reflected inside the modules 90, 100, 70, 60, causing the light to spread throughout the module. Therefore, light is also incident on the lower side (the side opposite to the light-receiving side) of the solar cell to which direct light does not reach, and an effect of increasing the output of the entire solar cell is obtained. This effect can further improve the light passing between the upper solar cells by the method of disposing the lower solar cells, the transparent glass, and the filler such as TiO 2.

Case 3: sunlight obliquely incident on the surface is captured and blocked inside the solar cell. Since the refractive index of the solar cells 30, 40, and 10 is large, a light blocking effect by total reflection occurs in the solar cells depending on the angle of incident sunlight, and a high output effect is expected by generating a component for photoelectric conversion of the pn junction in the solar cells.

Case 4: light is blocked between the transparent cover glass 203 and the cold mirror 66 of the module 60, and the light absorption and photoelectric conversion efficiency are improved.

Fig. 16 shows an example of a series circuit 205 for connecting the modules 90, 100, 70, and 60 in series in the tandem solar cell 200 in which the modules 90, 100, 70, and 60 having the same light-receiving section surface area are stacked, and an optimum series-parallel circuit 95, 105, and 75 for connecting the plurality of solar cells 30, 40, and 10 in each of the modules 90, 100, and 70 in series-parallel to maximize the output of the tandem solar cell 200. The series-parallel circuits 95, 105, 75 basically constitute the output currents of the blocks 90, 100, 70 equal to the output current of the block 60 having the smallest output current, respectively, and the series-parallel circuits 95, 105, 75 basically constitute the positive and negative leads 93, 95, 103, 104, 73, 74, 67a, 68a effectively utilized as described above.

When the maximum output current of the InGaAs/InP planar photosensitive module 60 is I, it is assumed that the maximum output current when all the solar cells 30 of the gallium phosphide cell group module 90 are connected in parallel is 2I, the maximum output current when all the solar cells 40 of the GaAlAs/GaAs cell group module 100 are connected in parallel is 3I, and the maximum output current when all the solar cells 10 of the silicon cell group module 70 are connected in parallel is 4I. The above case will be described as an example.

As shown in fig. 16, in the module 90, when the number of series circuits of the series-parallel circuit 95 is set to 2, the output current is I. In the module 100, if the number of series circuits of the series-parallel circuit 105 is set to 2, the output current is I. In the block 70, if the number of series circuits of the series-parallel circuit 75 is set to 4, the output current is I. The output currents of the elements 90, 100, 70 are each I, equal to the output current I of the element 60. When the output currents of the constituent modules 90, 100, 70, 60 are the same, the modules 90, 100, 70 exhibit the maximum power generation capacity.

The description will be further specifically made. That is, the maximum output currents of 1 solar cell 30, 40, 10 are I30, I40, I10, respectively, the number of parallel solar cells 30, 40, 10 is N30, N40, N10, respectively, and the output current of the module 60 is I.

The parallel numbers are set so that the formula I30 × N30 ═ I40 × N40 ═ I10 × N10 ═ I, and the output currents of the elements 90, 100, 70, and 60 have substantially the same value.

Assuming that the maximum output voltages of 1 solar cell 30, 40, 10 are V30, V40, V10, the numbers of the plurality of solar cells 30, 40, 10 connected in series are M30, M40, M10, and the output voltage of the module 60 is V60, the output voltage V of the tandem solar cell 200 is (V30 × M30) + (V40 × M40) + (i10 × M10) + V60.

In this way, by adjusting the number of parallel connections and the number of series connections for connecting the solar cells in series and parallel among the plurality of modules 90, 100, 70, and 60 constituting the tandem solar cell 200, the output (power) of the entire tandem solar cell 200 can be maximized.

The series-parallel circuits 95, 105, and 75 may be configured by positive and negative leads which are terminals of the solar cell array, but the series-parallel circuits 95, 105, and 75 may be switched by an electronic switch circuit in accordance with a change in the solar spectrum or incident light, and the number of series connections and the number of parallel connections may be changed to maximize the output. In each module 90, 100, 70, the solar cell array constituted by connecting a plurality of solar cells in parallel is connected in series by a lead wire, and therefore, even if a characteristic variation occurs in the plurality of solar cells, a current share is formed in accordance with the variation, and the output reduction of the module is minimized. In the conventional tandem solar cell, since only the planar photosensitive member is used, it is difficult to adjust the output current by series-parallel connection as in the tandem solar cell 200 of the present application.

In the tandem solar cell 200 described above, the cell group modules 90, 100, and 70 are stacked in this order from the upper side, and the planar photosensitive module 60 is disposed in the lowermost layer, and the center wavelength of the sensitivity wavelength band is disposed closer to the sunlight incidence side as the center wavelength becomes shorter. Therefore, the photoelectric conversion efficiency of the tandem solar cell 200 can be improved.

Since the cell group modules 90, 100, and 70 are incorporated in the upper 3 layers, the photosensitive module 60 is incorporated in the lowermost layer, and the reflected light reflected by the planar photosensitive module 60 is photoelectrically converted in the upper module. This is advantageous in this respect. In particular, since the module 60 is provided with the cold mirror 66 for reflecting light having a wavelength of 1100nm or shorter, which is easy to perform photoelectric conversion of the modules 90, 100, and 70, the cold mirror is advantageous in that the reflected light is effectively utilized to improve the photoelectric conversion efficiency. Since the cell group modules 90, 100, and 70 function as filters for the modules 100, 70, and 60 located below the modules, respectively, the modules located below the modules are less likely to overheat, which is advantageous in terms of improvement of photoelectric efficiency. As shown in fig. 14, by appropriately setting the sensitivity wavelength bands of the modules 90, 100, 70, and 60, it is possible to supply a wide range of light of the solar spectrum for photoelectric conversion, and it is possible to improve the photoelectric conversion efficiency of the tandem solar cell 200 to 50% or more.

Further, as shown in fig. 16, the series-parallel circuits 95, 105, and 75 are set so that the output current of each of the modules 90, 100, and 70 is equal to the output current of the module 60, and therefore, the power generation function of the tandem solar cell 200 can be sufficiently exhibited, and the photoelectric conversion efficiency can be improved.

Furthermore, the antireflection films 36, 46, and 17 are formed on the solar cells 30, 40, and 10 incorporated in the modules 90, 100, and 70, respectively, and the cells themselves reflect and diffuse incident light in an oblique direction to increase light absorption efficiency, and also increase light-blocking efficiency inside the tandem solar cell 200, thereby effectively contributing to improvement of photoelectric conversion efficiency.

In the modules 90, 100, and 70, the solar cells 30, 40, and 10 are arranged in 2 layers, and the solar cells 30, 40, and 10 are densely arranged in both the top view and the side view, so that the total area of pn junctions is large, and the photoelectric conversion efficiency is improved.

In addition, since the solar cells 30, 40, and 10 are arranged such that the direction of connecting the positive and negative electrodes is oriented in the horizontal direction, when light incident from the upper side enters each solar cell, the light is incident on the pn junction at least 2 times, and the photoelectric conversion efficiency is improved.

Further, since the solar cells 30, 40, and 10 incorporated in the modules 90, 100, and 70 can be independently manufactured, the degree of freedom in design and manufacturing is improved without being affected by the lattice constant of the semiconductor of another solar cell module or the like.

Next, the tandem solar cell 300 of example 2 will be described. Here, although the type of module used in the tandem solar cell 300 is partially different from that of the tandem solar cell 200, the structure is the same as that of the tandem solar cell 200, and thus the description is simplified.

Fig. 17 and 18 are cross-sectional views of a tandem solar cell 300 including 4 solar cell modules of 4 types, i.e., a GaAsP/GaP planar photosensitive module 50, a GaAlAs/GaAs cell group module 100, a silicon cell group module 70, and a germanium cell group module 80.

In the laminated solar cell 300, solar cell modules 50, 100, 70, 80 having different sensitivity wavelength bands to the spectrum of sunlight are stacked such that modules having shorter central wavelengths of the sensitivity wavelength bands are located closer to the sunlight incidence side. As is clear from fig. 19, the relationship between the sensitivity wavelength band center wavelengths of the solar cell modules 50, 100, 70, and 80 is: the center wavelength of the component 50 (about 450nm) < the center wavelength of the component 100 (about 700nm) < the center wavelength of the component 70 (about 800nm) < the center wavelength of the component 80 (about 1200 nm). Therefore, an aluminum nitride substrate 301 is disposed at the lowermost layer, and a germanium cell group module 80, a silicon cell group module 70, a GaAlAs/GaAs cell group module 100, and a GaAsP/GaP planar photosensitive module 50 are stacked in this order on the substrate and bonded together with a transparent adhesive, and then a transparent glass protective layer 304 is stacked on the uppermost layer where a photosensitive surface for receiving sunlight is formed and bonded together with a transparent adhesive.

Positive and negative leads 83 and 84 of module 80, positive and negative leads 73 and 74 of module 70, positive and negative leads 103 and 104 of module 100, and positive and negative leads 57a and 58a of module 50, respectively, extend to the outside of the modules to form a series-parallel circuit (not shown) of the respective modules.

In this tandem solar cell 300, the GaAsP/GaP planar photosensitive element 50 located closest to the incident side photoelectrically converts light in a short wavelength region, the light penetrating the element 50 is photoelectrically converted in the GaAiAs/GaAs solar cell 40 of the element 100 on the lower side thereof, the light penetrating the element 100 is photoelectrically converted in the silicon solar cell 10 of the element 70 on the lower side thereof, and the light in a long wavelength penetrating the element 70 is photoelectrically converted in the germanium solar cell 20.

On the lower side of the germanium solar cell 20, an aluminum nitride substrate 301 plated with an aluminum reflective film 302 is bonded and fixed by a transparent adhesive. The aluminum reflective film 302 acts to re-reflect light that passes between the upper solar cells and escapes and light that is reflected inside the module, reducing the fraction of sunlight that is not utilized.

As described with reference to fig. 15, reflection and scattering of light are also generated between the solar cells 40, 10, and 20 of the modules 100, 70, and 80, and light is also made incident on the lower sides of the solar cells and is subjected to photoelectric conversion. As described with reference to fig. 16, the optimum number of series and parallel connections of the series-parallel circuits of the respective modules 100, 70, 80 is also set in accordance with the output characteristics of the respective solar cells 40, 10, 20 so that the output currents of the modules 100, 70, 80 are equal to the output current of the module 50, respectively.

The tandem solar cell 300 described above also has basically the same operational advantages as the tandem solar cell 200, but the differences from the tandem solar cell 200 will be briefly described. The laminated solar cell 300 can be configured by effectively using the flat photosensitive element 50 mainly composed of GaAsP compound semiconductor having a wavelength band sensitive to a short wavelength region of the solar spectrum, which is difficult to configure a spherical solar cell. Further, the antireflection film 56 of the flat photosensitive member 50 formed on the uppermost layer enhances the internal light-blocking effect of the battery 300.

In the above-described embodiment, the planar photosensitive members 60, 50 are used for the high energy band on the short wavelength side or the low energy band on the long wavelength side of the solar spectrum. In the solar cell module of the compound semiconductor which realizes high photoelectric conversion in such a wavelength region, it is not necessary to use a spherical solar cell, and a planar photosensitive module which is easy to manufacture can be used, which is advantageous in terms of cost-benefit ratio.

Next, a tandem solar cell according to another embodiment is described.

As shown in fig. 20 and 21, the stacked solar cell 400 has the structure: cylindrical 2 types of solar cell modules 410 and 420 are stacked in a close contact manner in a concentric manner, and a transparent cylindrical body 401 made of thin transparent glass or synthetic resin is covered on the outermost layer, and a transparent cylindrical body 402 made of the same thin transparent glass or synthetic resin is also housed in the innermost layer.

A fluid passage 403 is formed in the center of the tandem solar cell 400, and heat is transferred from the cell 400 to the liquid or gas flowing through the fluid passage 403 to cool the tandem solar cell 400.

The inner solar cell module 410 is a germanium cell group module in which a plurality of germanium solar cells 20 are arranged in a plurality of rows and a plurality of columns to form a cylindrical shape. This is the same as the germanium battery group module 80 described above, which is formed in a cylindrical shape. The outer solar cell module 420 is a cylindrical GaAlAs/GaAs cell group module in which a plurality of GaAlAs/GaAs solar cells 40 are arranged in a plurality of rows and a plurality of columns. This is the same as the case where the GaAlAs/GaAs battery pack 100 is formed in a cylindrical shape.

In each module 410, 420, the positive and negative leads 404, 405 of each solar cell array extend outward from both ends of the module 410, 420, but each solar cell array is preferably arranged such that the line connecting the positive and negative electrodes of the solar cells 20, 80 is oriented in a direction orthogonal to the sunlight incidence direction.

In each of the solar cell modules 410 and 420, a series-parallel circuit is formed so that the output currents of the solar cell modules 410 and 420 are equal by connecting the plurality of solar cells 20 and 80 in series-parallel via positive and negative leads 404 and 405.

When sunlight is incident from the outside, the germanium cell group module 410 having a long center wavelength of the sensitivity wavelength band is disposed on the inside, and the GaAlAs/GaAs cell group module 420 having a short center wavelength of the sensitivity wavelength band is disposed on the outside.

This tandem solar cell 400 is a solar cell in which 2-layer solar cell modules 410 and 420 are stacked, and corresponds to a solar cell having a 4-layer structure for solar light incident from the upper side as indicated by an arrow; this cell 400 corresponds to a solar cell having 4 or more layers on both the left and right sides. Therefore, sunlight is frequently encountered in the solar battery cell, and the photoelectric conversion efficiency is improved.

Further, since the laminated solar cell 400 has a cylindrical outer shape, it has no directivity with respect to the incident direction of sunlight, and easily absorbs sunlight incident from various directions. Further, since the cooling can be performed by the fluid flowing through the internal fluid passage, the photoelectric conversion efficiency is improved, and the durability is also improved by suppressing the deterioration due to heat.

In the present embodiment, a solar cell having a 2-layer structure was described as an example, but a stacked solar cell having a cylindrical 3-layer structure, 4-layer structure, or 5-layer structure in which 3 or more kinds of cylindrical solar cell modules are stacked can also be realized.

Next, a conversion method of performing partial conversion of the above embodiment will be described.

(1) The types of solar cell modules incorporated in the tandem solar cell may be 2, or 3, 5 or more, but it is preferable that at least 1 type of solar cell module is constituted by a cell group module having a plurality of solar cells, and at least 1 type of solar cell module is constituted by a flat photosensitive module. Further, the modules arranged so that the shorter the center wavelength of the sensitivity wavelength band is, are located closer to the sunlight incidence side.

For example, 1 kind of flat photosensitive elements and 1 kind of cell group elements are provided, the flat photosensitive elements are disposed on the upper layer of the incident side, and the cell group elements are disposed on the lower layer. On the contrary, the cell assembly is disposed on the upper layer of the incident side, and the flat photosensitive element is disposed on the lower layer.

For example, 1 kind of flat photosensitive elements and 2 kinds of cell group elements are provided, and 1 flat photosensitive element is disposed on the upper layer of the incident side, 1 cell group element is disposed on the middle layer, and 1 cell group element is disposed on the lower layer. On the contrary, 1 battery group assembly is arranged on the upper layer, 1 battery group assembly is arranged on the middle layer, and 1 plane photosensitive assembly is arranged on the lower layer.

For example, 2 kinds of flat photosensitive elements and 2 kinds of cell group elements are provided, the 2 kinds of cell group elements are arranged in the middle layer, and the flat photosensitive elements are arranged in the upper layer and the lower layer, respectively, so that they are inserted in the upper and lower layers.

(2) A planar photosensitive module (solar cell module) disposed at the uppermost layer is configured by a semiconductor such as a gallium nitride (GaN) single crystal or a silicon carbide (SiC) single crystal that absorbs ultraviolet rays and generates electric power. In this case, since the power generation can be performed by effectively utilizing the ultraviolet rays having large light energy, not only can the photoelectric conversion efficiency of the tandem solar cell be improved, but also the deterioration of the lower solar cell module can be effectively suppressed by the ultraviolet rays.

(3) Solar cells can be manufactured using, as materials, amorphous semiconductors other than the above-described semiconductors, such as silicon, which can be photoelectrically converted, group III-V compound semiconductors (e.g., InGaN, InGaP, etc.), group II-VI compound semiconductors (e.g., ZnO, Cd — Te, etc.), and chalcogenide semiconductors containing group VI elements (S, Se, Te, etc.) (e.g., CuInGaSe 2).

(4) The battery group module constitutes a plurality of solar cell modules all incorporated in a laminated solar cell. In this case, a reflective film or a reflective member having a function of reflecting light is preferably provided on a lower portion or a lower surface of the lowermost solar cell module.

(5) A flexible laminated solar cell is formed by using a flexible transparent sheet instead of the above-described transparent glass protective layer 76 and hard materials such as the aluminum nitride substrates 201 and 301.

(6) Transparent insulating glass may be used instead of the transparent synthetic resin 75a of the above-described components 70, 80, 90, 100.

(7) Transparent glass or titanium dioxide (TiO) having a large refractive index is mixed into the light transmitting portion of the module 70, 80, 90, 100₂) And the like to improve the optical performance of the light transmitting portion.

Claims (17)

1. A laminated solar cell, which is formed by weaving a plurality of solar cell modules and laminating them into a single body,

containing a plurality of kinds of solar cell modules having different sensitivity wavelength bands, and stacking the solar cell modules such that the modules having the shorter center wavelengths of the sensitivity wavelength bands are located closer to the sunlight incidence side, and

at least one solar cell module is constituted by a cell group module having a plurality of substantially spherical solar cells arranged in a plurality of rows and a plurality of columns,

a series circuit for connecting the plurality of solar cell modules in series is provided, and

the output current of the plurality of types of solar cell modules is set to be equal to the output current of the solar cell module having the smallest output current.

2. The tandem solar cell according to claim 1,

at least one solar module is formed from a planar light-sensitive module having a planar common pn junction.

3. The tandem solar cell according to claim 1,

has 4 solar cell modules, wherein

3 types of solar cell modules were constituted by a cell group module having substantially spherical solar cells arranged in a plurality of rows and a plurality of columns, and 1 type of solar cell module was constituted by a planar photosensitive module having a planar common pn junction.

4. The tandem solar cell according to any one of claims 1 to 3,

the solar cells arranged in a plurality of rows and a plurality of columns in the plurality of cell group assemblies are electrically connected by a plurality of leads extending in the row direction or the column direction and led out to the outside.

5. The tandem solar cell according to claim 2 or 3,

each battery group component has

And a series-parallel circuit for connecting the battery group modules in series-parallel via the plurality of leads.

6. The tandem solar cell according to claim 5,

the series-parallel circuit of each battery group assembly is configured such that an output current of each battery group assembly is substantially equal to an output current of the planar photosensitive assembly.

7. The tandem solar cell according to claim 6,

each of the cell group modules has 2 layers of a plurality of spherical solar cells arranged in a plurality of rows and a plurality of columns on a plane, and the 2 layers of solar cells are arranged so as to be close to each other in a plan view without overlapping.

8. The tandem solar cell according to claim 2,

the planar photosensitive element is disposed at the lowermost layer so as to be located below the plurality of cell group elements, and a reflecting member capable of reflecting sunlight is provided on the planar photosensitive element.

9. The tandem solar cell according to claim 1,

in any solar cell module other than the solar cell module closest to the incident side in the incident direction of sunlight, a mirror film that reflects light in a sensitivity wavelength band that is easily absorbed by the solar cell module on the upper side thereof is formed on the surface of the solar cell module.

10. The tandem solar cell according to claim 1,

in the cell group module, a plurality of solar cells are embedded in transparent glass or a synthetic resin material.

11. The tandem solar cell according to claim 1,

a transparent member made of transparent glass or synthetic resin is bonded to the upper surface of the solar cell module closest to the incident side in the sunlight incident direction.

12. The tandem solar cell according to claim 3,

the planar photosensitive element is arranged at the lowest layer below the plurality of cell group elements, and the 3 kinds of cell group elements include 1 st to 3 rd cell group elements stacked in order from the sunlight incidence side,

the 1 st cell group module has a plurality of solar cells in which substantially spherical pn junctions are formed at substantially spherical GaP single crystal surface layers,

the 2 nd cell group module has a plurality of solar cells in which substantially spherical pn junctions are formed at substantially spherical GaAs single crystal surface layers,

the 3 rd cell group module includes a plurality of solar cells in which a substantially spherical pn junction is formed at a substantially spherical Si single crystal surface layer portion.

13. The tandem solar cell according to claim 12,

the planar photosensitive assembly has a planar common pn junction formed in an InGaAs semiconductor layer formed on an n-type InP semiconductor substrate.

14. The tandem solar cell according to claim 3,

the planar photosensitive element is arranged on the uppermost layer above the plurality of cell group elements, and the 3 kinds of cell group elements include 1 st to 3 rd cell group elements stacked in this order from the sunlight incidence side,

the 1 st cell group module has a plurality of solar cells in which substantially spherical pn junctions are formed at substantially spherical GaAs single crystal surface layers,

the 2 nd cell group module has a plurality of solar cells in which a substantially spherical pn junction is formed at a substantially spherical Si single crystal surface layer portion,

the 3 rd cell group module includes a plurality of solar cells in which a substantially spherical pn junction is formed at a substantially spherical Ge single crystal surface layer portion.

15. The tandem solar cell according to claim 14,

the planar photosensitive component has a planar common pn junction formed in a GaAsP semiconductor layer formed on an n-type GaP semiconductor substrate.

16. The tandem solar cell according to claim 2,

there are 2 kinds of flat photosensitive members, and 1 or more battery group members are interposed between the 2 kinds of flat photosensitive members.

17. The tandem solar cell according to claim 1,

the plurality of types of solar cell modules are composed of a plurality of cell group members formed in a cylindrical shape, and

the cell group assemblies are stacked in concentric circles.