TWI505479B - Optical absorption layer of thin-film solar cell and manufacturing method thereof - Google Patents

Description

Light absorbing layer of thin film solar cell and manufacturing method thereof

The present invention relates to a light absorbing layer of a thin film solar cell, and more particularly to a light absorbing layer of a thin film solar cell having a modulated film layer of three energy band segments and a method of fabricating the same.

Solar cells are one of the currently known environmentally friendly power sources, and solar cells based on germanium wafers must maintain a certain silicon wafer thickness (about 150 to 300 microns). In contrast, thin-film solar cells only need to use a very thin layer of optoelectronic material (about 1-3 microns), the material is very small, and the film structure can use a soft substrate, and the application flexibility is large. Semiconductor thin film solar cells are currently roughly classified into three types, namely, thin film (Silicon TF), cadmium telluride (CdTe), and copper indium gallium selenide (CIGS).

In thin-film solar cells, CuInSe ₂ (Copper Indium Diselenide) or CuIn _1-x Ga _x Se ₂ (Copper Indium Gallium Diselenide, also known as CIGS) belongs to Group I-III-VI. Compound semiconductor. These materials have excellent light absorption properties and material stability is also quite good. In terms of energy conversion efficiency, if the concentrating device is used, the current battery efficiency has reached 30%, and it has reached 20.3% under the AM1.5 standard environmental test, which is comparable to the performance of the solar cell component of the same crystal structure. In the large-area process, the optimum conversion efficiency of the flexible plastic substrate has reached 14.1%. Due to its excellent stability and conversion efficiency, it is considered to be the most promising thin film solar cell.

At present, CIGS processes mainly include co-evaporation and selenization. Co-evaporation can obtain a CIGS film with a concentration gradient of gallium (Ga), which means that there is a V-type energy gap distribution in the CIGS film, which contributes to the effective absorption of light and the collection of carriers. Because the growth rate of the co-deposited film is slow and has good material properties, a solar cell with higher efficiency can be produced, but the slow growth rate also leads to a low process yield and a relatively high cost; and the selenization process It is divided into two stages, that is, the pre-plating of the precursor is first plated and then heated and reacted. The plated precursor may be layered and plated with a metal element of the composition, and the thickness of each layer is appropriately adjusted according to the required composition, if heated in a selenium vapor or H ₂ Se gas stream at a slow temperature for a long time, for example, 500 ° C, In 30 minutes, a film with excellent material quality can be obtained; another method of selenization is called Rapid Thermal Selenization, which is to further deposit a layer of selenium on the pre-plated structure of the multilayer precursor as part of the precursor. The precursor structure can be applied with rapid temperature rise (greater than 10 ° C / sec), for example, 500 ° C, 1 minute, so that the reaction can be completed in a short time, and the pre-coating of the precursor can be used in various large-area or even low-cost processes, such as Sputtering, ink printing or electroplating, etc., has the cost advantage of mass production.

However, a CIGS film with a V-type energy gap distribution was prepared using a rapid selenization method. There are substantial difficulties, and because of the rapid reaction speed of the process, it is difficult to obtain a CIGS film with good properties, so the photoelectric conversion efficiency is poor. In addition, Ga and Se are costly elements and do not have a cost advantage in mass production.

For the above reasons, it is necessary to provide a thin film solar cell light absorbing layer and The manufacturing method is to solve the problems existing in the conventional technology.

SUMMARY OF THE INVENTION A primary object of the present invention is to provide a light absorbing layer of a thin film solar cell having three band segments to improve the photoelectric conversion efficiency of the light absorbing layer.

A secondary object of the present invention is to provide a light absorbing layer of a thin film solar cell which replaces Ga and Se of a conventional light absorbing layer CIGS film with an easily obtainable and low cost element such as aluminum (Al) and sulfur (S). Reduce manufacturing costs and increase their economic competitiveness.

Another object of the present invention is to provide a method for producing a light absorbing layer of a thin film solar cell, which is suitable for use in a rapid selenization method, which can shorten the reaction time and produce a light absorbing layer of a thin film solar cell excellent in quality, thereby increasing the amount Production advantage.

To achieve the above object, the present invention provides a light absorbing layer of a thin film solar cell comprising a modulation film layer composed of a semiconductor compound having a copper indium selenide (CuInSe ₂ ) single composition film layer and formed Three energy bands.

In one embodiment of the present invention, the structure of the modulation film layer is as follows: CuInS _y Se _2-y /CuInSe ₂ /CuIn _1-x Al _x Se ₂ , wherein x<1, y<2.

In an embodiment of the invention, the gradient of the conduction band energy of the adjacent band segments is different.

In one embodiment of the present invention, the copper indium sulfur selenide _{(CuInS y Se 2-y)} , thickness of the copper indium diselenide (CuInSe ₂₎ aluminum and copper indium selenide _{(CuIn 1-x Al x Se} 2) of 0.3 Micron to 0.9 micron, 0.5 micron to 1.5 micron, and 0.2 micron to 0.6 micron.

In one embodiment of the invention, the thickness of the modulating film layer is between 1 micron and 3 microns.

In one embodiment of the invention, when the modulating film layer has three band segments, the energy band of the intermediate band segment is between 0.90 and 1.10 eV.

The invention further provides a method for manufacturing a light absorbing layer of a thin film solar cell, comprising the steps of: (1) providing an element and a selenide stack as a precursor, having aluminum (Al) / indium selenide (In-Se) / a sequence of copper selenide (Cu-Se) / selenium (Se); (2) rapidly heating the element and the selenide laminated precursor to 600 ° C at a temperature of 10 ° C or more per second, maintaining the temperature for a predetermined time; 3) cooling to room temperature to produce a selenide film having a copper indium selenide (CuInSe ₂ ) single composition film layer and a copper indium aluminum selenide (CuIn _1-x Al _x Se ₂ ) gradient film layer And (4) providing a sulfur vapor and heating to above 400 ° C to vulcanize the selenide film to form a copper indium sulphide (CuInS _y Se _2-y ) graded film layer; the light absorbing layer of the above procedure is completed; A modulation film layer structure is included as follows: CuInS _y Se _2-y /CuInSe ₂ /CuIn _1-x Al _x Se ₂ , wherein x<1, y<2, and the modulation film layer has three energy bands Section.

In an embodiment of the invention, the predetermined time of step (2) is 30 seconds or more.

In an embodiment of the invention, the aluminum concentration gradient of the selenized film is by the The thickness of the element stack precursor and the temperature control of the rapid heating.

In one embodiment of the present invention, the thickness of aluminum (Al)/indium selenide (In-Se)/copper selenide (Cu-Se)/selenium (Se) in the precursor is 100 nm, respectively. /200 nm / 550 nm / 1000 nm.

In an embodiment of the invention, steps (2) through (5) are both carried out in a passive atmosphere.

In one embodiment of the invention, the sulfur content of the modulating film layer is controlled by the amount of sulfur vapor introduced.

A‧‧‧ Conduction band energy curve

B‧‧‧Price band energy curve

Fig. 1 is a schematic view showing the energy band structure of a light absorbing layer of a thin film solar cell according to a first embodiment of the present invention.

Fig. 2 is a graph showing a change in concentration gradient of aluminum content in a method for producing a light absorbing layer of a thin film solar cell according to a second embodiment of the present invention.

Fig. 3 is a graph showing a change in concentration gradient of sulfur content in a method for producing a light absorbing layer of a thin film solar cell according to a second embodiment of the present invention.

The above and other objects, features and advantages of the present invention will become more <RTIgt; Furthermore, the directional terms mentioned in the present invention, such as upper, lower, top, bottom, front, rear, left, right, inner, outer, side, surrounding, central, horizontal, horizontal, vertical, longitudinal, axial, Radial, uppermost or lowermost, etc., only refer to the direction of the additional schema. Therefore, the directional terminology used is for the purpose of illustration and understanding of the invention.

The light absorbing layer of the thin film solar cell of the first embodiment of the present invention comprises a modulation film layer, and the structure of the modulation film layer can be expressed by the following formula: CuInS _y Se _2-y /CuInSe ₂ /CuIn _{1- x} Al _x Se ₂ , wherein x<1, y<2. Please refer to Figure 1 for a schematic diagram of the conduction band of the modulation film layer.

1 is a schematic view showing the energy band structure of a light absorbing layer of a thin film solar cell according to a first embodiment of the present invention, wherein A represents a valence band energy curve, B represents a conduction band energy curve, and a gap between A and B represents an energy gap. The solid line part is the energy curve of the original copper indium selenide (CuInSe ₂ , CIS for short) film, and the broken line part is the change of the conduction band and the valence band of the modulation film layer in the invention. In the first figure, near the back electrode (Mo), a portion of CuIn _1-x Al _x Se ₂ (CIAS) in the modulation film layer is formed by the addition of aluminum in the CIS film structure, so that conduction The slope of the band with the energy curve B changes, from the solid line to the dotted line, which helps to let the electrons leave, thus reducing the chance that the hole will be recombined again. Close to the buffer layer, such as CdS in Fig. 1, the formation of CuInS _y Se _2-y (CISSe) in the modulation layer due to the addition of sulfur affects the conduction band energy curve. B, the conduction band energy curve B is changed from the solid line to the dotted line in the figure, which reduces the discontinuity of the conduction band energy curve B between the original CISSe and CdS, which is beneficial to the transmission of electrons; the addition of sulfur also affects The slope of the valence band energy curve A makes its conductive properties close to those of the intrinsic semiconductor, and can extend the range of the depletion region, which is beneficial to the absorption of light. Furthermore, an n-type structure has been formed near the CdS, so that the position of the pn junction is moved into the structure of the modulation film layer, which can reduce the influence of the CdS/CISSe interface defect.

According to a preferred embodiment of the present invention, the light absorbing layer comprises a modulation film layer consisting of copper indium sulphide (CuInS _y Se _2-y ), copper indium selenide (CuInSe ₂ ), and copper indium aluminum selenide (CuIn _1-x Al _x Se ₂ ) is formed in sequence, which can be formed due to the graded film structure of CuInS _y Se _2-y and CuIn _1-x Al _x Se ₂ An energy band segment having the above effects. In a preferred embodiment of the invention, when the modulation film layer has three energy band segments, the conduction band energy changes to different three-stage gradients. The thickness of the modulating film layer is between 1 micrometer and 3 micrometers. The thicknesses of the copper indium sulphide (CuInS _y Se _2-y ), copper indium selenide (CuInSe ₂ ), and copper indium aluminum selenide (CuIn _1-x Al _x Se ₂ ) are respectively 0.3 micrometers to 0.9 micrometers, 0.5 micrometers to 1.5 millimeters. Micron, 0.2 microns to 0.6 microns. In addition, the energy gaps of the copper indium sulphide (CuInS _y Se _2-y ), copper indium selenide (CuInSe ₂ ), and copper indium aluminum selenide (CuIn _1-x Al _x Se ₂ ) film structures are respectively 1.20 to 1.30 eV. , about 1.00 eV and 1.35 to 1.50 eV, which may be, for example, 1.30 eV/1.03 eV/1.40 eV.

Manufacturer of light absorbing layer of thin film solar cell according to second embodiment of the present invention The first method is to provide an elemental and selenide laminate precursor having a film sequence of aluminum/copper/indium/selenium. In this step, the element and the selenide stack are precursors, and may be formed on the substrate on which the back electrode layer is plated using a material such as copper selenide/indium selenide/aluminum or copper selenide/indium selenide. The back electrode layer may be, for example, molybdenum (Mo).

A method of producing a light absorbing layer of a thin film solar cell according to a second embodiment of the present invention is followed by rapidly heating the element laminated precursor at a temperature of 10 ° C or more per second. In this step, the heating program is heated from room temperature to 10 ° C per second or higher, and can be heated to, for example, 15 ° C per second to 600 ° C, maintaining the temperature for at least 30 seconds, and reacting in a rapid heating manner to form CuIn _1-x Al _x Se ₂ (CIAS) compound, this step is called rapid selenization.

Manufacturer of light absorbing layer of thin film solar cell according to second embodiment of the present invention The process is followed by cooling to room temperature to produce a selenide film. In this step, the aluminum concentration gradient of the selenized film can be controlled by the thickness of the element stack precursor and the reaction temperature. The aluminum concentration gradient affects the structure of the film near the back electrode layer, which in turn affects the slope of its conduction band energy. In a preferred embodiment of the present invention, the thickness of aluminum (Al) / indium selenide (In-Se) / copper selenide (Cu - Se) / selenium (Se) in the precursor is 100 nm, respectively. /200 nm / 550 nm / 1000 nm. While the reaction temperature is preferably as described above in the rapid selenization step, it is controlled at about 600 °C. Please refer to Figure 2 for the gradient of aluminum concentration gradient.

As can be seen from Fig. ₂ , the aluminum concentration between CIS and CuIn _0.7 Al _0.3 Se ₂ forms a gradient change, and part of the indium has been replaced by aluminum, but most of the other components in the film layer are still CIS.

A method of producing a light absorbing layer of a thin film solar cell according to a second embodiment of the present invention is followed by providing a sulfur vapor to the selenized film. In this step, the selenized film is preferably placed in a passive atmosphere and passed through a sulfur vapor, which may be, for example, 5.5 x ^{10 15} atoms/cm 2 per second. The passive atmosphere can be, for example, nitrogen or argon.

A method for producing a light absorbing layer of a thin film solar cell according to a second embodiment of the present invention is followed by heating to 400 ° C or higher to form a modulation film layer having a chemical composition such as the following formula: CuInS _y Se _2-y /CuInSe ₂ /CuIn _1-x Al _x Se ₂ wherein x<1, y<2, and the film layer has three energy band segments, each band segment having different conduction band energy gradient. In this step, the temperature of the heating may also be, for example, 450 ° C, and maintained at this temperature for about 5 minutes. The sulfur concentration gradient affects the structure of the film near the buffer layer, which in turn affects the slope of its conduction band and valence band. In a preferred embodiment of the present invention, the concentration gradient of the sulfur content of the modulated membrane layer is controlled by the amount of sulfur vapor introduced, and if the sulfur is introduced, the sulfurization reaction time can be greatly shortened. Please refer to Figure 3 for the sulfur concentration gradient change chart. As can be seen from Figure 3, part of the selenium has been replaced by sulfur.

The light absorbing layer of the thin film solar cell provided by the embodiment of the present invention and the method of manufacturing the same can reduce the production cost by using aluminum instead of gallium, and use pure sulfur vapor instead of sulfide gas during the vulcanization process, for example, H ₂ S, therefore less toxic and the reaction temperature can be reduced to 450 ° C, the process time is shortened to less than 5 minutes, because of the short process time, low cost and high output characteristics, and can be applied to glass or flexible substrates, Also suitable for in-line or roll-to-roll production lines.

The present invention has been disclosed in its preferred embodiments, and is not intended to limit the invention, and the present invention may be modified and modified without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application.

A‧‧‧ valence band energy curve

B‧‧‧Transmission band energy curve

Claims (11)

A light absorbing layer of a thin film solar cell, comprising a modulating film layer having a single composition film layer of copper indium selenide (CuInSe ₂ ) and forming three energy band segments, the modulating film layer The chemical composition is as follows: CuInS _y Se _2-y /CuInSe ₂ /CuIn _1-x Al _x Se ₂ , where x<1, y<2. The light absorbing layer of the thin film solar cell of claim 1, wherein the energy band gradient of the adjacent band segments is different. The light absorbing layer of the thin film solar cell of claim 1, wherein the copper indium sulphide (CuInS _y Se _2-y ), copper indium selenide (CuInSe ₂ ), and copper indium aluminum selenide (CuIn _1-x) The thickness of Al _x Se ₂ ) is 0.3 μm to 0.9 μm, 0.5 μm to 1.5 μm, and 0.2 μm to 0.6 μm, respectively. The light absorbing layer of the thin film solar cell of claim 1, wherein the modulating film layer has a thickness of from 1 micrometer to 3 micrometers. The light absorbing layer of the thin film solar cell of claim 1, wherein when the modulating film layer has three band segments, the energy band of the intermediate band segment is between 0.90 and 1.10 eV. between. A method for producing a light absorbing layer of a thin film solar cell, comprising the steps of: (1) providing an element and a selenide laminated precursor having aluminum (Al) / indium selenide (In-Se) / copper selenide (Cu) -Se)/Selenium (Se) film layer sequence; (2) rapidly heating the element and the selenide laminate precursor to 600 ° C at a temperature of 10 ° C or higher per second to maintain the temperature for a predetermined time; (3) cooling to room temperature To produce a selenide film consisting of a single layer of copper indium selenide (CuInSe ₂ ) and a layer of copper indium aluminum selenide (CuIn _1-x Al _x Se ₂ ) gradient film; and (4) Providing a sulfur vapor and heating to 400 ° C or higher to vulcanize the selenized film to form a copper indium sulphide (CuInS _y Se _2-y ) gradation film layer; wherein the light absorbing layer comprises a modulating film The layer structure is as follows: CuInS _y Se _2-y /CuInSe ₂ /CuIn _1-x Al _x Se ₂ , where x<1, y<2, and the modulation film layer has three energy band segments. The method for producing a light absorbing layer of a thin film solar cell according to claim 6, wherein the predetermined time of the step (2) is 30 seconds or longer. The method for producing a light absorbing layer of a thin film solar cell according to claim 6, wherein the aluminum concentration gradient of the selenized film is controlled by a thickness of the element laminated precursor and a temperature of the rapid heating. The method for producing a light absorbing layer of a thin film solar cell according to claim 6, wherein the element and the selenide laminated precursor are aluminum (Al)/indium selenide (In-Se)/copper selenide ( The thickness of Cu-Se)/selenium (Se) is 100 nm/200 nm/550 nm/1000 nm, respectively. The method for producing a light absorbing layer of a thin film solar cell according to claim 6, wherein the steps (2) to (4) are each carried out in a passive atmosphere. The method for producing a light absorbing layer of a thin film solar cell according to claim 6, wherein the sulfur content of the modulating film layer is controlled by a sulfur vapor permeation amount.