Cadmium telluride thin-film solar cell and high-temperature doping method thereof

Abstract

The invention provides a cadmium telluride thin-film solar cell and a high-temperature doping method thereof, and the method comprises the steps: coating a wet film containing a doping substance on the surface of one side of a cadmium telluride absorption layer, and obtaining an ex-situ doped cadmium telluride absorption layer after high-temperature annealing. Wherein the doping substance comprises a V-group element fluoride, and the temperature of high-temperature annealing is greater than or equal to 200 DEG C. According to the cadmium telluride thin-film solar cell, the V-group element fluoride is adopted to carry out high-temperature doping at the temperature of 200 DEG C or above on the cadmium telluride absorption layer, the effective doping concentration is improved, meanwhile, the service life of a photon-generated carrier is considered, finally, the open-circuit voltage and the photoelectric conversion efficiency of the cadmium telluride thin-film solar cell are improved, and large-scale application and popularization are facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of solar cells and relates to a cadmium telluride thin film solar cell, in particular to a cadmium telluride thin film solar cell and a high temperature doping method thereof. Background Art

[0002] As the second generation of compound thin film solar cells, cadmium telluride (CdTe) thin film solar cells have the advantages of high efficiency and stability. In addition, this type of thin film solar cell has fast deposition speed, high production efficiency and relatively low cost, and has the basic conditions for large-scale mass production.

[0003] At present, the market prospects of thin-film solar cells are broad, especially photovoltaic building integration (BIPV) has a potential market value of hundreds of billions of yuan. In addition, the theoretical photoelectric conversion efficiency of CdTe thin-film solar cells is as high as 32%, which will make it competitive in conversion efficiency in the future. However, the highest photoelectric conversion efficiency of existing CdTe thin-film solar cells is 23.1% (First Solar), which is far lower than its theoretical maximum photoelectric conversion efficiency. The main reasons for the low photoelectric conversion efficiency of CdTe thin-film solar cells are: shorter photogenerated carrier lifetime and lower P-type doping concentration. CdTe thin film is a polycrystalline semiconductor film with highly complementary donors and acceptors, which makes its effective P-type doping concentration low, thus limiting the increase of its open circuit voltage.

[0004] In the past 30-40 years, Cu has been proven to be an acceptor that can effectively increase the doping concentration of CdTe. For example, CN109980026A discloses a copper-doped high-efficiency cadmium telluride nanocrystalline solar cell and its preparation method, which specifically comprises: after CdTe is deposited, a back contact layer containing Cu is deposited on its back; then, by annealing, Cu is diffused into CdTe to achieve Cu doping of CdTe and increase its effective carrier concentration.

[0005] However, using Cu doping to increase the doping concentration of CdTe has considerable limitations. On the one hand, there is an obvious upper limit to the increase in CdTe carrier concentration by Cu doping, which can only increase the CdTe carrier concentration to about 10 14 cm -3 Compared with other high-efficiency thin-film solar cells, such as copper indium gallium selenide (CIGS), the carrier concentration is about 10 16 cm -3 , which is 2 orders of magnitude lower. This also makes it difficult for the open circuit voltage of Cu-doped CdTe solar cells to be higher than 900mV, thus limiting the improvement of their photoelectric conversion efficiency. On the other hand, Cu doping has unstable defects, which can easily accelerate the decay rate of the photoelectric conversion efficiency of CdTe solar cells, and ultimately reduce the service life of the components.

[0006] To solve the above problems, technicians use more stable group V elements to dope CdTe, which has become one of the effective methods to improve the conversion efficiency and stability of CdTe solar cells. However, group V elements have higher doping activation energy than Cu, which requires higher temperatures to ionize, thereby producing effective doping to increase the carrier concentration of the CdTe layer. Otherwise, low-temperature annealing will result in too low an activation ratio of the doping elements.

[0007] It can be seen that how to provide a cadmium telluride thin-film solar cell and a high-temperature doping method thereof, increase the effective doping concentration of CdTe while not reducing or even increasing the lifetime of photogenerated carriers, and ultimately improve the open circuit voltage and photoelectric conversion efficiency of the CdTe solar cell, has become a problem that technical personnel in this field urgently need to solve. Summary of the invention

[0008] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a cadmium telluride thin film solar cell and a high-temperature doping method thereof, wherein the cadmium telluride absorption layer is doped with fluorides of group V elements at a high temperature of more than 200°C, thereby increasing the effective doping concentration while taking into account the lifetime of photogenerated carriers, and ultimately improving the open circuit voltage and photoelectric conversion efficiency of the cadmium telluride thin film solar cell, which is conducive to large-scale promotion and application.

[0009] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a high-temperature doping method for a cadmium telluride thin-film solar cell, comprising: coating a wet film containing a doping substance on one side of a cadmium telluride absorption layer, and obtaining a non-in-situ doped cadmium telluride absorption layer after high-temperature annealing. The doping substance comprises a fluoride of a group V element, and the temperature of the high-temperature annealing is ≥ 200°C.

[0011] The present invention adopts fluorides of group V elements to perform high-temperature doping on the cadmium telluride absorption layer. Since the fluorides of group V elements have a relatively high melting point, high-temperature annealing can be performed at a temperature above 200° C., thereby increasing the activation ratio of the group V elements and making up for the defect of insufficient annealing of chlorides of group V elements used in the conventional method. The effective doping concentration is increased while taking into account the lifetime of photogenerated carriers, thereby ultimately increasing the open circuit voltage and photoelectric conversion efficiency of the cadmium telluride thin-film solar cell, which is conducive to large-scale promotion and application.

[0012] Preferably, the group V element fluoride includes any one of SbF3, BiF3 or AsF3, or a combination of at least two of them, and more preferably SbF3 or AsF3, or a combination of SbF3 and BiF3, or a combination of BiF3 and AsF3.

[0013] Preferably, the concentration of the group V element fluoride in the wet film is 1-1000 mg / L.

[0014] Preferably, the solvent in the wet film includes water or an organic solvent.

[0015] Preferably, the organic solvent includes any one of methanol, ethanol or propanol, or a combination of at least two of them.

[0016] Preferably, the high temperature annealing temperature is 200-600°C.

[0017] Preferably, the high temperature annealing time is 1-60 min.

[0018] Preferably, the high temperature annealing method includes any one of furnace annealing, laser annealing or flash annealing.

[0019] Preferably, the high temperature annealing is performed in an atmosphere of air or protective gas.

[0020] Preferably, the protective gas comprises nitrogen and / or an inert gas.

[0021] Preferably, the wet film is coated by any one of spray coating, spin coating or blade coating.

[0022] Preferably, the wet film is dried before high-temperature annealing.

[0023] Preferably, the cadmium telluride absorption layer is sequentially cooled, cleaned and dried after high-temperature annealing.

[0024] Preferably, the cooling comprises natural cooling in an atmosphere of air or protective gas.

[0025] In a second aspect, the present invention provides a cadmium telluride thin-film solar cell, comprising a stacked glass substrate, a transparent conductive oxide layer, a window layer, an absorption layer, a back contact layer and a back electrode layer, wherein the absorption layer is non-in-situ doped with group V element fluorides using the high-temperature doping method described in the first aspect.

[0026] Preferably, the carrier concentration of the cadmium telluride thin film solar cell is ≥5×10 15 cm -3 , minority carrier lifetime ≥ 20ns, open circuit voltage ≥ 850mV.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention adopts fluorides of group V elements to perform high-temperature doping on the cadmium telluride absorption layer. Since the fluorides of group V elements have a relatively high melting point, high-temperature annealing can be performed at a temperature above 200° C., thereby increasing the activation ratio of the group V elements and making up for the defect of insufficient annealing of chlorides of group V elements used in the conventional method. The effective doping concentration is increased while taking into account the lifetime of photogenerated carriers, thereby ultimately increasing the open circuit voltage and photoelectric conversion efficiency of the cadmium telluride thin-film solar cell, which is conducive to large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a schematic diagram of the structure of a cadmium telluride thin film solar cell prepared by the high temperature doping method provided by the present invention.

[0030] Wherein: 101 - glass substrate; 102 - transparent conductive oxide layer; 103 - window layer; 104 - absorption layer; 105 - back contact layer; 106 - back electrode layer. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0032] An embodiment of the present invention provides a high-temperature doping method for a cadmium telluride thin-film solar cell, comprising: coating a wet film containing a doping substance on one surface of a cadmium telluride absorption layer, and obtaining a non-in-situ doped cadmium telluride absorption layer after high-temperature annealing, wherein the doping substance includes a fluoride of a group V element, and the temperature of the high-temperature annealing is ≥200°C.

[0033] The present invention adopts fluorides of group V elements to perform high-temperature doping on the cadmium telluride absorption layer. Since the fluorides of group V elements have a relatively high melting point, high-temperature annealing can be performed at a temperature above 200° C., thereby increasing the activation ratio of the group V elements and making up for the defect of insufficient annealing of chlorides of group V elements used in the conventional method. The effective doping concentration is increased while taking into account the lifetime of photogenerated carriers, thereby ultimately increasing the open circuit voltage and photoelectric conversion efficiency of the cadmium telluride thin-film solar cell, which is conducive to large-scale promotion and application.

[0034] In the present invention, the increase in the effective doping concentration of CdTe means the increase in the carrier concentration, which can effectively increase the hole concentration and move the hole Fermi level down to a position closer to the valence band; the increase in the lifetime of photogenerated carriers in CdTe can increase the photogenerated electron concentration and move the electron Fermi level up to a position closer to the bottom of the conduction band.

[0035] Therefore, the improvement of CdTe effective doping concentration and photogenerated carrier lifetime can promote the Fermi level splitting of CdTe solar cells, which will help to increase the open circuit voltage of solar cells and thus improve the photoelectric conversion efficiency of solar cells.

[0036] In some embodiments, the temperature of the high temperature annealing is ≥200°C, for example, it can be 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C or 600°C, and is more preferably 200-600°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] In certain embodiments, the group V element fluoride includes any one of SbF3, BiF3 or AsF3, or a combination of at least two of them. Typical but non-limiting combinations include a combination of SbF3 and BiF3, a combination of BiF3 and AsF3, a combination of SbF3 and AsF3, or a combination of SbF3, BiF3 and AsF3, and more preferably a combination of at least two of SbF3, BiF3 or AsF3.

[0038] Compared with other group V element fluorides, the present invention particularly prefers SbF3 or AsF3, or a combination of SbF3 and BiF3, or a combination of BiF3 and AsF3, because: BiF3 can effectively increase the minority carrier lifetime of CdTe, thereby increasing the open circuit voltage of CdTe solar cells; but due to the higher doping activation energy of Bi, the further increase of CdTe carrier concentration is limited. Compared with Bi, As and Sb require lower doping activation energy, which can more effectively increase the carrier concentration of CdTe. In addition, the use of AsF3 or a combination of SbF3 and BiF3 can more effectively ensure that the carrier concentration and minority carrier lifetime of CdTe are increased at the same time.

[0039] In some embodiments, the concentration of the group V element fluoride in the wet film is 1-1000 mg / L, for example, it can be 1 mg / L, 10 mg / L, 100 mg / L, 200 mg / L, 300 mg / L, 400 mg / L, 500 mg / L, 600 mg / L, 700 mg / L, 800 mg / L, 900 mg / L or 1000 mg / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] In CdTe thin-film solar cells, the concentration of group V fluorides as dopants has a significant impact on the performance of the cell. On the one hand, an appropriate concentration range can ensure that the dopant is evenly distributed in the CdTe film, thereby achieving effective P-type doping and increasing the carrier concentration and open-circuit voltage of the cell. On the other hand, an appropriate concentration can avoid over-doping, thereby effectively reducing the number of deep recombination centers formed by the dopant.

[0041] The present invention can optimize the electrical properties of the CdTe film by precisely controlling the concentration of the group V element fluoride, thereby improving the photoelectric conversion efficiency of the solar cell. In particular, within the concentration range of 1-1000 mg / L, a higher hole concentration and a longer carrier lifetime can be achieved, which is crucial to improving battery performance.

[0042] In certain embodiments, the solvent in the wet film includes water or an organic solvent.

[0043] In certain embodiments, the organic solvent comprises any one of methanol, ethanol or propanol or a combination of at least two thereof, typical but non-limiting combinations comprising a combination of methanol and ethanol, a combination of ethanol and propanol, a combination of methanol and propanol, or a combination of methanol, ethanol and propanol.

[0044] In some embodiments, the high temperature annealing time is 1-60 min, for example, it can be 1 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] In semiconductor manufacturing, precise control of annealing time is critical to achieve ideal doping activation. The present invention can ensure effective diffusion and activation of group V element fluorides in CdTe thin films by limiting the annealing time to 1-60 minutes, thereby achieving the required doping concentration. At the same time, it avoids excessive diffusion of group V elements due to too long annealing time, thereby forming deep recombination centers of carriers.

[0046] In some embodiments, the high temperature annealing method includes any one of furnace annealing, laser annealing or flash annealing.

[0047] In the present invention, the furnace annealing is a traditional annealing method, which can achieve uniform heating of the entire battery cell and is suitable for processing processes with high uniformity requirements; the laser annealing uses laser as a heat source to concentrate high energy in a small area to achieve rapid heating of the battery cell, and can accurately adjust the heating area and heating intensity; the flash annealing uses a high-power flash lamp for annealing, which can heat the battery cell to the target temperature in a very short time (milliseconds).

[0048] In the present invention, the furnace annealing, laser annealing and flash annealing are all conventional annealing methods in the art. As long as high temperature annealing of the cell can be achieved, the specific steps and process parameters of the various annealing methods are not particularly limited.

[0049] In some embodiments, the high temperature annealing is performed in an atmosphere of air or a protective gas.

[0050] In certain embodiments, the protective gas includes nitrogen and / or an inert gas.

[0051] In some embodiments, the wet film is coated by any one of spray coating, spin coating or blade coating.

[0052] In some embodiments, the wet film is subjected to a drying process before the high-temperature annealing to fully evaporate the solvent in the wet film.

[0053] In some embodiments, the cadmium telluride absorber layer is sequentially cooled, cleaned, and dried after high-temperature annealing.

[0054] In the present invention, the cleaning is performed using ultrapure water to fully remove excess fluoride of group V elements on the surface of the battery cell; the drying is specifically performed by fully drying the battery cell using compressed air or nitrogen.

[0055] In certain embodiments, the cooling includes natural cooling in an atmosphere of air or protective gas.

[0056] A certain embodiment of the present invention provides a cadmium telluride thin-film solar cell, comprising a stacked glass substrate, a transparent conductive oxide layer, a window layer, an absorption layer, a back contact layer and a back electrode layer, wherein the absorption layer is non-in-situ doped with group V element fluorides using the above-mentioned high-temperature doping method.

[0057] In some embodiments, the carrier concentration of the cadmium telluride thin film solar cell is ≥5×10 15 cm -3 , for example, it can be 5×10 15 cm -3 , 5.5×10 15 cm -3 , 6×1015 cm -3 , 6.5×10 15 cm -3 ,7×10 15 cm -3 , 7.5×10 15 cm -3 , 8×10 15 cm -3 , 8.5×10 15 cm -3 ,9×10 15 cm -3 , 9.5×10 15 cm -3 or 10 16 cm -3 , minority carrier lifetime ≥ 20ns, for example, it can be 20ns, 22ns, 24ns, 26ns, 28ns, 30ns, 32ns, 34ns, 36ns, 38ns or 40ns, open circuit voltage ≥ 850mV, for example, it can be 850mV, 875mV, 900mV, 925mV, 950mV, 975mV or 1000mV, but is not limited to the listed values, other unlisted values ​​within the numerical range are also applicable.

[0058] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0059] Example 1

[0060] This embodiment provides a high temperature doping method for a cadmium telluride thin film solar cell, which specifically includes the following steps:

[0061] (1) Prepare a 10 mg / L SbF3 aqueous solution as follows:

[0062] (1.1) Using clean weighing paper and an analytical balance, weigh 1 mg of SbF3 into a clean plastic beaker;

[0063] (1.2) Use a clean plastic measuring cylinder to weigh 50 mL of ultrapure water and pour it into the plastic beaker containing SbF3 in (1.1);

[0064] (1.3) Use a plastic rod to stir the solution thoroughly to completely dissolve SbF3;

[0065] (1.4) Pour the solution obtained in (1.3) into a 100 mL plastic volumetric flask;

[0066] (1.5) Use a small amount of ultrapure water in the plastic beaker (1.2) to rinse the plastic rod (1.3) and the inner wall of the plastic beaker. Pour the rinsed solution into the plastic volumetric flask (1.4). Repeat the above steps 3 times.

[0067] (1.6) Use a measuring cylinder and a pipette to add ultrapure water to the plastic volumetric flask in (1.5) and make up to 100 mL.

[0068] (2) Spraying a wet film on one side of the cadmium telluride absorption layer, specifically:

[0069] (2.1) Place the atomization equipment (Fulin-W001) and the sealed atomization chamber in a fume hood;

[0070] (2.2) Open the mist chamber, place the CdTe film sample in the center and then close the mist chamber;

[0071] (2.3) Place a sufficient amount of the 10 mg / L SbF3 aqueous solution obtained in (1) into the atomizing device;

[0072] (2.4) Turn on the atomization equipment and generate sufficient mist with a droplet size of 4.1 mm in the mist chamber at a rate of 3.3 mL / min;

[0073] (2.5) Keep the CdTe film sample in the mist for 5 minutes.

[0074] (3) Drying treatment, specifically:

[0075] The sprayed sample was transferred to a heating table at 80°C and heated for 10 min to fully dry.

[0076] (4) High temperature annealing, specifically:

[0077] (4.1) Raise the temperature of the tubular annealing furnace to 420°C;

[0078] (4.2) Introduce dry air into the tube furnace;

[0079] (4.3) After 10 minutes, place the dried sample in a graphite boat and push it into the center of the tube furnace;

[0080] (4.4) After 20 min, take the sample out of the tube furnace and allow it to cool naturally to room temperature in a dry air atmosphere.

[0081] (5) Post-processing, specifically:

[0082] The surface of the annealed sample was rinsed with sufficient ultrapure water to remove residual SbF3, and then fully dried with dry nitrogen.

[0083] Example 2

[0084] This embodiment provides a high temperature doping method for a cadmium telluride thin film solar cell, which specifically includes the following steps:

[0085] (1) Prepare a 10 mg / L mixed aqueous solution of SbF3 and BiF3 as follows:

[0086] (1.1) Using clean weighing paper and an analytical balance, weigh 0.5 mg of SbF3 and 0.5 mg of BiF3 into a clean plastic beaker;

[0087] (1.2) Use a clean plastic measuring cylinder to weigh 50 mL of ultrapure water and pour it into the plastic beaker containing SbF3 and BiF3 in (1.1);

[0088] (1.3) Use a plastic rod to stir the solution thoroughly to completely dissolve SbF3 and BiF3;

[0089] (1.4) Pour the solution obtained in (1.3) into a 100 mL plastic volumetric flask;

[0090] (1.5) Use a small amount of ultrapure water in the plastic beaker (1.2) to rinse the plastic rod (1.3) and the inner wall of the plastic beaker. Pour the rinsed solution into the plastic volumetric flask (1.4). Repeat the above steps 3 times.

[0091] (1.6) Use a measuring cylinder and a pipette to add ultrapure water to the plastic volumetric flask in (1.5) and make up to 100 mL.

[0092] (2) Spraying a wet film on one side of the cadmium telluride absorption layer, specifically:

[0093] (2.1) Place the atomization equipment (Fulin-W001) and the sealed atomization chamber in a fume hood;

[0094] (2.2) Open the mist chamber, place the CdTe film sample in the center and then close the mist chamber;

[0095] (2.3) Add a sufficient amount of the 10 mg / L mixed aqueous solution of SbF3 and BiF3 obtained in (1) into the atomizing device;

[0096] (2.4) Turn on the atomization equipment and generate sufficient mist with a droplet size of 4.1 mm in the mist chamber at a rate of 3.3 mL / min;

[0097] (2.5) Keep the CdTe film sample in the mist for 5 minutes.

[0098] (3) Drying treatment, specifically:

[0099] The sprayed sample was transferred to a heating table at 80°C and heated for 10 min to fully dry.

[0100] (4) High temperature annealing, specifically:

[0101] (4.1) Raise the temperature of the tubular annealing furnace to 420°C;

[0102] (4.2) Introduce dry air into the tube furnace;

[0103] (4.3) After 10 minutes, place the dried sample in a graphite boat and push it into the center of the tube furnace;

[0104] (4.4) After 20 min, take the sample out of the tube furnace and allow it to cool naturally to room temperature in a dry air atmosphere.

[0105] (5) Post-processing, specifically:

[0106] The surface of the annealed sample was rinsed with sufficient ultrapure water to remove residual SbF3 and BiF3, and then fully dried with dry nitrogen.

[0107] Example 3

[0108] This embodiment provides a high-temperature doping method for cadmium telluride thin-film solar cells. Except for replacing the SbF3 aqueous solution with a BiF3 aqueous solution of equal concentration, the remaining steps and conditions are the same as those in Example 1, so they are not described in detail here.

[0109] Example 4

[0110] This embodiment provides a high-temperature doping method for cadmium telluride thin-film solar cells. Except for replacing the SbF3 aqueous solution with an AsF3 aqueous solution of equal concentration, the remaining steps and conditions are the same as those in Embodiment 1, and thus are not described in detail here.

[0111] Example 5

[0112] This embodiment provides a high-temperature doping method for cadmium telluride thin-film solar cells. Except for replacing the mixed aqueous solution of SbF3 and BiF3 with a mixed aqueous solution of SbF3 and AsF3 of equal concentrations, the remaining steps and conditions are the same as those in Example 2, so they are not described here in detail.

[0113] Example 6

[0114] This embodiment provides a high-temperature doping method for cadmium telluride thin-film solar cells. Except for replacing the mixed aqueous solution of SbF3 and BiF3 with a mixed aqueous solution of BiF3 and AsF3 of equal concentrations, the remaining steps and conditions are the same as those in Example 2 and are not described in detail here.

[0115] Example 7

[0116] This embodiment provides a high-temperature doping method for cadmium telluride thin-film solar cells. Except for changing the concentration of the SbF3 aqueous solution to 1 mg / L and adaptively extending the retention time of the CdTe thin film sample in the mist in step (2.5) to 50 min, the remaining steps and conditions are the same as those in Example 1 and are not described in detail here.

[0117] Example 8

[0118] This embodiment provides a high-temperature doping method for cadmium telluride thin-film solar cells. Except for changing the concentration of the SbF3 aqueous solution to 1000 mg / L and adaptively shortening the retention time of the CdTe thin film sample in the mist in step (2.5) to 0.05 min, the remaining steps and conditions are the same as those in Example 1 and are not described in detail here.

[0119] Example 9

[0120] This embodiment provides a high-temperature doping method for cadmium telluride thin-film solar cells. Except for changing the solvent in the SbF3 aqueous solution from ultrapure water to methanol, the remaining steps and conditions are the same as those in Example 1, so they are not described here in detail.

[0121] Example 10

[0122] This embodiment provides a high-temperature doping method for cadmium telluride thin-film solar cells. Except for changing the solvent in the SbF3 aqueous solution from ultrapure water to ethanol, the remaining steps and conditions are the same as those in Example 1, so they are not described in detail here.

[0123] Embodiment 11

[0124] This embodiment provides a high-temperature doping method for a cadmium telluride thin-film solar cell. Except for changing the solvent in the SbF3 aqueous solution from ultrapure water to propanol, the remaining steps and conditions are the same as those in Embodiment 1, and thus will not be described in detail here.

[0125] Example 12

[0126] This embodiment provides a high temperature doping method for a cadmium telluride thin film solar cell. Except that the high temperature annealing temperature is changed to 200° C. and the high temperature annealing time is adaptively changed to 60 minutes, the remaining steps and conditions are the same as those in Embodiment 1, and thus will not be described in detail here.

[0127] Embodiment 13

[0128] This embodiment provides a high temperature doping method for a cadmium telluride thin film solar cell. Except that the high temperature annealing temperature is changed to 500° C. and the high temperature annealing time is adaptively changed to 10 minutes, the remaining steps and conditions are the same as those in Embodiment 1, and thus will not be described in detail here.

[0129] Embodiment 14

[0130] This embodiment provides a high temperature doping method for a cadmium telluride thin film solar cell. Except that the high temperature annealing method is changed to laser annealing, the other steps and conditions are the same as those in Embodiment 1, so they are not described in detail here.

[0131] In this embodiment, the specific steps of the laser annealing are as follows:

[0132] (1) Place the sample to be heated with the film facing upward on a high-temperature resistant ceramic sample table;

[0133] (2) Turn on the laser, adjust the laser wavelength to 800nm, and the total laser power to 10mW;

[0134] (3) Use a beam expander to expand the laser into a 1 cm × 5 cm surface light source;

[0135] (4) Close the protective cover and open the negative pressure system to allow for exhaust;

[0136] (5) Gradually increase the laser power so that the surface source power density reaches 5W / cm 2 ;

[0137] (6) Open the sample baffle and use laser to heat the sample for 10 minutes;

[0138] (7) After heating is completed, turn off the laser and baffle, and allow the sample to cool to room temperature naturally in the air.

[0139] Embodiment 15

[0140] This embodiment provides a high temperature doping method for a cadmium telluride thin film solar cell. Except that the high temperature annealing method is changed to flash annealing, the other steps and conditions are the same as those in Embodiment 1, and thus will not be described in detail here.

[0141] In this embodiment, the specific steps of the flash annealing are as follows:

[0142] (1) Place the sample to be heated with the film facing upward into the annealing system;

[0143] (2) Close the protective cover and open the negative pressure system to allow for exhaust;

[0144] (3) Adjust the flash power to 60J / cm 2 ;

[0145] (4) Start the heating program, heat the sample to 600 °C in 1 min, then stop heating;

[0146] (5) After heating, the sample is cooled naturally to room temperature in air.

[0147] Example 16

[0148] This embodiment provides a high temperature doping method for a cadmium telluride thin film solar cell. Except that the wet film coating method is changed to spin coating, the other steps and conditions are the same as those in Embodiment 1, so they are not described in detail here.

[0149] In this embodiment, the specific steps of spin coating are as follows:

[0150] (1) Place the sample film face up on the sample stage of the spin coater;

[0151] (2) Turn on the vacuum pump and use negative pressure to tightly adsorb the sample on the sample table;

[0152] (3) Use a pipette to add 1 mL of SbF3 solution to the center of the sample.

[0153] (4) Slowly increase the rotation speed to 100 rpm to evenly disperse the solution on the sample surface;

[0154] (5) After the solution is evenly dispersed, increase the speed to 500 rpm, continue for 1 min, and then stop rotating;

[0155] (6) Transfer the wet film after spin coating to a heating table at 150 °C and heat for 5 min to evaporate the solvent;

[0156] (7) After heating, the sample was cooled naturally to room temperature in air.

[0157] Embodiment 17

[0158] This embodiment provides a high temperature doping method for a cadmium telluride thin film solar cell. Except that the wet film coating method is changed to scraping coating, the other steps and conditions are the same as those in Embodiment 1, so they are not described in detail here.

[0159] In this embodiment, the specific steps of scraping are as follows:

[0160] (1) Place the sample film facing upward on the scraping platform;

[0161] (2) Turn on the vacuum pump and use negative pressure to tightly adsorb the sample onto the coating platform;

[0162] (3) Use a pipette to evenly and linearly distribute 1 mL of SbF3 solution on one end of the sample;

[0163] (4) Hold the scraping rod and slowly and evenly scrape the SbF3 solution onto the sample surface;

[0164] (5) Transfer the wet film after scraping to a heating table at 150 °C and heat for 5 min to evaporate the solvent;

[0165] (6) After heating, the sample is cooled naturally to room temperature in air.

[0166] Comparative Example 1

[0167] This comparative example provides a high-temperature doping method for a cadmium telluride thin-film solar cell. Except that the high-temperature annealing temperature is changed to 150° C. and the high-temperature annealing time is adaptively changed to 80 min, the remaining steps and conditions are the same as those in Example 1, so they are not described in detail here.

[0168] Comparative Example 2

[0169] This comparative example provides a high-temperature doping method for cadmium telluride thin-film solar cells. Except for replacing the SbF3 aqueous solution with an SbCl3 aqueous solution of equal concentration, the remaining steps and conditions are the same as those in Example 1, so they are not described in detail here.

[0170] Comparative Example 3

[0171] This comparative example provides a high-temperature doping method for cadmium telluride thin-film solar cells. Except for replacing the SbF3 aqueous solution with a BiCl3 aqueous solution of equal concentration, the remaining steps and conditions are the same as those in Example 1, so they are not described here in detail.

[0172] Comparative Example 4

[0173] This comparative example provides a high-temperature doping method for a cadmium telluride thin-film solar cell. Except for replacing the SbF3 aqueous solution with an AsCl3 aqueous solution of equal concentration, the remaining steps and conditions are the same as those in Example 1, and thus are not described in detail here.

[0174] Performance Testing

[0175] The high temperature doping methods provided in Examples 1-17 and Comparative Examples 1-4 were used to prepare cadmium telluride thin film solar cells, such as Figure 1 As shown, the cadmium telluride thin film solar cell includes a stacked glass substrate 101, a transparent conductive oxide layer 102 (SnO2:F), a window layer 103 (CdS), an absorption layer 104 (CdTe), a back contact layer 105 (ZnTe:Cu) and a back electrode layer 106 (Mo).

[0176] Specifically, the thickness of the glass substrate 101 is 3.2 mm, the thickness of the transparent conductive oxide layer 102 is 400 nm, the thickness of the window layer 103 is 100 nm, the thickness of the absorption layer 104 is 4 mm, the thickness of the back contact layer 105 is 50 nm, and the thickness of the back electrode layer 106 is 200 nm.

[0177] In addition, the glass substrate 101 is ultra-white float glass, the transparent conductive oxide layer 102 is made by chemical vapor deposition technology, the window layer 103 and the absorption layer 104 are both made by close-space sublimation, and the back contact layer 105 and the back electrode layer 106 are both made by sputtering.

[0178] Since the specific preparation process of the above-mentioned layers has no obvious effect on the performance of the final product, the specific steps and parameter conditions of each process are not described here.

[0179] After testing, the carrier concentration, minority carrier lifetime and open circuit voltage of the cadmium telluride thin film solar cells obtained by the high temperature doping methods provided in Examples 1-17 and Comparative Examples 1-4 are shown in Table 1 below.

[0180] Table 1 Carrier concentration, minority carrier lifetime and open circuit voltage of cadmium telluride thin film solar cells obtained by the high temperature doping method provided in Examples 1-17 and Comparative Examples 1-4

[0181]

[0182] In Table 1 above, the detection of carrier concentration is based on the capacitance-voltage test (CV) of the sudden pn junction; the detection of minority carrier lifetime refers to the time-resolved photoluminescence (TRPL) standard; and the detection of open circuit voltage refers to IEC 60904-1 for simulated sunlight test.

[0183] It can be seen that the present invention uses fluorides of group V elements to perform high-temperature doping on the cadmium telluride absorption layer. Since the fluorides of group V elements have a relatively high melting point, they can be subjected to high-temperature annealing at a temperature above 200° C., thereby increasing the activation ratio of group V elements and making up for the defect of insufficient annealing of chlorides of group V elements used in the conventional method. The effective doping concentration is increased while taking into account the lifetime of photogenerated carriers, thereby ultimately increasing the open circuit voltage and photoelectric conversion efficiency of the cadmium telluride thin-film solar cell, which is conducive to large-scale promotion and application.

[0184] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A high temperature doping method for a cadmium telluride thin film solar cell, comprising: A wet film containing a doping substance is coated on one surface of a cadmium telluride absorption layer, and a non-in-situ doped cadmium telluride absorption layer is obtained after high-temperature annealing, wherein the doping substance includes a fluoride of a group V element, and the temperature of the high-temperature annealing is ≥200°C.

2. The high temperature doping method according to claim 1, characterized in that: The group V element fluoride includes any one of SbF3, BiF3 or AsF3, or a combination of at least two of them.

3. The high temperature doping method according to claim 2, characterized in that: The group V element fluoride is a combination of at least two of SbF3, BiF3 or AsF3.

4. The high temperature doping method according to claim 2 or 3, characterized in that: The concentration of the group V element fluoride in the wet film is 1-1000 mg / L; and / or, the solvent in the wet film includes water or an organic solvent; And / or, the organic solvent includes any one of methanol, ethanol or propanol, or a combination of at least two of them.

5. The high temperature doping method according to claim 1, characterized in that: The high temperature annealing temperature is 200-600°C; And / or, the high temperature annealing time is 1-60 min.

6. The high temperature doping method according to claim 1, characterized in that: The high temperature annealing method includes any one of furnace annealing, laser annealing or flash annealing; And / or, the high temperature annealing is performed in an atmosphere of air or protective gas; And / or, the protective gas includes nitrogen and / or an inert gas.

7. The high temperature doping method according to claim 1, characterized in that: The wet film coating method includes any one of spray coating, spin coating or blade coating; And / or, the wet film is dried before high-temperature annealing.

8. The high temperature doping method according to claim 1, characterized in that: The cadmium telluride absorption layer is sequentially cooled, cleaned and dried after high temperature annealing; And / or, the cooling includes natural cooling in an atmosphere of air or protective gas.

9. A cadmium telluride thin film solar cell comprising a stacked glass substrate, a transparent conductive oxide layer, a window layer, an absorption layer, a back contact layer and a back electrode layer, characterized in that: The absorption layer is non-in-situ doped with fluoride of group V elements by the high-temperature doping method as described in any one of claims 1 to 8.

10. The cadmium telluride thin film solar cell according to claim 9, characterized in that: The carrier concentration of the cadmium telluride thin film solar cell is ≥5×10 15 cm -3 , minority carrier lifetime ≥ 20ns, open circuit voltage ≥ 850mV.

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