CN112531078B - Defect passivation method for solving problem of light attenuation of copper indium gallium selenide solar cell - Google Patents

Abstract

The invention discloses a defect passivation method for solving the problem of light decay of a copper indium gallium selenide solar cell, comprising the following steps: (1) depositing a Mo back electrode on a substrate; (2) depositing a copper indium gallium on the Mo back electrode selenium light absorption layer; (3) depositing a CdS buffer layer on the copper indium gallium selenide light absorption layer; (4) depositing a high resistance i-ZnO layer and a ZnO:Al window layer on the CdS buffer layer to form a copper indium gallium selenide solar energy (5) Defect passivation treatment for copper indium gallium selenide solar cells. The invention can effectively reduce the defect density of the copper indium gallium selenide solar cell, prolong the optimal service life of the copper indium gallium selenide thin film solar cell, and improve the actual use power of the outdoor copper indium gallium selenide thin film solar cell.

Description

A defect passivation method to solve the problem of light decay of copper indium gallium selenide solar cells

technical field

The invention relates to the technical field of solar cell production, in particular to a defect passivation method for solving the problem of light decay of copper indium gallium selenide solar cells.

Background technique

With the increasingly serious energy crisis, people pay more and more attention to renewable energy. Among them, solar energy has become the most potential technology with its inexhaustible, clean and pollution-free technology, and silicon-based solar energy technology is currently the most mature technology. , also has the highest market share, but it is not the most ideal solar technology due to the high energy consumption and high pollution preparation process. In recent years, thin film solar technology has begun to rise. , easy installation and other advantages, once it was proposed, it has developed rapidly. Among them, copper indium gallium selenide thin film solar cells have many advantages such as high photoelectric conversion efficiency, good stability, radiation resistance, etc., and have become the most promising thin film photovoltaics. device.

The basic structure of a copper indium gallium selenide solar cell consists of a substrate, a back electrode layer, an absorption layer, a buffer layer, a window layer, an antireflection layer, and an electrode layer. In theory, the light decay of CIGS solar cells is much weaker than that of crystalline silicon solar cells and amorphous silicon solar cells, but in actual use, CIGS solar cells have different degrees of light decay. This may be caused by the following reasons:

1. For CIGS cells, cells with high alkali metal content are prone to light decay. This is due to the excessive sodium doping during the preparation of the absorption layer, which leads to the excitation of sodium from the absorption layer. The migration of the boundary site to the depletion layer, the accumulation of sodium in the depletion layer and the transport through the depletion layer cause the reduction of the internal electric field, this migration causes the generation of shunt paths, and the generation of shunt paths leads to parallel resistance and open circuit The drop in voltage causes the phenomenon of light decay. Theelen, M., Hans, V., Barreau, N., Steijvers, H., Vroon, Z., & Zeman, M.(2015). The impact of alkali elements on the degradation of CIGS solar cells.Progress in Photovoltaics : Research and Applications, 23(5), 537–545. doi:10.1002/pip.2610.

2. Under the long-term outdoor use, the AZO layer will appear hydration under the action of light excitation and water vapor, and a part of ZnO will gradually form Zn(OH) ₂ , which will lead to the decline of the electrical performance of the cell and the phenomenon of light decay. Han, C. (2020). Analysis of moisture-induced degradation of thin-film photovoltaic module. Solar Energy Materials and Solar Cells, 210, 110488. doi:10.1016/j.solmat.2020.110488.

3. During the preparation process of the absorber layer, the Mo layer of the back electrode will form a MoSe ₂ layer with Se. If the MoSe ₂ layer is too thin, the Mo layer will be easily oxidized under the action of water vapor and temperature to form MoO during the use of the CIGS battery. At the same time, Na ⁺ enters into MoO _x matrix and oxygen reduction reaction occurs _{: , Different sodium content in Na x MoO 3} leads to different electrical conductivity and makes Na ⁺ diffuse into the film layer, which leads to the generation of light in CIGS cells decline. Theelen, M., & Daume, F. (2016). Stability of Cu(In,Ga)Se ₂ solar cells: A literature review. Solar Energy, 133, 586–627. doi:10.1016/j.solener.2016.04. 010.

Under the existing process preparation method, copper indium gallium selenide thin-film solar cells are prone to light decay during actual outdoor use. The normal use power and expected service life of copper indium gallium selenide thin film solar cells.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a defect passivation method for solving the problem of light decay of copper indium gallium selenide solar cells, which can effectively reduce the defect density of copper indium gallium selenide solar cells and prolong the optimal service life of copper indium gallium selenide thin film solar cells , to improve the actual power of outdoor copper indium gallium selenide thin film solar cells.

The technical scheme adopted by the present invention to solve its technical problems is:

A defect passivation method for solving the problem of light decay of copper indium gallium selenide solar cells, comprising the following steps:

(1) Deposition of Mo back electrode on the substrate;

(2) depositing a copper indium gallium selenide light absorbing layer on the Mo back electrode;

(3) depositing a CdS buffer layer on the copper indium gallium selenide light absorption layer;

(4) Depositing a high-resistance i-ZnO layer and a ZnO:Al window layer on the CdS buffer layer to form a copper indium gallium selenide solar cell;

(5) Defect passivation treatment for copper indium gallium selenide solar cells, specifically:

Put the copper indium gallium selenide solar cell into the atmosphere furnace, and exhaust the furnace. After the exhaust is completed, the reaction gas is introduced, and the following procedures are used for heat treatment:

Raise the temperature to 80-120°C at a heating rate of 5-10°C per minute, keep the temperature for 1-3 hours, and use type I reactive gas;

Raise the temperature to 180-230°C at a heating rate of 2-5°C per minute, keep the temperature for 24-72 hours, and use type II reactive gas;

After the heat treatment is completed, the heating is stopped, the temperature is naturally lowered to room temperature, the furnace is pumped and compressed air is introduced to obtain a copper indium gallium selenide solar cell after the heat treatment.

Preferably, the thickness of the Mo back electrode is 450-550 nm.

Preferably, the thickness of the copper indium gallium selenide light absorbing layer is 1.0-3.0 μm.

Preferably, the thickness of the CdS buffer layer is 30-70 nm.

Preferably, the total thickness of the i-ZnO layer and the ZnO:Al window layer is controlled at 110-250 nm.

Preferably, in step (5), the flow rate of the reaction gas is controlled at 10 - 50 cm ³ ·min ^-1 .

Preferably, the I-type reaction gas is an inert gas, and the inert gas is selected from nitrogen, argon, and nitrogen/argon mixture. The volume content of nitrogen in the nitrogen/argon mixture is 10-90%.

Preferably, the type II reactive gas is an oxidizing gas, and the oxidizing gas is selected from one of dry air and an oxygen/argon mixture. The volume content of oxygen in the oxygen/argon mixture is 20-70%.

Preferably, in step (2), an alkali metal preset layer is first deposited on the Mo back electrode, and then a copper indium gallium selenide light absorbing layer is deposited. The thickness of the alkali metal preset layer is 2-20 nm, and the material of the alkali metal preset layer is selected One of NaF, KF, RbF, CsF.

Preferably, the copper indium gallium selenide light absorbing layer is deposited by a three-step co-evaporation method. The first step: raising the substrate temperature to 300-450 ° C, co-evaporating In, Ga, and Se, the deposition thickness is 0.5-1.2 μm, wherein 0.2≤Ga/(In+Ga)≤0.5; the second step: raise the substrate temperature to 450-650℃, co-evaporate Cu and Se, and the deposition thickness is 0.5-0.8μm, so that 0.95≤Cu/(In+ Ga)≤1.20; Step 3: Keep the substrate temperature unchanged, co-evaporate In, Ga, Se, the deposition thickness is 0.2-0.5μm, and finally control CIGS 0.82≤Cu/(In+Ga)≤0.95, 0.2≤ Ga/(In+Ga)≤0.4.

The beneficial effects of the present invention are:

The heat treatment performed after the preparation of the copper indium gallium selenide window layer in the present invention can effectively reduce the defect density inside the copper indium gallium selenide solar cell and increase the stability of the copper indium gallium selenide solar cell during use.

The defect passivation technology of the present invention can reduce the surface resistance of the thin film, increase the electrical conductivity of the thin film, and enhance its optoelectronic properties.

The defect passivation technology of the invention can effectively reduce the light decay phenomenon of the copper indium gallium selenide solar cell in the screen printing process after being used outdoors for a long time, and increase the actual use power and the expected service life of the copper indium gallium selenide solar cell.

Since the copper screen printing process is different from the screen printing process, there is no silver paste sintering step in the production process, which leads to more obvious light decay phenomenon of the copper screen printing cell during use. The defect passivation technology of the present invention not only improves the copper screen printing process. The photoelectric conversion efficiency of the cell under the screen imprinting process is increased by about 0.2%, and the light decay phenomenon during its use is effectively suppressed.

Description of drawings

Figure 1 shows the defect density diagram of the copper indium gallium selenide cell after heat treatment and without heat treatment.

Figure 2 is a partial view of the square resistance of the window layer after heat treatment and without heat treatment.

Figure 3 shows the light decay curves of the cells tested without heat treatment and after heat treatment under the copper mesh embossing process.

Figure 4 shows the light decay curves of the cells tested without heat treatment and after heat treatment under the screen printing process.

Detailed ways

The technical solutions of the present invention will be further described in detail below through specific embodiments.

In the present invention, unless otherwise specified, the raw materials and equipment used can be purchased from the market or commonly used in the field. The methods in the following examples, unless otherwise specified, are conventional methods in the art.

general implementation

A defect passivation method for solving the problem of light decay of copper indium gallium selenide solar cells, comprising the following steps:

(1) Deposit Mo back electrode on the substrate; the thickness of Mo back electrode is 450-550nm.

(2) First deposit an alkali metal pre-layer on the Mo back electrode, and then deposit a copper indium gallium selenide light absorbing layer. The thickness of the alkali metal pre-layer is 2-20nm, and the material of the alkali metal pre-layer is selected from NaF, KF, RbF , one of CsF. The thickness of the copper indium gallium selenide light absorption layer is 1.0-3.0 μm. The copper indium gallium selenide light absorption layer is deposited by a three-step co-evaporation method. The first step: the substrate temperature is raised to 300-450 ° C, and In, Ga and Se are co-evaporated, and the deposition thickness is 0.5-1.2 μm, where 0.2≤Ga /(In+Ga)≤0.5; the second step: raise the substrate temperature to 450-650℃, co-evaporate Cu and Se, the deposition thickness is 0.5-0.8μm, so that 0.95≤Cu/(In+Ga)≤ 1.20; Step 3: Keep the substrate temperature unchanged, co-evaporate In, Ga, Se, the deposition thickness is 0.2-0.5μm, and finally control 0.82≤Cu/(In+Ga)≤0.95 in CIGS, 0.2≤Ga/( In+Ga)≤0.4.

(3) depositing a CdS buffer layer on the copper indium gallium selenide light absorbing layer; the thickness of the CdS buffer layer is 30-70 nm.

(4) A high-resistance i-ZnO layer and a ZnO:Al window layer were deposited on the CdS buffer layer to form a copper indium gallium selenide solar cell; the total thickness of the i-ZnO layer and the ZnO:Al window layer was controlled at 110-250 nm.

(5) Defect passivation treatment for copper indium gallium selenide solar cells, specifically:

Put the copper indium ^{gallium selenide} solar cell into the atmosphere furnace, and the furnace chamber is pumped. After the pumping is completed, the reaction gas is introduced.

The temperature is raised to 80-120°C at a heating rate of 5-10°C per minute, and the temperature is maintained for 1-3 hours. The I-type reaction gas is used; the I-type reaction gas is an inert gas, and the inert gas is selected from nitrogen, argon, and nitrogen/argon mixed. A kind of air.

The temperature is increased to 180-230°C at a heating rate of 2-5°C per minute, and the temperature is maintained for 24-72 hours, and a type II reaction gas is used; the type II reaction gas is an oxidizing gas, and the oxidizing gas is selected from dry air, oxygen/ One of the argon mixtures.

After the heat treatment is completed, the heating is stopped, the temperature is naturally lowered to room temperature, the furnace is pumped and compressed air is introduced to obtain a copper indium gallium selenide solar cell after the heat treatment.

Example 1

1. A layer of Mo back electrode with a thickness of 500 nm was covered on the stainless steel substrate by magnetron sputtering.

2. Raise the substrate temperature to 300°C in a co-evaporation chamber with a vacuum of 1×10 ^-3 Pa, and co-evaporate a NaF layer on the surface of the Mo layer. The NaF evaporation source temperature is 765°C and the evaporation time is 10min. .

The first step deposition: raise the substrate temperature to 550°C, co-evaporate In, Ga, and Se, where the In evaporation source temperature is 1040°C, the Ga evaporation source temperature is 1120°C, the Se evaporation source temperature is 460°C, and the evaporation time is 10min.

The second step of deposition: keep the substrate temperature unchanged, and evaporate Cu and Se, wherein the Cu evaporation source temperature is 1350°C, the Se evaporation source temperature is 480°C, and the evaporation time is 20min.

The third step deposition: keep the substrate temperature unchanged, co-evaporate In, Ga, and Se, where the In evaporation source temperature is 1010 °C, the Ga evaporation source temperature is 1080 °C, the Se evaporation source temperature is 440 °C, and the evaporation time is 10min.

3. A CdS buffer layer with a thickness of 45 nm was deposited on the copper indium gallium selenide thin film layer by chemical water bath method.

4. A high-resistance i-ZnO layer and a ZnO:Al window layer with a total thickness of 120 nm were deposited on the copper indium gallium selenide thin film layer by magnetron sputtering.

5. Put the copper indium gallium selenide solar cell into the atmosphere furnace, pump the furnace chamber, flush nitrogen into the furnace chamber at a speed of 20cm ³ ·min ^-1 , and heat the atmosphere furnace at a speed of 5°C ·min ^-1 to 100°C, and kept for 2 hours; then, the furnace was evacuated and dry air was introduced, and the atmosphere furnace was heated to 200°C at a speed of 2°C·min ^-1 , and kept for 48 hours.

6. Stop the heating of the atmosphere furnace, and after the atmosphere furnace is cooled to room temperature, the nitrogen in the furnace is drawn out and compressed air is introduced, and the copper indium gallium selenide solar cell after the heat treatment is obtained after the furnace is opened.

7. Using the copper mesh embossing process and lamination process under the same conditions for the heat-treated copper indium gallium selenide solar cell and the unheated copper indium gallium selenide solar cell to obtain a finished copper indium gallium selenide solar cell.

8. Put the two kinds of copper indium gallium selenide solar cells in the outdoor for 60 days of actual use, keep the module temperature at 25 ℃, use a B-level simulator that meets the requirements of IEC 904-9, according to the provisions of GB/T 6495.1, at 1000W· Under the irradiance of m ^-2 , the current-voltage characteristics of the cell were measured every 10 days, and the light decay curve of the cell was obtained after processing the data. Figure 3 shows that the photoelectric conversion efficiency of the copper screen printing process cell after heat treatment is improved, and its light decay effect is significantly weakened.

Example 2

1. A layer of Mo back electrode with a thickness of 500nm was covered on the stainless steel substrate by magnetron sputtering;

2. Raise the substrate temperature to 280 °C in a co-evaporation chamber with a vacuum of 1×10 ^-3 Pa, and co-evaporate a NaF layer on the surface of the Mo layer. The NaF evaporation source temperature is 770 °C and the evaporation time is 10 min. .

The first step deposition: raise the substrate temperature to 525°C, co-evaporate In, Ga, and Se, where the In evaporation source temperature is 1060°C, the Ga evaporation source temperature is 1130°C, the Se evaporation source temperature is 465°C, and the evaporation time is 10min.

The second deposition step: keep the substrate temperature unchanged, and evaporate Cu and Se, wherein the Cu evaporation source temperature is 1380°C, the Se evaporation source temperature is 480°C, and the evaporation time is 19min.

The third step deposition: keep the substrate temperature unchanged, co-evaporate In, Ga, and Se, where the In evaporation source temperature is 995 °C, the Ga evaporation source temperature is 1040 °C, the Se evaporation source temperature is 450 °C, and the evaporation time is 15min.

3. A 50nm thick CdS buffer layer was deposited on the copper indium gallium selenide thin film layer by chemical water bath method;

4. A high-resistance i-ZnO layer and a ZnO:Al window layer with a total thickness of 110 nm were deposited on the copper indium gallium selenide thin film layer by magnetron sputtering.

5. Put the copper indium gallium selenide solar cell into the atmosphere furnace, pump the furnace chamber, and rush into the furnace chamber with a nitrogen/argon gas mixture with a volume ratio of 9:1 at a speed of 30 cm ³ ·min ⁻¹ . The atmosphere furnace was heated to 90°C at a speed of 10°C·min ^-1 , and kept for 3 hours; then the furnace was evacuated, and an oxygen/argon mixture with a volume ratio of 3:7 was introduced, and the temperature was 5°C·min ^-1 . Speed the atmosphere furnace to 180°C and hold for 72 hours.

6. Stop the heating of the atmosphere furnace. After the atmosphere furnace is cooled to room temperature, the nitrogen/argon gas mixture in the furnace is drawn out and compressed air is introduced. After the furnace is opened, the heat-treated copper indium gallium selenide solar cell is obtained.

7. Using the screen printing process and lamination process under the same conditions for the heat-treated copper indium gallium selenide solar cell and the unheated copper indium gallium selenide solar cell to obtain a finished copper indium gallium selenide solar cell.

8. Put the two kinds of copper indium gallium selenide solar cells in the outdoor for 60 days of actual use, keep the module temperature at 25 ℃, use a B-level simulator that meets the requirements of IEC 904-9, according to the provisions of GB/T 6495.1, at 1000W· Under m ^-2 irradiance, the current-voltage characteristics of the cell were measured every 10 days, and the light decay curve of the cell was obtained after processing the data. Figure 4 shows that the light decay effect of the screen-printed cell after heat treatment is significantly improved.

Figure 1 is the defect density diagram of the copper indium gallium selenide cell (prepared according to the method of Example 1) after heat treatment and without heat treatment. When the defect density inside the CIGS cell is high, the alkali metal elements usually aggregate near the interface, which leads to further segregation of the alkali metal elements during the actual use of the cell, which will cause the charge near the interface and the charge distribution inside the absorber layer. Non-uniformity, the photoelectric performance of the cell is reduced, resulting in the phenomenon of light decay. After the TCO process, the defect density inside the cell decreases after the defect passivation treatment, which can effectively prevent the accumulation of alkali metals at the grain boundary, reduce the segregation phenomenon during use, and reduce the light decay effect. Figure 2 is a partial view of the square resistance of the window layer after heat treatment and without heat treatment. After the TCO process, the surface resistance of the heat-treated cell decreased. This may be due to the fact that the surface of the cell is denser and the porosity is reduced after a long time of heat treatment. Small, the reduction of the square resistance can bring about the improvement of the FF of the cell.

The above-mentioned embodiment is only a preferred solution of the present invention, and does not limit the present invention in any form, and there are other variations and modifications under the premise of not exceeding the technical solution recorded in the claims.

Claims (8)

1. A defect passivation method for solving the problem of light decay of a copper indium gallium selenide solar cell is characterized by comprising the following steps:

(1) depositing a Mo back electrode on a substrate;

(2) depositing a copper indium gallium selenide light absorption layer on the Mo back electrode;

(3) depositing a CdS buffer layer on the CIGS light absorption layer;

(4) depositing a high-resistance i-ZnO layer and ZnO, namely an Al window layer on the CdS buffer layer to form the copper indium gallium selenide solar cell;

(5) the method for passivating the defects of the CIGS solar cell specifically comprises the following steps:

placing the CIGS solar cell into an atmosphere furnace, exhausting air from a hearth, introducing reaction gas after the air is exhausted, and performing heat treatment by adopting the following procedures:

heating to 80-120 deg.C at a rate of 5-10 deg.C per minute, maintaining for 1-3 hr, and using type I reaction gas; the I-type reaction gas is inert gas, and the inert gas is selected from one of nitrogen, argon and nitrogen/argon mixed gas;

raising the temperature to 230 ℃ at the temperature raising speed of 2-5 ℃ per minute, preserving the temperature for 24-72 hours, and adopting II type reaction gas; the II type reaction gas is oxidizing gas, and the oxidizing gas is one of dry air and oxygen/argon mixed gas;

and stopping heating after the heat treatment is finished, naturally cooling to room temperature, exhausting air from the hearth and introducing compressed air to obtain the copper indium gallium selenide solar cell after the heat treatment.

2. The defect passivation method as claimed in claim 1, wherein the thickness of the Mo back electrode is 450-550 nm.

3. The method of claim 1, wherein the CIGS light absorbing layer has a thickness of 1.0-3.0 μm.

4. The defect passivation method of claim 1, wherein the CdS buffer layer has a thickness of 30-70 nm.

5. The defect passivation method as claimed in claim 1, wherein the total thickness of the i-ZnO layer and the ZnO-Al window layer is controlled to be 110-250 nm.

6. The defect passivation method of claim 1, characterized in that, in the step (5), the flow rate of the reaction gas is controlled to be 10-50cm³·min^-1。

7. The defect passivation method of claim 1, wherein in the step (2), an alkali metal pre-deposited layer is deposited on the Mo back electrode, and then the CIGS light absorption layer is deposited, wherein the thickness of the alkali metal pre-deposited layer is 2-20nm, and the material of the alkali metal pre-deposited layer is selected from one of NaF, KF, RbF and CsF.

8. The defect passivation method of claim 1, wherein the CIGS light absorption layer is deposited by a three-step co-evaporation method, wherein the step 1: raising the temperature of the substrate to 300-450 ℃, co-evaporating In, Ga and Se, and depositing the thickness of 0.5-1.2 mu m, wherein Ga/(In + Ga) is more than or equal to 0.2 and less than or equal to 0.5; the second step is that: raising the temperature of the substrate to 650 ℃ of 450 ℃ and co-evaporating Cu and Se, wherein the deposition thickness is 0.5-0.8 mu m, and the Cu/(In + Ga) is more than or equal to 0.95 and less than or equal to 1.20; and 3, step 3: keeping the temperature of the substrate unchanged, co-evaporating In, Ga and Se, wherein the deposition thickness is 0.2-0.5 mu m, and finally controlling Cu/(In + Ga) to be more than or equal to 0.82 and less than or equal to 0.95 and Ga/(In + Ga) to be more than or equal to 0.2 and less than or equal to 0.4 In the CIGS.

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