Manufacturing method of CdTe / CdS photovoltaic cell

Abstract

The invention discloses a method for manufacturing a CdTe / CdS photovoltaic cell, which comprises the following steps of: (1) sequentially depositing a back electrode and a CdTe film on a glass substrate to obtain a substrate / CdTe structure; (2) annealing the substrate / CdTe structure under the annealing conditions that the temperature is raised to 300-400 DEG C at the speed of 90-110 DEG C / min in a 9-11% hydrogen sulfide-nitrogen mixed atmosphere, then the temperature is kept for 5-10 minutes, the flow of the mixed atmosphere is 9-12 sccm, after annealing is finished, the substrate / CdTe structure is naturally cooled to the room temperature, and a CdS film is formed on the CdTe film; the substrate / CdTe / CdS structure with the CdS film is placed in a CdCl2 solution to be soaked, then heat treatment is conducted, and the substrate / CdTe / CdS structure is obtained; and (3) depositing a transparent conductive film on the CdS film to obtain the CdTe / CdS photovoltaic cell. The thickness of the CdS film prepared by the method is stabilized below 100nm, and the prepared heterojunction has photovoltaic response, tight coupling and few interface defects, and is suitable for large-area production.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a photovoltaic device, and particularly to a method for manufacturing a CdTe / CdS photovoltaic cell. Background Art

[0002] CdTe thin-film solar cells have become a research hotspot in the photovoltaic field due to their high light absorption coefficient, low cost, and high efficiency. The CdTe / CdS heterojunction is the core structure of CdTe solar cells, where the CdS thin film, as the window layer, has an important impact on the performance of the cell. The preparation process of traditional CdTe solar cells is to first grow a transparent conductive thin film (TCO) on a glass substrate, then grow a CdS thin film on the TCO by methods such as chemical bath, then grow a CdTe thin film on the CdS thin film by methods such as close-spaced sublimation, and then grow a back contact electrode, forming a CdTe photovoltaic cell with a forward structure of glass / TCO / CdS / CdTe / back electrode. The disadvantages of such cells are that the heterojunction interface coupling between CdS and CdTe is not tight, there are many interface defects resulting in defect recombination carriers, and the transport of photo-generated carriers is limited. In addition, most of the preparation methods of CdS thin films are wet preparation methods, which have problems such as many interface defects and complex processes, and are not suitable for large-area preparation.

[0003] Heterojunctions constructed by in-situ growth technology have received extensive attention because they can form high-quality heterojunction interfaces. The invention patent application with the publication number CN104810249A discloses a method for growing a CdS thin film or CdS nanostructure on a CdTe thin film. This method uses a hydrogen sulfide thermal annealing technique to in-situ form a CdS thin film on the CdTe thin film. However, the CdS nanostructure obtained by this method needs to be established on a micron-scale CdTe thin film, and the thickness of the obtained CdS thin film itself is above 500nm, resulting in the heterojunction being deeply buried in the CdTe matrix, and sunlight cannot reach it, so no photovoltaic effect can be formed. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a method for manufacturing a CdTe / CdS photovoltaic cell to stably adjust the thickness of in-situ generated CdS.

[0005] Technical Solution: The method for manufacturing a CdTe / CdS photovoltaic cell of the present invention includes the following steps:

[0006] (1) Deposit a back electrode and a CdTe thin film on a glass substrate in sequence to obtain a substrate / CdTe structure;

[0007] (2) Anneal the substrate / CdTe structure under the following annealing conditions: in a mixed atmosphere of 9-11% hydrogen sulfide-nitrogen, heat it at a rate of 90-110 °C / min to 300-400 °C, then hold for 5-10 minutes. The flow rate of the mixed atmosphere is 9-12 sccm. After annealing, cool it naturally to room temperature to form a CdS thin film on the CdTe thin film; Place the substrate / CdTe / CdS structure with the CdS thin film in a CdCl 2 solution, soak it, and then perform heat treatment to obtain the substrate / CdTe / CdS structure;

[0008] (3) Deposit a transparent conductive thin film on the CdS thin film to obtain a CdTe / CdS photovoltaic cell.

[0009] Preferably, in step (1), a back electrode is deposited by DC sputtering. The DC sputtering power is 50-150 W, the temperature of the glass substrate is 280-320 °C, and the sputtering time is not less than 1 hour.

[0010] Preferably, in step (1), a transition layer is provided on the back electrode, and the CdTe thin film is deposited on the transition layer. The preparation method of the transition layer is: in a mixed atmosphere of oxygen and argon, heat the glass substrate with the back electrode to 300-400 °C and keep it for more than 30 minutes. The transition layer makes it easy to form an ohmic contact between CdTe and metal Mo.

[0011] Preferably, in step (1), the CdTe thin film is deposited by the close-spaced sublimation method: heat the CdTe powder used to prepare the CdTe thin film to 630-640 °C, and heat the glass substrate deposited with the back electrode to 540-560 °C. When both reach the preset temperature simultaneously, hold for 3-5 minutes to deposit a CdTe thin film on the surface of the back electrode, then cool down. After both are lower than 400 °C simultaneously, cool it naturally to room temperature. Through such parameter control, the thickness of the obtained CdTe thin film is 3-4 microns.

[0012] Preferably, the heating rate of the glass substrate deposited with the back electrode is not less than 12 °C / min, the heating rate of the CdTe powder is greater than that of the glass substrate deposited with the back electrode. After depositing the CdTe thin film, the cooling rate of the glass substrate deposited with the CdTe thin film is not less than 10 °C / min, and the cooling rate of the remaining CdTe powder is greater than that of the glass substrate deposited with the back electrode.

[0013] Preferably, in step (2), the CdCl 2 solution is a saturated aqueous solution of CdCl 2 , and the heat treatment is: heat it at a rate of 3-6 °C / min to above 400 °C and hold for more than 30 minutes.

[0014] Preferably, in step (3), a transparent conductive film is deposited by radio frequency sputtering, with a sputtering power of 50 - 150 W, a temperature of 170 - 220 °C, and a sputtering time of not less than 30 minutes.

[0015] Preferably, in step (1), the work function of the back electrode is higher than that of CdTe, and the thickness is 200 - 400 nm.

[0016] Preferably, in step (1), the back electrode is one of Mo, Au, Pt, Pd, Ni, and CuxTe.

[0017] Preferably, in step (3), the transparent conductive film is an Al-doped ZnO conductive film, and the thickness of the transparent conductive film is 50 - 100 nm.

[0018] Preferably, the method for fabricating a CdTe / CdS photovoltaic cell further includes: leading out electrodes on the back electrode and the transparent conductive film respectively.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: 1. Stably adjusting the thickness of in-situ generated CdS: Through parameter control, the thickness of the obtained CdS film is stably below 100 nm to adapt to the window layer thickness required for CdTe photovoltaic cells; 2. Optimizing the interface characteristics through in-situ sulfurization annealing and CdCl2 treatment to obtain photocurrent and cell efficiency; 3. Using a Mo 2 O 3 transition layer to improve the back electrode contact performance and stability; 4. The CdTe film is rapidly thermally annealed in a hydrogen sulfide atmosphere to in-situ grow a CdS film to form a Cd atom-sharing type heterojunction, with simple process, high-quality heterojunction prepared, low cost, and suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the J-V curve diagram of the CdTe / CdS photovoltaic cell obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] The technical solution of the present invention will be further described below with reference to the drawings.

[0022] Example 1: Obtaining a CdTe / CdS Photovoltaic Cell

[0023] (1) Cleaning of the glass substrate: Cutting a glass sheet of 2 cm * 2 cm * 0.7 mm, successively ultrasonicating with acetone and ethanol for 10 - 20 min; then ultrasonicating with 10% dilute hydrochloric acid for 10 min, ultrasonicating with deionized water for 10 min, and then using N 2 to dry, obtaining the glass substrate.

[0024] (2) Mo thin film: The magnetron sputtering is in the form of DC sputtering mode, the sputtering power is 100 W, the target used is a metal Mo target, the flow rate of argon gas is 10 sccm, the growth gas pressure is 1.5 Pa, the temperature of the glass substrate is 300 °C, the sputtering time is 1 h, and a Mo thin film with a thickness of 200 nm is formed on the glass substrate to obtain a glass / Mo thin film substrate;

[0025] (3) Mo 2 O 3 Intermediate layer and CdTe thin film: The close-spaced sublimation system is evacuated to a vacuum degree ≤ 0.1 Pa, oxygen and argon are respectively introduced, and the gas flow rates are both 20 sccm. The reaction gas pressure is adjusted to 1 Kpa by controlling the valve at the pumping port; the CdTe powder source and the glass / Mo thin film substrate are synchronously heated to 300 °C and maintained for 30 minutes to form a Mo 2 O 3 intermediate layer (the thickness of the intermediate layer is determined by the heating temperature) on the surface of the Mo metal thin film, obtaining a glass / Mo / Mo 2 O 3 structure; the CdTe powder source is heated to 630 °C, and the temperature of the glass / Mo / Mo 2 O 3 substrate is raised to 540 °C (the heating rate > 12 °C / min). After both reach the preset temperature, they are kept warm for 5 minutes. Then the CdTe powder source and the glass / Mo / Mo 2 O 3 substrate are simultaneously cooled to below 400 °C (during cooling, the cooling rate of the glass / Mo / Mo 2 O 3 substrate with the CdTe thin film is not less than 10 °C / min), and then naturally cooled to room temperature. A CdTe thin film with a thickness of 4 μm is formed on the glass / Mo / Mo 2 O 3 structure to obtain a glass / Mo / Mo 2 O 3 / CdTe structure;

[0026] (4) CdS thin film: The glass / Mo / Mo 2 O 3 / CdTe structure is placed in a rapid annealing furnace for sealing. The system is evacuated, and after repeatedly flushing the system with nitrogen 2 - 3 times, a mixed gas of 10 v / v% hydrogen sulfide / nitrogen is introduced, the flow rate is controlled at 10 sccm, the annealing temperature is selected as 400 °C, the heating rate is 100 °C / min, and the holding time is 5 minutes to obtain a glass / Mo / Mo 2 O 3 / CdTe / CdS structure, and the thickness of the CdS thin film is 100 nm.

[0027] (5) For glass / Mo / Mo 2 O 3 / CdTe / CdS structure, perform CdCl 2 atmosphere annealing: Add 0.5 g of CdCl 2 to 50 ml of deionized water to obtain a saturated CdCl 2 solution; Immerse the glass / Mo / Mo 2 O 3 / CdTe / CdS structure in the saturated CdCl 2 solution for 5 s, take it out and air-dry naturally; Place the air-dried glass / Mo / Mo 2 O 3 / CdTe / CdS structure in a tube furnace for annealing, with a heating rate of 5 °C / minute, an annealing temperature of 400 °C, and hold for 30 minutes;

[0028] (6) Preparation of Al-doped ZnO transparent conductive thin film (AZO): The magnetron sputtering form is radio frequency sputtering mode, the sputtering power is 100 W, an Al-doped ZnO target is used, the flow rates of oxygen and argon are both 10 sccm, the growth pressure is 1 Pa, the substrate temperature is 200 °C, and the sputtering time is 30 minutes to obtain a glass / Mo / Mo 2 O 3 / CdTe / CdS / AZO structure, and the thickness of the AZO transparent conductive thin film is 100 nm.

[0029] (7) Lead out electrodes on the back electrode Mo of the glass / Mo / Mo 2 O 3 / CdTe / CdS / AZO structure and lead out electrodes on the AZO to obtain a CdTe photovoltaic cell.

[0030] Under the irradiation of simulated sunlight, the efficiency of the cell was tested. As can be seen from Figure 1 , this in-situ growth method can obtain the cell efficiency, proving that this method for growing CdTe cells is feasible.

[0031] Comparative Example 1: This comparative example is similar to Example 1, except that in step (4), the annealing temperature is 480 °C, and the prepared CdTe / CdS photovoltaic cell has no photovoltaic response.

[0032] Comparative Example 2: This comparative example is similar to Example 1, except that in step (4), the heating rate is 10 °C / minute, and the prepared CdTe / CdS photovoltaic cell has no photovoltaic response.

[0033] Comparative Example 3: This comparative example is similar to Example 1, except that in step (4), the heat preservation time is 50 minutes, and the obtained CdTe / CdS photovoltaic cell has no optoelectronic response.

Claims

1. A method for manufacturing a CdTe / CdS photovoltaic cell, characterized in that: The following steps are involved: (1) depositing a back electrode and a CdTe film on a glass substrate in sequence to obtain a substrate / CdTe structure; (2) annealing the substrate / CdTe structure, the annealing conditions are: in a mixed atmosphere of 9% to 11% hydrogen sulfide-nitrogen, heating to 300-400°C at a rate of 90-110°C / min, holding for 5-10 minutes, and a mixed atmosphere flow rate of 9-12 sccm. After annealing, the film is naturally cooled to room temperature to form a CdS film on the CdTe film; the substrate / CdTe / CdS structure with the CdS film is immersed in a CdCl2 solution, and then subjected to heat treatment to obtain a substrate / CdTe / CdS structure; (3) A transparent conductive film is deposited on the CdS film to obtain a CdTe / CdS photovoltaic cell.

2. The method for manufacturing a CdTe / CdS photovoltaic cell according to claim 1, characterized in that: In step (1), the back electrode is deposited by direct current sputtering, the direct current sputtering power is 50 to 150 W, the glass substrate temperature is 280 to 320° C., and the sputtering time is not less than 1 hour.

3. The method for manufacturing a CdTe / CdS photovoltaic cell according to claim 1, characterized in that: In step (1), a transition layer is provided on the back electrode, and the CdTe film is deposited on the transition layer. The preparation method of the transition layer is: in a mixed atmosphere of oxygen and argon, the glass substrate with the back electrode is heated to 300-400°C and maintained for more than 30 minutes.

4. The method for manufacturing a CdTe / CdS photovoltaic cell according to claim 2 or 3, characterized in that: In step (1), a CdTe thin film is deposited by a close-space sublimation method: the CdTe powder is heated to 630-640°C, and the glass substrate with a back electrode deposited thereon is heated to 540-560°C. Both of them reach a preset temperature at the same time, and are kept warm for 3-5 minutes. The temperature is then lowered until both are below 400°C, and the mixture is naturally cooled to room temperature.

5. The method for manufacturing a CdTe / CdS photovoltaic cell according to claim 4, characterized in that: The heating rate of the glass substrate with the back electrode deposited is not less than 12°C / min, and after the CdTe film is deposited, the cooling rate is not less than 10°C / min.

6. The method for manufacturing a CdTe / CdS photovoltaic cell according to claim 1, characterized in that: In step (2), the CdCl2 solution is a saturated aqueous solution of CdCl2, and the heat treatment is: heating to above 400°C at a rate of 3-6°C / min and keeping the temperature for more than 30 minutes.

7. The method for manufacturing a CdTe / CdS photovoltaic cell according to claim 1, characterized in that: In step (3), the transparent conductive film is deposited by radio frequency sputtering, the sputtering power is 50-150 W, the temperature is 170-220° C., and the sputtering time is not less than 30 minutes.

8. The method for manufacturing a CdTe / CdS photovoltaic cell according to claim 1, characterized in that: In step (1), the work function of the back electrode is higher than that of CdTe, and the thickness is 200 to 400 nm.

9. The method for manufacturing a CdTe / CdS photovoltaic cell according to claim 1, characterized in that: In step (1), the back electrode is one of Mo, Au, Pt, Pd, Ni and CuxTe.

10. The method for manufacturing a CdTe / CdS photovoltaic cell according to claim 1, characterized in that: In step (3), the transparent conductive film is an Al-doped ZnO conductive film, and the thickness of the transparent conductive film is 50 to 100 nm.

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