GaAs / WSe2 heterojunction solar cell and preparation method thereof

Abstract

The invention belongs to the field of semiconductor materials, and discloses a GaAs / WSe2 heterojunction solar cell and a preparation method thereof, and the solar cell comprises a back electrode, a GaAs substrate, a WSe2 hole transport layer and a front electrode. According to the preparation method, a WSe2 thin film is grown by using a direct-current magnetron sputtering and CVD two-step method, then the grown WSe2 thin film is transferred to a processed GaAs substrate with a back electrode through a two-dimensional material wet transfer technology, and finally a front electrode is prepared, so that the GaAs / WSe2 heterojunction solar cell is prepared. The heterojunction of the TMDs material and the GaAs is a structure with a great development prospect in optoelectronic devices. WSe2 is adopted as one end of the TMDs / GaAs heterojunction and can be matched with GaAs to form an excellent II-type energy band structure, the HOMO energy level of the WSe2 is close to that of the GaAs, the LUMO energy level of the WSe2 is higher than that of the GaAs, and selective contact of carriers can be effectively carried out. The WSe2 thin film prepared by the method is large in size, and the heterojunction solar cell is low in cost and high in efficiency.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor materials, and more specifically, to a GaAs / WSe2 heterojunction solar cell and a preparation method thereof, and belongs to the field of GaAs solar cells. Background Art

[0002] In recent years, GaAs (Gallium Arsenide) solar cells have been widely used in the field of aerospace batteries due to their direct band gap, excellent photoelectric conversion efficiency and radiation resistance. According to the Shockley-Queisser model, the photoelectric conversion efficiency of a single-junction GaAs solar cell can reach 30%. Transition metal dichalcogenides (TMDs) materials have been widely studied due to their satisfactory electronic and optoelectronic properties. They have adjustable band gaps and high light absorption coefficients. The 2D / 3D heterojunctions prepared by combining with semiconductors such as Si and GaAs have been shown to have excellent photoelectric properties.

[0003] The preparation of Si / WSe2 heterojunction was reported in the document Photovoltaic activity of WSe2 / Si hetero junction. Materials Research Bulletin (2019). In this document, WSe2 thin film was formed by liquid phase exfoliation of bulk WSe2, and then a heterojunction was formed on the substrate by drop casting and spin coating. The WSe2 thin film formed by this method is prone to agglomeration, and the low concentration makes it difficult to form a thin film. In previous studies, there have been no reports of GaAs / WSe2 heterojunction photovoltaic devices. Summary of the invention

[0004] In order to overcome the above-mentioned problems, the present invention provides a method for preparing a GaAs / WSe2 heterojunction solar cell, in which a WSe2 thin film is grown by a two-step method of magnetron sputtering and CVD, a heterojunction is formed on GaAs by a two-dimensional material wet transfer technology, and finally an upper electrode is evaporated to prepare a GaAs / WSe2 heterojunction solar cell.

[0005] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0006] A GaAs / WSe2 heterojunction solar cell comprises a back electrode, a GaAs substrate, a WSe2 hole transport layer and a front electrode from bottom to top.

[0007] Preferably, the thickness of the WSe2 hole transport layer is 80-150 nm.

[0008] Preferably, the GaAs substrate is an n-type GaAs substrate with a thickness of 250-350 μm and a Si doping concentration of (1-3)×10 18 / cm 3 , the crystal plane is (110) crystal plane.

[0009] Preferably, the back electrode is Au; the thickness of the back electrode is 100-120 nm; the front electrode is one or more of silver, titanium, copper, nickel, platinum, and indium tin oxide; the thickness of the front electrode is 100-120 nm.

[0010] A method for preparing a GaAs / WSe2 heterojunction solar cell comprises the following steps:

[0011] Step 1: Mount the Si wafer with the SiO2 layer on the sample stage of a magnetron sputtering instrument, and use a W metal target to sputter a thin W metal film on the Si wafer with the SiO2 layer;

[0012] Step 2: Place the sample prepared in step 1 into a quartz boat downstream of the CVD, add Se powder into the quartz boat upstream, introduce nitrogen, and grow the WSe2 film at a certain temperature;

[0013] Step 3, spin-coat a layer of PMMA on the sample obtained in step 2 and dry it, then put it into a dilute HF acid solution for etching to peel off the WSe2 film;

[0014] Step 4: evaporate a back electrode layer on the back of n-type GaAs, and after cleaning, transfer the WSe2 film in step 3 to the GaAs substrate by wet method, and then soak it in acetone to remove PMMA and dry it;

[0015] Step 5, using the method of step 4 to deposit a front electrode on the front side of the GaAs / WSe2 heterojunction, a GaAs / WSe2 heterojunction solar cell can be obtained.

[0016] The two-step method of magnetron sputtering and CVD used in the present invention to prepare WSe2 can form a uniform large-sized film, and the formed film can be simply transferred to the surface of the GaAs substrate through wet transfer technology. The heterojunction battery is easy to prepare and has good development prospects in the field of photovoltaic devices.

[0017] Preferably, the purity of the W metal target material in step 1 is 99.999%, the DC sputtering power is 10W to 30W, the sputtering time is 2 to 20s, and the vacuum degree is 0.4 to 0.8Pa.

[0018] Further preferably, in step 1, the DC sputtering power is 15W to 20W, the sputtering time is 8 to 10s, and the vacuum degree is 0.49Pa.

[0019] Preferably, the purity of the Se powder in step 2 is 99.999%, the distance between the Se powder and the Si substrate is 5 to 10 cm, the growth temperature is 550 to 700° C., the flux of N2 is 50 to 100 sccm, and the insulation time is 10 to 30 min.

[0020] Further preferably, in step 2, the distance between Se powder and substrate is 10 cm, the growth temperature is 600-650° C., and the flux of N2 is 80 sccm.

[0021] Preferably, in step 3, the spin coating of PMMA is performed at a rotation speed of 1000-3000 rpm, a time of 15-30 s, a drying temperature of 60-80° C., a concentration of the dilute HF acid solution of 5 wt % to 15 wt %, and an etching time of 10-15 min.

[0022] Preferably, the Au back electrode described in step 4 has a thickness of 100-120 nm and needs to be annealed to form an ohmic contact at a temperature of 300-350°C.

[0023] Preferably, the cleaning solution of GaAs in step 4 is acetone, ethanol, and 10 wt% dilute hydrochloric acid, the soaking time in acetone is 10 to 15 minutes, and the drying temperature is 60 to 80°C.

[0024] Preferably, the front electrode described in step five can be silver, titanium, copper, nickel, platinum, indium tin oxide, etc.

[0025] Preferably, the thickness of the front electrode in step five is 100-120 nm.

[0026] Preferably, the thickness of the n-type GaAs in step 4 is 250-350 μm, and the Si doping concentration is (1-3) x10 18 / cm 3 The crystal plane is (110).

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

[0028] The present invention prepares WSe2 by a two-step method of magnetron sputtering and CVD to form a uniform large-sized film, and the formed film can be simply transferred to the surface of the GaAs substrate by a wet transfer technology. The heterojunction battery is easy to prepare, and the proposed GaAs / WSe2 heterojunction photovoltaic device has good development prospects in the photovoltaic field. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the Raman spectrum of WSe2 grown by the two-step method in Example 1.

[0030] Figure 2SEM image of WSe2 thin film obtained in Example 1.

[0031] Figure 3 This is a structural diagram of a GaAs / WSe2 heterojunction solar cell.

[0032] Figure 4 It is the IV curve test diagram of the solar cell of Example 2 and Comparative Example 1.

[0033] Figure 5 This is the energy band structure diagram of GaAs / WSe2 heterojunction. DETAILED DESCRIPTION

[0034] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0035] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0036] Example 1

[0037] A method for preparing a GaAs / WSe2 heterojunction solar cell comprises the following steps:

[0038] Step 1: Place the Si wafer with the SiO2 layer on the sample stage of the magnetron sputtering instrument, use a 99.999% pure W metal target, a DC sputtering power of 15W, a sputtering time of 10s, and a vacuum degree of 0.49Pa to sputter a W metal film on the substrate;

[0039] Step 2: Place the sample prepared in step 1 into the quartz boat downstream of the CVD, and put Se powder into the quartz boat upstream. The purity of Se powder is 99.999%. The distance between Se powder and Si substrate is 10 cm. The growth temperature is 600 ° C, the flux of N2 is 80 sccm, and the holding time is 20 min. Grow WSe2 thin film, such as Figure 1 The Raman test results of the grown film are shown, which show the appearance of the WSe2 peak. Figure 2 For its SEM morphology;

[0040] Step 3: Spin-coat a layer of PMMA on the sample obtained in step 2 at a speed of 1500 rpm for 30 seconds, place in an oven at 80°C to dry, and then etch with a 10 wt% dilute HF acid solution for 15 minutes to peel off the WSe2 film;

[0041] Step 4: evaporate a layer of Au electrode on the back of n-type GaAs, the thickness of the Au back electrode is 120nm, and then anneal to form an ohmic contact, the annealing temperature is 330℃. After cleaning with acetone, ethanol, and 10wt% dilute hydrochloric acid, transfer the WSe2 film in step 3 to the GaAs substrate by wet method, soak it in acetone solution to remove PMMA, soak it for 15min, and dry it in a 60℃ oven;

[0042] Step 5: Using the GaAs / WSe2 heterojunction obtained in step 4, a layer of Ag electrode is evaporated on the front side, and the electrode thickness is 100nm, so as to obtain a GaAs / WSe2 heterojunction solar cell. The cell structure is as follows: Figure 3 As shown, the IV curve test is performed on it, and the results are as follows Figure 4 shown.

[0043] Example 2

[0044] A method for preparing a GaAs / WSe2 heterojunction solar cell comprises the following steps:

[0045] Step 1: Place the Si wafer with the SiO2 layer on the sample stage of the magnetron sputtering instrument, use a 99.999% pure W metal target, a DC sputtering power of 20W, a sputtering time of 8s, and a vacuum degree of 0.49Pa to sputter a W metal film on the substrate;

[0046] Step 2: Place the sample prepared in step 1 into a quartz boat downstream of the CVD, and load Se powder into the quartz boat upstream. The purity of Se powder is 99.999%, the distance between Se powder and substrate is 10 cm, the growth temperature is 650°C, the flux of N2 is 80 sccm, the holding time is 30 min, and WSe2 thin film is grown;

[0047] Step 3: Spin-coat a layer of PMMA on the sample obtained in step 2 at a speed of 1000 rpm for 30 seconds, place in an oven at 80°C to dry, and then etch with a 10 wt% dilute HF acid solution for 15 minutes to peel off the WSe2 film;

[0048] Step 4: evaporate a layer of Au electrode on the back of n-type GaAs, the thickness of the Au back electrode is 120nm, and then anneal to form an ohmic contact, the annealing temperature is 330℃. After cleaning with acetone, ethanol, and 10wt% dilute hydrochloric acid, transfer the WSe2 film in step 3 to the GaAs substrate by wet method, soak in acetone to remove PMMA, soak for 10min, and dry in a 60℃ oven;

[0049] Step 5: Using the GaAs / WSe2 heterojunction obtained in step 4, evaporate a layer of Ag electrode on the front side with an electrode thickness of 100 nm to obtain a GaAs / WSe2 heterojunction solar cell.

[0050] Comparative Example 1

[0051] Comparative Example 1 is different from Example 1 and Example 2 in that the WSe2 film is prepared in a different manner. Liquid phase exfoliation is used to obtain a dispersion and then spin coating is performed. The specific implementation method is as follows:

[0052] (1) 30 mg of commercially available WSe2 powder with a purity of 99.999% was dissolved in 25 ml of NMP (N-methylpyrrolidone) and ultrasonically dispersed for 8 h.

[0053] (2) The solution obtained above was centrifuged using a high-speed centrifuge at a speed of 4000 rpm for 20 min, and the supernatant was removed using a pipette for later use.

[0054] (3) A layer of Au electrode is evaporated on the back of the n-type GaAs. The thickness of the Au back electrode is 120 nm. Then, annealing is performed to form an ohmic contact. The annealing temperature is 330° C. The GaAs is cleaned with acetone, ethanol, and 10 wt % dilute hydrochloric acid and blown dry with nitrogen.

[0055] (4) Spin coat a layer of the WSe2 dispersion in NMP obtained in step (2) on the GaAs surface using a spin coating method at a rotation speed of 2000 rpm for 30 seconds.

[0056] (5) Annealing at 200° C. in a nitrogen-filled oven for 20 min to ensure complete removal of NMP.

[0057] (6) Using thermal evaporation and with the aid of a mask, a layer of Ag electrode with a thickness of 100 nm was deposited on the front side to produce a GaAs / WSe2 heterojunction solar cell.

[0058] The device parameters of the solar cell prepared in Example 2 and the solar cell prepared in Comparative Example 1 are shown in Table 1. The IV curve of the solar cell in Example 2 is shown in Figure 4 shown.

[0059] Table 1

[0060]

[0061]

[0062] The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solution disclosed in the present invention, technicians in this field can make some substitutions and deformations to some technical features therein according to the disclosed technical content without creative labor, and these substitutions and deformations are all within the protection scope of the present invention.

Claims

1. A GaAs / WSe2 heterojunction solar cell, characterized in that: It includes a back electrode, a GaAs substrate, a WSe2 hole transport layer and a front electrode from bottom to top.

2. A GaAs / WSe2 heterojunction solar cell according to claim 1, characterized in that: The thickness of the WSe2 hole transport layer is 80-150nm.

3. A GaAs / WSe2 heterojunction solar cell according to claim 1, characterized in that: The GaAs substrate is an n-type GaAs substrate with a thickness of 250-350 μm and a Si doping concentration of (1-3)×10 18 / cm 3 , the crystal plane is (110) crystal plane.

4. A GaAs / WSe2 heterojunction solar cell according to claim 1, characterized in that: The back electrode is Au; the thickness of the back electrode is 100-120 nm; the front electrode is one or more of silver, titanium, copper, nickel, platinum, and indium tin oxide; the thickness of the front electrode is 100-120 nm.

5. A method for preparing a GaAs / WSe2 heterojunction solar cell according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Mount the Si wafer with the SiO2 layer on the sample stage of a magnetron sputtering instrument, and use a W metal target to sputter a thin W metal film on the Si wafer with the SiO2 layer; Step 2: Place the sample prepared in step 1 into a quartz boat downstream of the CVD, add Se powder into the quartz boat upstream, introduce nitrogen, and grow the WSe2 film at a certain temperature; Step 3, spin-coat a layer of PMMA on the sample obtained in step 2 and dry it, then put it into a dilute HF acid solution for etching to peel off the WSe2 film; Step 4: evaporate a back electrode layer on the back of n-type GaAs, and after cleaning, transfer the WSe2 film in step 3 to the n-type GaAs substrate by wet method, and then soak it in acetone to remove PMMA and dry it; Step 5, using the front electrode layer evaporated on the front side of the GaAs / WSe2 heterojunction obtained in step 4, a GaAs / WSe2 heterojunction solar cell can be obtained.

6. The method for preparing a GaAs / WSe2 heterojunction solar cell according to claim 5, characterized in that: The purity of the W metal target material in step 1 is 99.999%, the DC sputtering power is 10W to 30W, the sputtering time is 2 to 20s, and the vacuum degree is 0.4 to 0.8Pa.

7. The method for preparing a GaAs / WSe2 heterojunction solar cell according to claim 5, characterized in that: The purity of the Se powder described in step 2 is 99.999%, the distance between the Se powder and the Si substrate is 5 to 10 cm, the growth temperature is 550 to 700° C., the flux of N2 is 50 to 100 sccm, and the insulation time is 10 to 30 min.

8. The method for preparing a GaAs / WSe2 heterojunction solar cell according to claim 5, characterized in that: In step 3, PMMA is spin-coated at a rotation speed of 1000-3000 rpm for 15-30 seconds, a drying temperature of 60-80° C., a concentration of the dilute HF acid solution of 5wt%-15wt%, and an etching time of 10-15 minutes.

9. The method for preparing a GaAs / WSe2 heterojunction solar cell according to claim 5, characterized in that: The Au back electrode described in step 4 has a thickness of 100-120 nm and needs to be annealed to form an ohmic contact at a temperature of 300-350°C.

10. The method for preparing a GaAs / WSe2 heterojunction solar cell according to claim 5, characterized in that: Step 4: The cleaning solution of n-type GaAs is acetone, ethanol, and 10 wt% dilute hydrochloric acid. The soaking time in acetone is 10 to 15 minutes, and the drying temperature is 60 to 80°C.

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