Preparation method of novel hole transport layer zinc telluride

Abstract

The application discloses a preparation method of a novel hole transport layer zinc telluride, and the method comprises the following steps: placing a Si sheet after cleaning above a cavity of a thermal evaporation film plating machine, closing a baffle, connecting a tungsten boat below the cavity, placing ZnTe powder on the tungsten boat, and vacuumizing; controlling the current and voltage passing through the tungsten boat to regulate the growth rate, opening the cavity baffle to grow a film with a corresponding thickness; closing the thermal evaporation film plating machine and taking a sample, and cleaning the surface with nitrogen. The valence band of the ZnTe film grown by thermal evaporation and the valence band of an n-Si substrate have a low valence band band gap, so that the hole transport performance can be improved; because the ZnTe is p-type and can be doped, the work function of the ZnTe can be regulated by using a metal, so that the charge transport capacity can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of solar cells, in particular to a preparation method of a novel hole transport layer zinc telluride. BACKGROUND

[0002] As one of the most potential new energy, solar cells have attracted more and more attention. Factors affecting the efficiency of the cell include collection probability, photo-generation rate, characteristic resistance, temperature, light intensity, etc. To enhance the light energy conversion rate, various energy losses need to be reduced. Considering the manufacturing cost and the difficulty of passivation, etc., the research focuses on how to reduce the electrical loss of the solar cell. With the in-depth study of high-efficiency crystalline silicon solar cells, it is found that reducing various types of recombination is the key to improving the efficiency.

[0003] Passivated contact can effectively reduce the recombination rate of photo-generated carriers, which is divided into chemical passivation and field passivation. Chemical passivation refers to saturating various defect states at the interface to reduce the interface defect concentration, thereby reducing the recombination center in the forbidden band, which can be realized by inserting silicon oxide (SiO x ) or intrinsic amorphous silicon (a-Si:H); field effect passivation, that is, through charge accumulation, an electrostatic field is formed at the interface to reduce the minority carrier concentration, for example, aluminum oxide (AlO x ) has a negative charge and can be used to passivate the p-type region, or a material with an extreme work function is used to contact the crystalline silicon to form a potential barrier region to extract electrons or holes.

[0004] At present, the hole transport layer (HTL) of crystalline silicon heterojunction solar cells is completed by using doped amorphous silicon (p a-Si:H), which uses field passivation formed by work function difference to improve the efficiency of the cell. However, the band gap of p a-Si:H is not large, which causes strong parasitic absorption and affects the photoelectric conversion of the cell. Metal compounds can be used to replace p / n a-Si:H. At present, the HTL is mostly transition metal oxide (TMO), such as MoO x , WO x , V2O x and NiO x , etc. Such materials have the advantages of large forbidden band width and small parasitic light absorption, and most of the TMOs can avoid the use of flammable, explosive and toxic gases, and are safer. Among the ways to grow TMO, the thermal evaporation and electron beam evaporation methods have the advantage of low cost; ALD can accurately control the film composition and thickness; magnetron sputtering can control O vacancies in a large range; solution method can change the O vacancies of the material through subsequent low-temperature annealing.

[0005] MoO xMoO x The position of the valence band top is far from that of crystalline silicon (c-Si) or intrinsic amorphous silicon (i-a-Si:H), thus a potential barrier region is generated to hinder the conduction of holes, which affects the hole Fermi level and reduces the open-circuit voltage of the battery.

[0006] ZnTe has a band gap of 2.26 eV in the crystalline state, a high work function, and high doping, and is used as a buffer layer in CdTe batteries, but has not been applied as a hole transport layer in crystalline silicon heterojunction battery fields. The growth method can be controlled to have a suitable energy band structure that matches the crystalline silicon, so it is hoped that it can be applied to crystalline silicon batteries to expand the new field to be explored. SUMMARY

[0007] To overcome the deficiencies of the prior art, the present application provides a preparation method of a novel hole transport layer of zinc telluride. High-performance hole selective contact must first ensure that the hole Fermi level of the hole transport layer is consistent with the hole Fermi level of the contact layer. When the valence band position is lower than the valence band top of the substrate, a potential barrier is generated at the interface, the p-type layer is depleted, and the energy band edge is sharply curved upward. Under light, the resistivity of the depletion layer is high, so the hole Fermi level is also curved upward, and the thickness of the p-type layer can approach the electron Fermi level. This case can be replaced by a thinner or higher mobility hole transport layer.

[0008] When the valence band position is higher than the valence band top of the substrate, the depletion region is mainly concentrated on the substrate side, and the hole chemical potential changes at the c-Si / p-type layer interface, and then remains relatively stable, but the difference between the electron and hole Fermi levels in the p-type layer is still reduced. Secondly, the doping concentration of the hole transport layer also affects the transmission of holes. As the doping concentration rises, the hole Fermi level gradually rises, and a high doping concentration also causes the depletion layer region of the p-type layer to narrow, thus improving the conductivity of the entire p-type layer. Therefore, in the process of selecting a hole transport layer, in addition to considering a high work function and a high band gap, the valence band top energy that matches the substrate and the doping of the material should also be considered.

[0009] The present application is The lower rate of growth of the zinc telluride film is below 10 nm, so the material exhibits amorphous characteristics. The amorphous ZnTe has a new energy band structure, and the band gap is 3.1 eV measured by the Tauc Plot method, which is lower than the valence band of c-Si.

[0010] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0011] The first aspect of the present application provides a preparation method of a novel hole transport layer zinc telluride, comprising the following steps:

[0012] After the Si sheet is cleaned, it is placed above the cavity of the thermal evaporation coating machine, the baffle is closed, a tungsten boat is connected below the cavity, ZnTe powder is placed on the tungsten boat, and vacuum is extracted; the growth rate is controlled by controlling the current and voltage passing through the tungsten boat, the baffle of the cavity is opened to grow a thin film of a corresponding thickness; the thermal evaporation coating machine is closed and the sample is taken out, and the surface is cleaned with nitrogen.

[0013] Preferably, the Si sheet is cleaned using RCA 1, RCA 2 and HF solution, specifically comprising the following steps:

[0014] (1) The RCA 1 solution is heated to 70-90℃, the Si sheet is placed in, heated for 5-15 min, taken out, and washed with deionized water; the Si sheet is placed in the HF solution, taken out after 30 s-1 min, washed with deionized water, and dried with nitrogen.

[0015] (2) The RCA 2 solution is heated to 70-90℃, the Si sheet is placed in, heated for 5-15 min, taken out, and washed with deionized water; the Si sheet is placed in the HF solution, taken out after 30 s-1 min, washed with deionized water, and dried with nitrogen.

[0016] Preferably, the RCA 1 solution is prepared by mixing 25wt%-28wt% ammonia solution, 28wt%-32wt% hydrogen peroxide solution and deionized water in a volume ratio of 1:1:(5-7); further preferably, the RCA 1 solution is prepared by mixing 25wt%-28wt% ammonia solution, 28wt%-32wt% hydrogen peroxide solution and deionized water in a volume ratio of 1:1:6.

[0017] Preferably, the RCA 2 solution is prepared by mixing 36wt%-38wt% hydrochloric acid solution, 28wt%-32wt% hydrogen peroxide solution and deionized water in a volume ratio of 1:1:(5-7); further preferably, the RCA 2 solution is prepared by mixing 36wt%-38wt% hydrochloric acid solution, 28wt%-32wt% hydrogen peroxide solution and deionized water in a volume ratio of 1:1:6.

[0018] The concentration of the HF solution is greater than or equal to 40wt%; the purity of the drug used in the application is greater than or equal to AR.

[0019] Preferably, the vacuum is controlled to be less than or equal to 7.5x10 -4 Pa.

[0020] Preferably, the voltage of the tungsten boat is controlled to be 0.3-0.4V, and the current is controlled to be 45-55A; further preferably, the voltage of the tungsten boat is controlled to be 0.37V, and the current is controlled to be 48-52A, and the evaporation rate of ZnTe is controlled to be 0.3-0.4A.

[0021] Preferably, the temperature of the substrate during the coating process is less than or equal to 50℃.

[0022] The second aspect of the application provides a zinc telluride film prepared by the preparation method of the novel hole transport layer zinc telluride.

[0023] Preferably, the thickness of the zinc telluride film is less than or equal to 10nm.

[0024] Preferably, the zinc telluride film is amorphous, and the band gap is 2.8-3.4eV.

[0025] Compared with the prior art, the application has the following beneficial effects:

[0026] The valence band of the ZnTe film grown by thermal evaporation and the valence band of the n-Si substrate have a low valence band band gap, so that the hole transport performance can be improved; due to the p-type doping property of ZnTe, the work function of the metal can be regulated to some extent, and the charge transport capacity can be improved. DETAILED DESCRIPTION

[0027] The specific embodiments of the application will be further described below. It should be noted that the description of these embodiments is used to help understand the application, but does not constitute a limitation on the application. In addition, the technical features involved in each embodiment of the application described below can be combined with each other as long as they do not conflict with each other.

[0028] The experimental methods in the following examples are all conventional methods unless otherwise specified. The test materials used in the following examples are all commercially available unless otherwise specified.

[0029] Example 1

[0030] (1) Cut the n-type c-Si according to a certain size;

[0031] (2) Prepare the solution: including RCA 1, RCA2 and HF solution;

[0032] RCA 1 (ammonia: hydrogen peroxide: deionized water = 1:1:5, remove organic matter on the surface of the silicon wafer);

[0033] RCA 2 (hydrochloric acid: hydrogen peroxide: deionized water = 1:1:5, remove metal impurities on the surface of the silicon wafer);

[0034] HF solution (hydrofluoric acid: water = 1:20, remove oxide on the surface of the silicon wafer);

[0035] (3) Heat RCA 1 to 80°C, put it into the silicon wafer basket, heat for 10 min, take out the basket, and rinse it with deionized water for 2-3 times;

[0036] (4) Put the Si wafer into the HF solution, take it out after 30 s-1 min, rinse it with deionized water for 2-3 times;

[0037] (5) Heat RCA 2 to 80°C, put it into the silicon wafer, heat for 10 min, take out the basket, and rinse it with deionized water for 2-3 times;

[0038] (6) Put the Si wafer into the HF acid solution, take it out after 1 min, rinse it with deionized water for 2-3 times, and dry it with nitrogen;

[0039] (7) Put the Si into the cavity of the thermal evaporation coating machine, connect the positive and negative electrodes with a tungsten boat below the cavity, put ZnTe powder on the tungsten boat, close the cavity and vacuumize it to below 7.5E-4 Pa;

[0040] (8) Adjust the voltage to 0.37 V, and the current to about 50 A, at this time the evaporation rate of ZnTe is about 0.37 V / 50 A = 7.4 A / cm2; The substrate temperature is kept below 50°C, and the growth is continued until the desired thickness is reached.

[0041] The above hydrofluoric acid is AR, ≥40%, the ammonia is AR, 25%-28%, the hydrogen peroxide is AR, 30%, the hydrochloric acid is AR, 36%-38%, and the thermal evaporation coating machine is QHV-R53 type thermal evaporation coating machine.

[0042] The embodiments of the present application are described in detail above, but the present application is not limited to the described embodiments. For those skilled in the art, various changes, modifications, replacements and variations of the embodiments can be made without departing from the principles and spirits of the present application, and still fall within the protection scope of the present application.

Claims

1. A method for preparing zinc telluride hole transport layer, characterized in that, Includes the following steps: After cleaning the Si wafer, place it above the cavity of the thermal evaporation coating machine, close the baffle, connect a tungsten boat below the cavity, place ZnTe powder on the tungsten boat, and evacuate the vacuum. Control the current and voltage through the tungsten boat to regulate the growth rate, open the cavity baffle to grow a thin film with a thickness ≤10nm, turn off the thermal evaporation coating machine and take a sample, and clean the surface with nitrogen. The voltage of the tungsten boat is 0.3-0.4V, and the current is 45-55A; The evaporation rate of ZnTe was controlled to be 0.09–0.11 Å / s; The thin film is amorphous and has a band gap of 2.8-3.4 eV.

2. The method for preparing zinc telluride hole transport layer according to claim 1, characterized in that, The Si wafer is cleaned using RCA 1, RCA 2, and HF solutions, specifically including the following steps: (1) Heat the RCA 1 solution to 70-90℃, put in the Si wafer, heat for 5-15 min, take it out and rinse with deionized water; put the Si wafer in HF solution, take it out after 30 s - 1 min, and rinse with deionized water; (2) Heat the RCA 2 solution to 70-90℃, put in the Si wafer, heat for 5-15 min, take it out and rinse with deionized water; put the Si wafer into the HF solution, take it out after 30s-1min, rinse with deionized water and blow dry with nitrogen.

3. The method for preparing zinc telluride hole transport layer according to claim 2, characterized in that, The RCA 1 solution is prepared by mixing 25wt%-28wt% ammonia solution, 28wt%-32wt% hydrogen peroxide solution, and deionized water in a volume ratio of 1:1:(5-7).

4. The method for preparing zinc telluride hole transport layer according to claim 2, characterized in that, The RCA 2 solution is prepared by mixing 36wt%-38wt% hydrochloric acid solution, 28wt%-32wt% hydrogen peroxide solution, and deionized water in a volume ratio of 1:1:(5-7).

5. The method for preparing zinc telluride hole transport layer according to claim 1, characterized in that, The vacuum was evacuated to 7.5 × 10⁻⁶. -4 Below Pa.

6. The method for preparing zinc telluride hole transport layer according to claim 1, characterized in that, During the coating process, the substrate temperature is ≤50℃.

7. A zinc telluride thin film, characterized in that, It is prepared by the method for preparing the hole transport layer zinc telluride according to any one of claims 1-6.