Hydrogen-treated titanium nitride electron selective contact material applied to crystalline silicon solar cell and preparation method of hydrogen-treated titanium nitride electron selective contact material

Abstract

The invention belongs to the technical field of materials, and particularly relates to a hydrogen-treated titanium nitride electron selective contact material applied to a crystalline silicon solar cell and a preparation method of the hydrogen-treated titanium nitride electron selective contact material. The method comprises the steps that a TiN film is prepared by introducing mixed working gas with the ratio of Ar gas to H2 gas being 95: 5 through radio frequency magnetron sputtering, and annealing is conducted at the temperature of 250 DEG C in the atmosphere with the ratio of Ar gas to H2 gas being 95: 5. The material is prepared on the back surface of a crystalline silicon solar cell as an electron selection contact layer, so that the electron extraction efficiency is improved, the interface recombination of current carriers is reduced, and the photoelectric conversion efficiency of the solar cell is improved. The preparation process is rapid, simple and convenient, the material cost is low, and the obtained material can be applied to the fields of crystalline silicon solar cells or perovskite / crystalline silicon laminated solar cells and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of materials, and particularly relates to a hydrogen-treated titanium nitride electron selective contact material applied to crystalline silicon solar cells and a preparation method thereof. Background Art

[0002] Monocrystalline silicon solar cells dominate the civilian photovoltaic market due to their stability, high photoelectric conversion efficiency, and low cost. However, the amorphous silicon carrier selective contact layer formed by boron / phosphorus diffusion has a parasitic absorption problem due to its narrow bandgap and doping. Therefore, further selection of undoped electron selective contact materials with a wider bandgap and lower parasitic absorption has been proposed as a substitute for the doped layer in various types of solar cells. Generally, such materials are mainly transition metal oxides and nitrides. However, their film contact resistivity and film resistance are not low enough, which results in a not-high-enough fill factor of the solar cell, and due to the passivation performance when such materials are in contact with crystalline silicon, the open circuit voltage of the solar cell is low.

[0003] Therefore, the patent inventor developed a process of adding hydrogen passivation during the preparation of the electron selective contact material and compared the performance differences of titanium nitride materials with and without hydrogen passivation under the annealing process. The invention points out that the annealing process using a titanium nitride film without hydrogen should be adopted to improve the contact passivation level of crystalline silicon solar cells. This invention provides a new solution for the application of highly conductive undoped nitride electron selective contact materials in crystalline silicon cells and also has broad application prospects. Summary of the Invention

[0004] Aiming at the problem of insufficient contact passivation between undoped materials and crystalline silicon, the purpose of the present invention is to provide two methods of hydrogen implantation and regulate the titanium / nitrogen content ratio of the titanium nitride material to achieve the two goals of carrier selective contact and passivation.

[0005] To achieve the above object, the main technical solutions adopted by the present invention include: The present invention provides a regulation method for a titanium nitride selective contact material with magnetron sputtering as the core preparation process, which includes the following steps: 1) Using n type monocrystalline silicon wafers as substrates for cleaning and texturing, and performing boron diffusion by a diffusion process; 2) Wet etching to remove boron-silicate glass and the p area on the back surface; 3) Using atomic layer deposition to deposit alumina on the front surface; 4) Using low-pressure chemical vapor deposition to continue depositing silicon nitride on the above alumina; 5) Screen printing on the above silicon nitride to prepare the front electrode; 6) Remove other oxides and nitride wrap coatings other than polysilicon on the back surface with hydrofluoric acid vapor; 7) Cover and protect the front surface of the above sample, and oxidize the back surface in an oxygen plasma environment; 8) Use a TiN target with a purity higher than 99.95%, and deposit a titanium nitride thin film on the back surface under the condition that the background vacuum of magnetron sputtering is better than 5×10 -4 Pa; 9) Transfer the above sample to a tube furnace and evacuate it to vacuum. Anneal it at 250 °C in a mixed gas of Ar and H2 with a ratio of 95:5; 10) Continuously deposit a lithium fluoride thin film on the aforementioned titanium nitride thin film; 11) Deposit an aluminum thin film electrode on the aforementioned lithium fluoride thin film.

[0006] In the present invention, hydrogen implantation affects the actual element ratio of TiN when exposed to air, realizing the electron selective contact and passivation of the undoped nitride in the crystalline silicon battery. On the one hand, hydrogen implantation during the preparation of TiN reduces the oxidation of TiN in the atmosphere and also passivates the interface defects at the contact between TiN and crystalline silicon; on the other hand, hydrogen implantation can be carried out by subsequent annealing in a mixed gas of Ar and H2 with a ratio of 95:5 at 250 °C to secondarily optimize the hydrogen passivation at each thin film and interface of the battery. The different selection results improve the efficiency of the undoped TiN electron selective contact passivated solar cell.

[0007] The core operation in the above steps is the preparation of the carrier selective contact layer of TiN. Since TiN is extremely easy to be oxidized in air, the work function increases, which has a negative effect on inducing the bending of the crystalline silicon energy band to better extract electrons. Therefore, it is very important to incorporate hydrogen during the preparation of TiN to control the oxidation degree and maintain the ratio of Ti atoms and N atoms. In addition, during the subsequent annealing with hydrogen, attention should be continuously paid to whether hydrogen bonds with Ti or Si for passivation. Because if it bonds with Ti excessively and then enters the air through a high-temperature environment, it will induce the transformation of titanium nitride to titanium oxide, resulting in an increase in the work function of the material and failure to passivate defects, which is a negative effect. Description of the Drawings

[0008] Figure 1 It is a schematic diagram of the structure of the solar cell of the present invention.

[0009] Figure 2 It is the current-voltage characteristic curve of the solar cell in Example 1 and the result of the work function characterized by ultraviolet photoelectron spectroscopy.

[0010] Figure 3 It is the current-voltage characteristic curve of the solar cell in Example 2 and the result of the work function characterized by ultraviolet photoelectron spectroscopy. Detailed Embodiments

[0011] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Embodiment 1

[0012] In this embodiment, the crystalline silicon cell structure is as Figure 1 shown, and successively includes from top to bottom: a metal grid electrode (Ag / Al), an antireflection layer (SiN x ), a passivation layer (AlO x ), p an emitter, n a p-type textured substrate, a silicon oxide layer, an electron selective contact layer (TiN), and a full-area metal electrode (Al).

[0013] The solar cell of this embodiment is obtained through the following preparation method: 1) Using a n p-type single crystal silicon wafer as a substrate for cleaning and texturing, with a final thickness of 140 ± 14 μm, and performing boron diffusion by a diffusion process; 2) Wet etching to remove the boron-silicate glass and the p B area on the back surface; 3) Using atomic layer deposition to deposit a continuous film of about 10 nm of aluminum oxide on the front surface; 4) Using low-pressure chemical vapor deposition to continue depositing a continuous film of about 80 nm of silicon nitride on the above-mentioned aluminum oxide; 5) Screen printing on the above-mentioned silicon nitride to prepare the front electrode; 6) Using hydrofluoric acid vapor to remove other oxides and nitride overcoatings except silicon on the back surface; 7) Covering and protecting the front surface of the above-mentioned sample, and exposing the back surface to an oxygen plasma environment for oxidation, with a process treatment time of 15 s, a radio frequency power of 25 W, and an oxygen flow rate of 40 sccm; 8) Using a TiN target with a purity higher than 99.95%, sputtering with a mixed gas of Ar gas and H2 gas with a ratio of 95:5 as the working gas under the condition that the background vacuum of magnetron sputtering is better than 5×10 -4 Pa, depositing a titanium nitride film of about 5 nm on the back surface, with a radio frequency power of 120 W and a working pressure of 0.2 Pa; 9) Continuing to deposit a lithium fluoride film of about 1.5 nm on the above-mentioned titanium nitride film; 10) Depositing an aluminum film electrode of about 200 nm on the above-mentioned lithium fluoride film.

[0014] The current-voltage characteristic curve of the solar cell of this embodiment and the work function of the hydrogen-implanted TiN film (3.87 eV) are as Figure 2As shown, the photoelectric conversion efficiency reaches 20.7%. The ratio of Ti element to N element calibrated by X-ray photoelectron spectroscopy is about 1. Under this condition, the sheet resistance of the TiN thin film at 150 nm is 17.1 Ω / sq. Example 2

[0015] In this example, the crystalline silicon cell structure is as Figure 1 shown, and successively includes from top to bottom: a metal grid electrode (Ag / Al), an antireflection layer (SiN x ), a passivation layer (AlO x ), p an emitter, n a p-type textured substrate, a silicon oxide layer, an electron selective contact layer (TiN), and a full-area metal electrode (Al).

[0016] The preparation method of the solar cell in this example is the same as the first 7 steps in Example 1. Subsequently, the preparation process is as follows: 8) Using a TiN target with a purity higher than 99.95%, sputtering is carried out using Ar as the working gas under the condition that the background vacuum of magnetron sputtering is better than 5×10 -4 Pa, and a titanium nitride thin film of about 5 nm is deposited on the back surface. The radio frequency power is 120 W, and the working pressure is 0.2 Pa; 9) Transfer the above sample to a tube furnace and evacuate it to vacuum. Anneal it at 250°C for 30 minutes in a mixed gas of Ar gas and H2 gas with a ratio of 95:5; 10) Continuously deposit a lithium fluoride thin film of about 1.5 nm on the aforementioned titanium nitride thin film; 11) Deposit an aluminum thin film electrode of about 200 nm on the aforementioned lithium fluoride thin film.

[0017] The current-voltage characteristic curve of the solar cell in this example and the work function of the hydrogen-implanted TiN thin film (3.82 eV) are as Figure 3 shown. The photoelectric conversion efficiency reaches 22.2%. The ratio of Ti element to N element calibrated by X-ray photoelectron spectroscopy is about 1. Under this condition, the sheet resistance of the TiN thin film at 150 nm is 14.7 Ω / sq.

[0018] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. 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 should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A hydrogen-treated titanium nitride electron-selective contact material for crystalline silicon solar cells and a preparation method thereof, characterized in that, It includes the following steps: S1: SiO x Layer preparation Place the crystalline silicon solar cell with the front side (light-incident side) prepared and the other side being bare silicon (backlight side) in a magnetron sputtering chamber. Then, evacuate the chamber vacuum to below 5×10 -4 Pa, and then introduce oxygen with a purity of 99.999%. Connect a 13.56 MHz radio frequency power supply to the capacitive cathode and start the glow discharge at a certain power. Treat the bare silicon surface of the sample for a certain period of time. After the silicon surface is treated with oxygen plasma, a SiO x layer is formed; S2: Preparation of hydrogen-containing TiN electron selective layer Place the sample that has completed S1 in a magnetron sputtering chamber with a vacuum degree pumped down to below 5×10 -4 Pa, connect a TiN target (purity ≥ 99.95%) to a 13.56 MHz radio frequency power supply, introduce a mixed gas of Ar gas and H2 gas with a ratio of 95:5 to initiate glow discharge, and prepare a hydrogen-containing passivated TiN electron selective layer; S3: Preparation of hydrogen-free TiN electron selective layer Place the sample that has completed S1 in a magnetron sputtering chamber with a vacuum degree pumped down to below 5×10 -4 Pa, connect a TiN target (purity ≥ 99.95%) to a 13.56 MHz radio frequency power supply, introduce Ar gas to initiate glow discharge, and prepare a hydrogen-free passivated TiN electron selective layer; S4: Overall annealing of the device The device with the prepared SiO x / TiN electron-selective contact passivation layer is placed in a mixed gas of Ar and H2 with a ratio of 95:5 for high-temperature annealing.

2. The crystalline silicon solar cell according to claim 1, wherein: Selection of silicon thin film n Type of single crystal silicon wafer, with the silicon wafer morphology being single-sided texturing and single-sided polishing.

3. The crystalline silicon solar cell according to claim 1, characterized in that: This solar cell is a single-sided light-receiving cell.

4. The crystalline silicon solar cell according to claim 1, wherein: In the single-sided light-receiving cell, the light-receiving surface of the cell uses metal grid lines as electrodes and adopts a laser-enhanced contact optimization process, and the backlight surface uses full metal as electrodes.

5. A hydrogen-treated titanium nitride electron-selective contact material for crystalline silicon solar cells and a preparation method thereof, characterized in that: The passivation quality of the contact between crystalline silicon and the electron selective layer is improved through two hydrogen treatment methods, so that the photoelectric conversion efficiency of the crystalline silicon solar cell using the undoped material exceeds 22%, and the ratio of Ti element to N element of this thin film calibrated by X-ray photoelectron spectroscopy is about 1.

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