Process for reducing thermal spreading resistance loss for molybdenum oxide composite silicon heterojunction solar cells

Abstract

Molybdenum oxide (MoO X ) composite silicon heterojunction cell, choose wide band gap high work function transition metal oxide molybdenum oxide as hole selection layer, reduce the absorption of light surface, higher hole carrier export ability, and avoid the parasitic absorption caused by doping of the selection layer of traditional heterojunction cell, but the thermal stability of molybdenum oxide is poor, and the oxygen will diffuse to silicon when the temperature exceeds 130℃, which is the main obstacle to realize MoO X Composite silicon heterojunction solar cell applied to screen printing process to obtain larger light area and higher short circuit current. Therefore, we insert a layer of ZnO between a-Si:H(i) / MoO X After screen printing and annealing, ZnO prevents the mutual diffusion of MoO X And oxygen element in passivation layer, inhibits the opening pressure loss.

Description

Technical Field

[0001] This invention belongs to the field of solar cells and is a novel structure and process method for silicon-based heterojunction solar cells with improved thermal stability of molybdenum oxide composites. Background Technology

[0002] With rapid global economic development, energy demand has increased dramatically, leading to a rapid depletion of fossil fuel reserves. The extraction of traditional energy sources such as coal, oil, and natural gas is becoming increasingly difficult and costly, resulting in severe energy shortages in many countries. Simultaneously, over-reliance on fossil fuels has exacerbated environmental pollution and climate change, making the energy crisis not only a threat to economic stability but also a major challenge to the ecological environment and human health. Addressing the energy crisis is urgent and requires global cooperation to promote energy structure transformation and find sustainable energy development paths.

[0003] Crystalline silicon solar cells play a crucial role in modern energy conversion and are widely used in various solar power generation systems, favored for their high efficiency, stable performance, and long lifespan. In particular, heterocrystalline silicon solar cells, by combining amorphous and crystalline silicon, significantly improve photoelectric conversion efficiency and reduce energy loss. Their innovative technology not only enhances overall power generation efficiency but also drives advancements in solar energy technology, providing strong support for achieving more efficient and environmentally friendly energy utilization.

[0004] To achieve higher short-circuit currents in existing silicon-based heterojunction (SHJ) solar cells, current methods using selectively doped amorphous silicon and passivated intrinsic amorphous silicon to address parasitic absorption reduces the short-circuit current. Furthermore, the difficulty in doping p-type amorphous silicon limits the variation in work function, which remains a major obstacle to improving SHJ cell efficiency. Currently, the short-circuit current of high-efficiency SHJ cells is approximately 40 mA / cm². 2 To further reduce parasitic absorption losses and limited energy level tuning caused by the a-Si:H layer, high work function wide-bandgap oxides are an effective potential solution. This patent uses ZnO / MoO. X molybdenum oxide (MoO) structure X (This refers to) composite silicon heterojunction solar cells. This structure utilizes MoO2. X Wide bandwidth and high work function, while using ZnO to prevent MoO X The diffusion of oxygen in the screen-printed grid lines at the curing temperature reduces parasitic absorption losses and protects MoO. X It does not affect the transmission of holes. Summary of the Invention

[0005] This invention aims to solve the problem of MoO₂ in molybdenum oxide composite crystalline silicon heterojunction solar cells during the curing process of screen-printed grid lines. XThermal instability failure is an issue. Embodiments of this invention propose a method for fabricating a molybdenum oxide-surfaced screen-printed grid-type composite silicon-based heterojunction solar cell.

[0006] The method includes the following steps:

[0007] (1) A 3-5 nm intrinsic amorphous silicon thin film was deposited on one side of an n-type crystalline silicon substrate using plasma-enhanced chemical vapor deposition (PECVD) with SiH4 and H2 as reactant gases. Then, a 15-20 nm n-type microcrystalline silicon oxide thin film was deposited on the intrinsic amorphous silicon thin film using SiH4, H2, PH3 and CO2 as reactant gases.

[0008] (2) Using the PECVD method, SiH4 and H2 are used as reaction gases to deposit a 3-5 nm intrinsic amorphous silicon thin film on the other side of the crystalline silicon substrate. Then, a 2-3 nm ZnO thin film is deposited on the intrinsic amorphous silicon thin film by magnetron sputtering.

[0009] (3) A 9 nm molybdenum oxide film was grown on the ZnO film in step (2) by thermal dead oxidation sublimation.

[0010] (4) A 70 nm ITO film was prepared on the molybdenum oxide film in step (3) using reactive plasma (RPD);

[0011] (5) A 120 nm ITO film is deposited on the n-th thin film in step (1) using reactive plasma (RPD);

[0012] (6) After step (5) is completed, the silver electrode is thermally evaporated;

[0013] (7) Based on step (6), screen printing is used on the back side to screen print Ag electrodes on the p-side ITO thin film area and sinter and solidify at 200°C to complete the battery preparation.

[0014] This invention discloses a novel method for fabricating a molybdenum oxide composite silicon-based heterojunction solar cell with screen-printed grid electrodes. The method utilizes ZnO / MoO. X This structure replaces the doped amorphous silicon layer with a wide-bandgap molybdenum oxide, reducing parasitic absorption losses while possessing a high work function and better transport of hole carriers. Furthermore, ZnO is grown on the intrinsic amorphous silicon passivation layer, preventing thermal instability of the molybdenum oxide during the high-temperature curing process of the screen-printed grid lines. Through these optimizations of the traditional silicon heterojunction cell structure, the short-circuit current and open-circuit voltage of the cell are significantly improved. Moreover, the entire process remains unchanged compared to traditional heterojunction cells. Its fabrication method is simple and efficient, requiring no high-temperature annealing process, greatly reducing energy consumption. Attached Figure Description

[0015] Figure 1This is a structural diagram of the battery according to an embodiment of the present invention; 1 is a silver grid line, 2 is ITO, 3 is molybdenum oxide, 4 is zinc oxide, 5 is an intrinsic amorphous silicon passivation layer, 6 is a crystalline silicon substrate, 7 is n-type microcrystalline silicon oxide, and 8 is a silver electrode.

[0016] Figure 2 This is a flowchart illustrating the battery manufacturing process according to an embodiment of the present invention;

[0017] Figure 3 The optical JV curve of the prepared battery; Detailed Implementation

[0018] This invention relates to a method for ZnO / MoO X A method for fabricating composite silicon-based heterojunction solar cells. Examples or illustrative examples disclosed below are used to implement different structures of the present invention. To simplify the disclosure of the present invention, only specific components and arrangements are described below. Example

[0019] refer to Figure 2 , Figure 2 This is a flowchart illustrating the battery manufacturing process according to an embodiment of the present invention.

[0020] (1) In step 101, pure SiH4 and H2 are used as reaction gases to deposit intrinsic amorphous silicon 3-5 nm on a clean single-crystal silicon substrate. Then, n-type microcrystalline silicon oxide is deposited on the intrinsic amorphous silicon. The conditions for PECVD preparation of intrinsic amorphous silicon are: background vacuum is below 10 -3 Pa, substrate temperature 200℃, SiH4 gas flow rate 75 sccm, H2 flow rate 70 sccm, pressure 0.7 mbar, deposition power 100 mW / cm² 2 The prepared intrinsic amorphous silicon has a thickness of 3-5 nm. The conditions for PECVD preparation of n-type microcrystalline silicon oxide are: background vacuum below 10... -3 Pa, substrate temperature 200℃, SiH4 gas flow rate 75 sccm, CO2 flow rate 5 sccm, hydrogen-diluted PH3 (PH3 concentration 20%) flow rate 15 sccm, pressure 0.7 mbar, deposition power 200 mW / cm² 2 The thickness of the prepared n-type microcrystalline silicon oxide is 15-20 nm.

[0021] (2) In step 102, intrinsic amorphous silicon is deposited on the other side of the n-type crystalline silicon substrate. The conditions for preparing intrinsic amorphous silicon are the same as the deposition parameters in step 101.

[0022] (3) In step 103, ZnO of 2-3 nm is deposited again on the intrinsic amorphous silicon deposited in step 102 by magnetron sputtering. The specific process conditions are: pressure 0.4 Pa, argon flow rate 30 sccm, sputtering power 150 W, and target material ZnO.

[0023] (4) In step 104, after the ZnO thin film deposition, a 9 nm MoO film is prepared using a hot filament oxidation-sublimation method. X The specific process conditions are: pressure 4×10 -8 Pa, evaporation power supply current is 40A, oxygen flow rate is 20sccm, and deposition rate is 8nm / min.

[0024] (5) In step 105, hydrogen-doped ITO thin films are deposited on both sides respectively. The specific process conditions are: pressure 0.4 Pa, argon flow rate 50 sccm, oxygen flow rate 30 sccm, hydrogen flow rate 30 sccm, DC power density 300 mW / cm, and target material is indium tin oxide (90% indium oxide and 10% tin oxide), where the n side is 120 nm and the p side is 70 nm.

[0025] (6) In step 106, Ag is first vapor-deposited on the n-side, and then silver grid lines are screen-printed on the p-side, where the fine grid is 30µm and the main grid is 600µm. Then, the grid lines are annealed at 200℃ for 3 minutes to complete the grid line curing.

[0026] Figure 3 This is the JV curve of the battery prepared by this method. The open-circuit voltage of the battery reaches 700mV, and the short-circuit current is 38.37mA / cm. 2 The conversion efficiency is 19.36%.

Claims

1. A method for fabricating silicon-based heterojunction solar cells using screen printing of MoOx composites, characterized in that, Includes the following steps: (1) Using plasma-enhanced chemical vapor deposition (PECVD), SiH4 and H2 are used as reactants to deposit a 3-5 nm intrinsic amorphous silicon thin film on one side of an n-type crystalline silicon substrate. Then, using SiH4, H2, PH3 and CO2 as reactants, a 15-20 nm n-type microcrystalline silicon oxide thin film is deposited on the intrinsic amorphous silicon thin film, i.e., the back side and the n side. (2) Using the PECVD method, SiH4 and H2 are used as reaction gases to deposit a 3-5 nm intrinsic amorphous silicon thin film on the other side of a crystalline silicon substrate, and then a 2-3 nm ZnO thin film is sputtered by magnetron sputtering. (3) A 9 nm MoOx thin film was deposited on ZnO using the hot filament oxidation sublimation method (HWOSD); (4) Based on steps (2) and (3), hydrogen-doped ITO thin films are prepared on both sides using reactive plasma (RPD); (5) After step (4) is completed, silver is vapor-deposited on the n-side; (6) Silver grid lines were screen printed on the ITO film on the MoOx side and cured to complete the battery preparation.

2. The method according to claim 1, characterized in that... In step (2), the Ar gas flow rate for magnetron sputtering is 30 sccm, and the growth rate is controlled below 8 nm / min.

3. The method according to claim 1, characterized in that... In step (3), the oxygen flow rate during growth is 10 sccm.

4. The method according to claim 1, characterized in that... The TCO thickness in step (4) is 70 nm on the p-side and 120 nm on the n-side.

5. The method according to claim 1, characterized in that... The silver grid lines prepared by screen printing in step (6) have a fine grid line width of 30 micrometers and a main grid line width of 600 micrometers.

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