Multi-Layer AlOx Back Passivation for Faster PECVD Solar Cells
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Solution Overview
Problem
The existing AlOx passivation films in solar cells, particularly those prepared by PECVD, suffer from inadequate surface chemical and field passivation effects, leading to suboptimal conversion efficiency, and can damage the silicon wafer substrate during the plasma-based deposition process.
Innovation Solution
A multi-layer AlOx film is developed, where each layer is treated with NH3 and N2O, with the bottom layer prepared under low deposition speed and high oxygen conditions to increase negative charge density, and the top layer at higher speeds to enhance field passivation without extending the process time, combined with thermal oxidation and annealing to improve silicon oxide compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If PECVD method is used to prepare AlOx passivation film, then film-forming rate is high and process flexibility is improved, but surface chemical passivation effect and field passivation effect are insufficient
Solution Approach 1:
The AlOx passivation film is divided into multiple sub-layers with different deposition conditions. Each sub-layer has optimized parameters for specific functions (surface passivation or field passivation), allowing the overall film to achieve both high formation rate and excellent passivation效果 through functional segmentation
Solution Approach 2:
Different regions of the AlOx film are prepared with different local properties by varying deposition parameters at different stages. The early-stage sub-layers have higher oxygen content for surface chemical passivation, while later sub-layers have different characteristics for field passivation, achieving localized optimization throughout the film structure
2Productivity
If PECVD plasma process is used for AlOx deposition, then deposition speed is improved, but silicon wafer substrate is damaged and surface chemical passivation is destroyed
Solution Approach 1:
A silicon oxide layer is prepared on the silicon wafer substrate before AlOx deposition. This preliminary layer acts as a protective buffer that prevents plasma damage to the substrate while allowing subsequent AlOx film deposition to proceed at high speed
Solution Approach 2:
The deposition process uses periodic pulsed PECVD cycles with alternating plasma on and off periods. During plasma off periods, the substrate is protected from continuous plasma bombardment, while during plasma on periods, rapid AlOx deposition occurs, achieving both high speed and reduced damage through time-separated actions
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves the overall passivation effect, increases the negative charge density, and enhances the conversion efficiency of solar cells by 0.05-0.10% while minimizing substrate damage.
Implementation Method 1
PECVD is a technique using plasma to activate a reactive gas to promote a chemical reaction at a surface or a near-surface space of a substrate to form a solid film
Implementation Method 2
plasma-enhanced chemical vapor deposition (PECVD)... The basic principle of PECVD is that the plasma is formed by ionizing a source gas under the action of a high-frequency or direct-current electric field
Implementation Method 3
each layer of the AlOx film is treated with NH3 and N2O
Implementation Method 4
combined with thermal oxidation and annealing to improve silicon oxide compactness
Implementation Method 5
combined with thermal oxidation and annealing to improve silicon oxide compactness
Data Source
AI summary
The present disclosure relates to the technical field of solar cell preparation, and provides a solar cell, an AlOx depositing method therefor, and a cell back passivation structure and method. In the present disclosure, a silicon wafer which has been subjected to thermal oxidization and annealing is placed into a tubular PECVD equipment. The chamber is vacuumized to a pressure of 100-2000 mTorr and heated to a temperature of 300-400° C. Then nitrous oxide and TMA as reaction gases are introduced in to the chamber. The radio-frequency power supply is turned on and an AlOx passivation film having two-layer, three-layer, or more-layer film structure is prepared.