Silicon Oxynitride Passivation Stack for Crystalline Silicon Solar Cells
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Solution Overview
Problem
Existing methods for passivating crystalline silicon solar cells face challenges with thermal stability and efficiency, particularly with dielectric materials like a-Si and SiOxNy, which degrade at high temperatures and result in increased production costs and reduced minority carrier lifetime.
Innovation Solution
A method involving the deposition of a silicon oxynitride layer at low temperatures (100° C. to 200° C.) using N2O and SiH4 precursor gases, followed by a hydrogenated dielectric capping layer, which enhances passivation and thermal stability, allowing for improved minority carrier lifetime and resistance to potential induced degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a-Si is used for passivation, then passivation quality is improved, but thermal stability deteriorates as a-Si loses passivation properties above 500°C
Solution Approach 1:
The patent applies composite materials by combining a-Si with SiO2 in a stacked configuration. The a-Si layer provides excellent passivation quality while the SiO2 layer contributes thermal stability. This composite structure allows the passivation stack to maintain low surface recombination velocity even after exposure to high temperatures above 500°C, resolving the contradiction between passivation quality and thermal stability.
Solution Approach 2:
The patent segments the passivation function into two distinct layers: an a-Si layer for optimal passivation and a SiO2 layer for thermal stability. This segmentation allows each material to perform its specialized function independently, with a-Si providing chemical passivation and SiO2 providing thermal protection, thereby achieving both high passivation quality and thermal stability simultaneously.
2Reliability
If thermal oxidation is used to grow SiO2 for passivation, then passivation quality is improved, but production cost increases due to high energy consumption and prolonged heating time
Solution Approach 1:
The patent replaces the thermal oxidation process with a chemical vapor deposition (CVD) process. Instead of using high-temperature thermal fields to grow SiO2, the invention uses a chemical deposition method where silicon-containing precursors react on the substrate surface to form SiO2. This substitution eliminates the need for prolonged high-temperature heating, significantly reducing energy consumption and production costs while maintaining passivation quality.
3Reliability
If SiNx is used for passivation on p-type silicon, then passivation is achieved, but parasitic shunting occurs due to high positive charge in the SiNx layer
Solution Approach 1:
The patent extracts the harmful positive charge component from the passivation system by replacing SiNx with a-Si/SiO2. The a-Si/SiO2 combination provides effective passivation without introducing the high positive charge that causes parasitic shunting in SiNx. This extraction of the harmful element (positive charge) while retaining the beneficial function (passivation) resolves the contradiction.
4Reliability
If Al2Ox is used for passivation, then excellent surface passivation is achieved, but manufacturing complexity increases due to requirements for very high vacuum and ALD process
Solution Approach 1:
The patent changes the deposition parameters and process conditions by using CVD instead of ALD. The a-Si/SiO2 stack can be deposited using standard CVD equipment and processes that are already widely used in solar cell manufacturing, eliminating the need for very high vacuum conditions and complex ALD processes. This parameter change maintains excellent surface passivation while dramatically reducing manufacturing complexity.
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
The method achieves significant improvements in passivation quality and thermal stability, resulting in a 0.4% absolute efficiency gain and enhanced resistance to potential induced degradation, while maintaining performance through high-temperature manufacturing steps.
Implementation Method 1
depositing, on at least a part of the cleaned surface, a layer of silicon oxynitride; wherein the layer of silicon oxynitride is deposited at a temperature from 100° C. to 200° C. using N2O and SiH4 as precursor gasses
Implementation Method 2
depositing a capping layer comprising a hydrogenated dielectric material on top of the layer of silicon oxynitride
Data Source
AI summary
A method for manufacturing a passivation stack on a crystalline silicon solar cell device. The method includes providing a substrate comprising a crystalline silicone layer such as a crystalline silicon wafer or chip, cleaning a surface of the crystalline silicon layer by removing an oxide layer at least from a portion of one side of the crystalline silicon layer, depositing, on at least a part of the cleaned surface, a layer of silicon oxynitride, and depositing a capping layer comprising a hydrogenated dielectric material on top of the layer of silicon oxynitride, wherein the layer of silicon oxynitride is deposited at a temperature from 100° C. to 200° C., and the step of depositing the layer of silicon oxynitride includes using N2O and SiH4 as precursor gasses in an N2 ambient atmosphere and depositing silicon oxynitride with a gas flow ratio of N2O to SiH4 below 2.