Crystalline Silicon Solar Cell Texture Cleaning via HCl and Ozone
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Solution Overview
Problem
The use of rounded texture recesses on crystalline silicon substrates for solar cells improves open circuit voltage and fill factor but reduces the anti-reflection effect, leading to a decrease in short circuit current and overall conversion efficiency, especially when the texture size is small and density is high. Additionally, existing ozone cleaning methods are inefficient and environmentally costly due to high ozone waste generation.
Innovation Solution
A method involving anisotropic etching followed by hydrochloric acid treatment and ozone treatment maintains the texture shape, reducing impurity deposition and maintaining high cleanliness and optical confinement, while bubbling ozone gas into the water bath enhances cleaning efficiency and reduces waste.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If isotropic etching is performed to round recesses of texture, then open circuit voltage and fill factor are improved, but anti-reflection effect is reduced leading to decreased short circuit current
Solution Approach 1:
The patent applies preliminary action by performing isotropic etching with oxidizing aqueous solution before the main ozone treatment step. This preliminary etching rounds the recesses of the texture to improve open circuit voltage and fill factor, while the subsequent ozone treatment restores the anti-reflection effect by removing oxidation products and cleaning the surface, thus preventing the harmful effect of reduced short circuit current
2Reliability
If conventional ozone treatment is used for cleaning, then surface cleanliness is improved, but large amount of ozone waste is generated increasing treatment cost and environmental load
Solution Approach 1:
The patent applies parameter changes by optimizing the ozone concentration in the ozone water bath to a specific range (1-10 ppm) and controlling the treatment time. This parameter optimization achieves effective surface cleaning while minimizing ozone consumption and waste generation. The method also recycles the ozone water after treatment, further reducing ozone waste and environmental impact
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 results in a crystalline silicon substrate with improved cleanliness and optical confinement, enhancing the conversion efficiency of solar cells by maintaining the anti-reflection effect and reducing impurity deposition, with a more environmentally friendly ozone treatment process.
Implementation Method 1
a surface of a silicon substrate is anisotropically etched to form a quadrangular pyramid-shaped (pyramidal) concave-convex structure so called texture
Implementation Method 2
isotropic etching is then performed using an oxidizing aqueous solution such as HF/HNO3, so that recesses of the texture are rounded
Implementation Method 3
a treatment is performed to round recesses of the texture, and a single-crystalline silicon substrate is then immersed in ozone water to form an oxide film. When the silicon substrate after formation of the oxide film is immersed in an HF aqueous solution, metals and organic substances penetrating during formation of the texture by anisotropic etching are removed together with the oxide film
Data Source
AI summary
The method for manufacturing a crystalline silicon substrate for a solar cell includes: forming a texture on the surface of a single-crystalline silicon substrate by bringing an alkali solution and the surface of the single-crystalline silicon substrate into contact with each other; bringing an acidic solution and the surface of the single-crystalline silicon substrate into contact with each other to perform an acid treatment thereon; and then by bringing ozone water and the surface of the single-crystalline silicon substrate into contact with each other to perform an ozone treatment thereon. One aspect of embodiment is that the acidic solution used for the acid treatment is hydrochloric acid. Another aspect of embodiment is that the ozone treatment is performed by immersing the single-crystalline silicon substrate into the ozone water bath.