Textured Silicon Substrate Amorphous Crystalline Silicon Layer Fill Factor
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Solution Overview
Problem
Existing photovoltaic devices face a trade-off between optimizing fill factor (FF) and open-circuit voltage (Voc), as increasing the coverage of crystalline regions in amorphous silicon layers improves FF but reduces Voc, and vice versa.
Innovation Solution
A photovoltaic device with a silicon substrate having a textured surface featuring pyramids, where the amorphous silicon layer is amorphous in peak and slope portions and has crystalline regions growing perpendicularly from the substrate in valley portions, with higher coverage of crystalline regions in valley portions than amorphous regions, optimized through a fabrication method involving etching and surface treatment with hydrofluoric acid and hydrogen peroxide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the coverage of crystalline regions in the amorphous silicon layer is increased to improve fill factor, then the fill factor is improved, but the open-circuit voltage is reduced
Solution Approach 1:
The patent applies local quality by creating different regional characteristics within the amorphous silicon layer: valley portions have higher crystalline region coverage to improve conductivity and fill factor, while peak and slope portions maintain amorphous structure to preserve open-circuit voltage. This spatial differentiation of material properties resolves the contradiction between improving fill factor and maintaining open-circuit voltage.
2Reliability
If the coverage of amorphous regions in the amorphous silicon layer is increased to maintain open-circuit voltage, then the open-circuit voltage is maintained, but the fill factor is reduced
Solution Approach 1:
The patent maintains amorphous regions in peak and slope portions of the silicon substrate surface, which preserves open-circuit voltage while allowing crystalline regions to dominate in valley portions to maintain adequate fill factor. This localized distribution strategy resolves the contradiction between maintaining open-circuit voltage and preserving fill factor.
3Loss of energy
If a textured surface with pyramids is formed to reduce reflected light, then light absorption is improved, but the structural complexity is increased
Solution Approach 1:
The patent employs a pyramidal texture with curved surfaces on the silicon substrate to reduce light reflection. The curved geometry of the pyramids causes multiple internal reflections of incident light, increasing light absorption while the systematic arrangement maintains manufacturing feasibility through standard texturing processes.
Solution Approach 2:
The textured surface is segmented into distinct geometric regions (peak portions, slope portions, and valley portions) that exhibit different material phases (amorphous and crystalline). This segmentation allows each region to be optimized for its specific function while collectively reducing reflected light and improving overall device performance.
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 configuration reduces resistive losses, improves the fill factor, and inhibits the reduction of open-circuit voltage, enhancing the overall power generation efficiency of the photovoltaic device.
Implementation Method 1
surface treating the first major surface having the texture, by submerging the first major surface in a mixed solution of hydrofluoric acid and hydrogen peroxide
Implementation Method 2
forming, on the surface-treated first major surface, a first amorphous silicon layer having an uneven surface corresponding to the texture, by vapor deposition using a raw material gas containing silicon
Implementation Method 3
epitaxially-grown regions in valley portions of the amorphous silicon layer are greater in thickness than epitaxially-grown regions in portions other than the valley portions of the amorphous silicon layer
Data Source
AI summary
A photovoltaic device includes: a silicon substrate having a front surface having a texture; and an amorphous silicon layer having an uneven surface corresponding to the texture, wherein the amorphous silicon layer is amorphous in peak portions and slope portions extending between the peak portions and valley portions of the uneven surface, and has crystalline regions which grow, in a pillar manner, approximately perpendicularly from a substrate surface of the silicon substrate in the valley portions, the crystalline regions being discretely present along upper ends of the valley portions, the upper ends being opposite lower ends of the valley portions, the lower ends being in contact with the silicon substrate, wherein coverage of the crystalline regions in the valley portions is higher than coverage of amorphous regions in the valley portions.