Oriented nanocrystalline silicon oxide contact enables excellent passivation for silicon solar cells

What is it about?

We provide a novel and effective solution. Using the c-Si substrate as a template and the hydrolysis-condensation chain reaction of tetraethoxysilane (TEOS), the highly crystalline and vertically oriented SiOx (v-SiOx) tunnel passivated contact was grown on the c-Si wafers, forming high crystallinity, few grain boundaries, and few defects in the vertical direction. Ultimately, we found that the TOPCon cells with the v-SiOx polycrystalline tunnel contacts exhibit higher charge mobility and effective excess carrier lifetime compared to conventional a-SiOx:H, improving the overall cell performance. We achieved an open-circuit voltage of 746 mV and a short-circuit current density of 41.54 mA cm⁻², resulting in the first commercially available TOPCon solar cell with a power conversion efficiency (PCE) exceeding 26.01%.

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Photo by American Public Power Association on Unsplash

Photo by American Public Power Association on Unsplash

Why is it important?

The tunnel oxide passivated contact (TOPCon) technology is a solar cell technology based on the principle of selective carriers, which is the third generation of solar cell technology following the back surface field (BSF) technology and the passivated emitter and rear contact (PERC) technology. By inserting an ultrathin layer of SiOx (1~2 nm) between c-Si and the emitter, effectively reducing surface remombination and metal contact remombination. We have demonstrated the importance of the SiOx passivated contact in our work earlier this year (Nature, 2024, 626, 105-110). However, the commonly used ultrathin tunnel oxide contacts are hydrogenated amorphous SiOx (a-SiOx:H) nanolayers prepared by chemical vapor deposition (CVD), resulting in problems such as porousness, defects, and low charge mobility that cannot be solved yet. Therefore, optimizing the semiconductor physical properties of the SiOx tunnel contacts is the key to improve the TOPCon cells.

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