Passivation effect of tunnel oxide grown by N2O plasma for c-Si solar cell applications

Abstract

Electron-hole pair (EHP) recombination is a decreasing factor of the efficiency in silicon solar cells. The passivation layer reduces recombination by removing dangling bonds which act as recombination centers. Usually, SiNx, SiOx, SiONx and AlOx layers are used as passivation layer in solar cell applications. Tunnel oxide layer is one of the main issues to achieve high-quality passivation using carrier-selectivity between the silicon wafer and poly-Si layer. In this work, ultra-thin tunnel oxide layer by plasma enhanced chemical vapor deposition using N2O plasma is deposited on both sides of the samples. The RF power and substrate temperature are varied. Then phosphorus doped Si layer is deposited. The optimized tunnel oxide layer has low Dit (5.3 × 1010 cm−2eV−1) and high passivation effect (τeff of 923 μs, iVoc of 739 mV) when deposited with RF power of 200 W and a substrate temperature of 400 °C. This optimized tunnel oxide passivation layer is applied to the n-type c-Si solar cell. The fabricated solar cell showed Jsc of 41.04 mA/cm2 and VOC of 644 mV. Compared to the cell with chemical oxide passivation, Jsc and Voc increased by 0.2 mA/cm2 and 11 mV which were also higher than the cell with SiNx passivation.