Optimization of PECVD–ONO rear surface passivation layer through improved electrical property and thermal stability

Abstract The surface passivation is one of the crucial steps to achieve high conversion efficiencies in c-Si solar cells. Though thermal silicon oxide (SiO 2 ) and silicon nitride (SiN x ) provides a good passivation layer the high temperature process of SiO 2 and the fixed positive charge of SiN x on p-substrate cause detrimental effect in surface passivation. A thermally stable thin film with a negative charge (for p-substrate) passivation layer is required to develop a good rear passivation suitable for PERC cells processed with screen printing. In this paper, a PECVD stack layer system consisting of SiO x , SiN x , and SiO x was employed for rear side passivation. The optimal refractive index of silicon oxide and silicon nitride thin film was found by varying the silane, ammonia and nitrous oxide gas ratios. A low surface recombination velocity (SRV) was achieved using interface treatment. Carrier lifetime of 212 μs and interface trap density of 8.265 × 10 9  cm −2  eV −1 was obtained. With optimized PECVD–ONO layer, the solar cell parameters measured were V OC of 647 mV and efficiency of 19.3%, while those of the reference solar cell were V OC of 621 mV and efficiency of 18.6%.