Transparent Conductive Oxide Sputtering Damage on Contact Passivation in Silicon Heterojunction Solar Cells with Hydrogenated Nanocrystalline Silicon

Abstract

Mitigating the adverse effect of transparent conductive oxide (TCO) sputtering on the passivation quality of the heterojunction contact is very critical for achieving high-efficiency silicon heterojunction (SHJ) solar cells. Herein, n-type ultra-thin (5 nm) nanocrystalline silicon (nc-Si:H) is utilized as a contact layer in rear-junction SHJ solar cells. It is revealed that the TCO sputtering damage on the contact layer is caused by the ion bombardment during the sputtering process and cannot be fully recovered by low-temperature annealing. A more severe passivation deterioration is observed for the devices with nc-Si:H(n) having a higher microstructure factor. This result is explained by an increased ion penetration depth in the porous nc-Si:H film. By applying denser nc-Si:H(n) in SHJ solar cells, the front silicon film stack shows more resilience to sputter damage, yielding a remarkable cell performance on the M2-size wafer with certificated power conversion efficiency (η) of 23.87%. The sputter damage on nc-Si:H by TCO in SHJ solar cells is explored in depth for the first time from the perspective of silicon thin films.