The role of back contact patterning on stability and performance of Si IBC heterojunction solar cells

Interdigitated back contact (IBC) Si heterojunction solar cell initial performance and stability over time exhibits a critical dependence on the patterning processes, especially in defining the gap structure between emitter and base contacts. Patterning processes using photoresist can result in degradation even with dark storage in a dry environment over days, while other processes using a-SiN_X:H for patterning yield stable devices over months. Use of photoresist (PR) as a mask in PECVD to form interdigitated contacts results in a gap that is insufficiently passivated and leads to cell degradation. Use of a-SiN_X:H as a mask creates a multi-layer gap structure which improves the cell performance and stability. The laser fired base contact (LFC) reduces V_OC slightly due to increased recombination loss, but does not cause additional instability. A stable efficiency of 17.9% was achieved in an IBC-Si heterojunction solar cell using all low temperature processes that incorporated a multi-layer gap passivation structure.