Optimization of tunnel junction IBC solar cells based on a series resistance model

Abstract

This work presents the upscaling of the tunnel IBC technology on large area, Czochralski (Cz) n-type wafers. At the junction level, a self-aligned PECVD masking technology has been developed for the deposition of hydrogenated nano-crystalline silicon (nc-Si:H) layers on industrial 6-inch pseudo-square wafers. This damage free patterning technology allows state-of-the-art passivation with a minority carrier lifetime of 9 ms at an injection level of 10(15)cm(2), thus enabling extremely long diffusion lengths up to several millimetres. The use of indiumfree, cost effective aluminium-doped zinc oxide strongly reduces the materials bill of the tunnel-IBC technology while maintaining very low contact resistance for both the electron and the hole contacts. Remarkably, these tunnel-IBC devices demonstrated a conversion efficiency of 25% on large area (90.25 cm(2)) industrial wafer with a thickness of 155 mu m. Series resistance analysis points out probable losses from the hole contact and the base. The limitation of the Transfer Length Method is discussed when used to extract the hole contact resistance.