Hole selective WOx and V2Ox contacts using solution process for silicon solar cells application

Abstract

We have prepared solution processed V2Ox and WOx (s-V2Ox and s-WOx) thin films as hole selective contacts for Si solar cell applications. The material properties of s-V2Ox and s-WOx thin films were investigated to shed light on their performance as selective contacts, and their hole selectivity on Si were also characterized. It is found that there is a larger density of oxygen vacancies in s-V2Ox than s-WOx resulting in a larger amount of gap states, but their energy levels in s-V2Ox might not be favourable for carrier transport. We have measured a high work function of 5.17 eV for s-V2Ox and the Fermi level is located above the conduction band suggesting its n-type characteristic. On the other hand, the work function of s-WOx is only 4.71 eV and it is also a n-type semiconductor with the Fermi level situated below the conduction band. From the carrier lifetime studies, both materials are found to exhibit moderate passivation effect on Si and overall they can serve as good hole selective contacts for Si. The optimized power conversion efficiencies of planar s-V2Ox/Si and s-WOx/Si heterojunction solar cells are 10.8% and 9.3% respectively. To the best of our knowledge, the performance of the planar s-V2Ox/Si HSC is better than other reported result for planar configuration using solution process, and this is the first time that the performance of the planar s-WOx/Si HSC is reported.