Boosting Kesterite Solar Cell Performance with Tantalum Oxide Passivation Layer and In Situ Formed Point Contacts

Kesterite solar cells often suffer from low open‐circuit voltage due to interface recombination. To address this, a passivation approach is explored using a dielectric layer between the absorber and buffer layer, coupled with a point contact structure. In this method, carrier transport is enabled through point contacts while effectively passivating regions covered by oxide. In this study, although forming point contacts on the front surface poses processing challenges, a novel solution is presented. Herein, in situ formed ZnS nanoparticles (NPs) during Cu 2 ZnSn(S, Se) 4 (CZTSSe) absorber fabrication is utilized as a nanomask for front surface point contacts. A thin TaO x layer, acting as the passivation layer, is deposited over the CZTSSe surface with ZnS NPs by using atomic layer deposition (ALD). The selective removal of these NPs by deionized water soaking creates size‐controlled point contacts without damaging the absorber surface. In this approach, the first successful implementation of TaO x in enhancing CZTSSe solar cell efficiency, which jumps from 6.17% to 9.02% due to this strategy, is marked. The passivation mechanism involves sodium attraction during ALD, reduced interface defects, and the generation of positive fixed oxide charges. In this innovative method, not only solar cell efficiency is improved but new insights are also provided into using secondary phases as nanomasks in interface engineering.