Tailoring band alignment of Cu2ZnSn(S,Se)4/CdS interface by Al2O3 drives solar cell efficiency

Abstract

The p/n heterojunction with low surface recombination losses and good band alignment is one of the key factors for obtaining efficient photovoltaic (PV) devices. Here, ultrathin Al2O3 is introduced, and the effects of its thickness and growth temperature on the PV performance of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells are investigated. The result indicates that the increased depletion width and built-in voltage after appropriate Al2O3 treatment promote the separation and transport of photogenerated carriers. The absorber surface composition and defect are optimized, and the interface band alignment is modified by reducing the conduction band offset successfully, which drives the carrier collection and increases open-circuit voltage by 60 mV. The dual passivation mechanism of chemical passivation and field-effect passivation is realized by introducing Al2O3 into kesterite solar cells. This work not only reveals the intrinsic mechanism for performance enhancement CZTSSe solar cells with Al2O3, but also provides a significant guidance for the band adjustment at the interface.