AlCl3 treatment: Tailoring band alignment and enhancing performance for Cu2Cd0.4Zn0.6SnS4 solar cells

Abstract

In this study, we proposed a low-cost and non-toxic AlCl3 solution treatment for tailoring the band alignment to passivate the defects at grain boundaries (GBs) of Cu2Cd0.4Zn0.6SnS4 (CCZTS) solar cells. With the treatment, much reduced leakage currents at GBs of the CCZTS film were demonstrated through CP-AFM measurements. In addition, we found the conduction band offset turns from downward to upward and valance band offset turns from upward to downward after the treatment. This type of band alignment can deplete both electron and hole and reduce the recombination at GBs, which is responsible for the reduced leakage current at GBs. Consequently, the CCZTS solar cell performance was improved with fill factor from 65% up to 71% and efficiency up to 11.10%. Our work not only provides a new and effective passivation method for high efficiency CCZTS solar cells, but also demonstrates a new direction for optimizing the solar cells performance with band alignment engineering.