Interface‐Engineered Band Alignment and Defect Passivation Enabling 13.64% Efficient Inkjet‐Printed CZTSSe Solar Cells

Abstract Inkjet‐printed Cu 2 ZnSn(S,Se) 4 (CZTSSe) has emerged as a promising route for cost‐effective and high‐throughput production of photovoltaic devices. To further enhance the performance of CZTSSe solar cells, it is urgently necessary to address the issues of severe interface recombination and carrier transport resistance within the devices. In this sense, a surface modification strategy is introduced by treating the inkjet‐printed CZTSSe absorber surface with cadmium chloride (CdCl 2 ). As a result, the Cd‐treated CZTSSe films exhibit smooth and compact surfaces and a small conduction band offset, which boosts carrier transport. Furthermore, the Cd treatment significantly reduces interface defects from 5.1 × 10 15 to 2.4 × 10 15 cm −3 , thereby reducing carrier recombination while expanding the depletion width from 138 to 272 nm and improving carrier collection efficiency. Consequently, the optimized CZTSSe device achieves a stimulating increase in power conversion efficiency from 11.83% to 13.64%, which is the highest efficiency reported to date for inkjet‐printed CZTSSe solar cells. This work provides critical insights for advancing cost‐effective and high‐performance inkjet‐printed CZTSSe solar cells.