Promoting carrier collection by DMF/DMSO binary solvent for efficient kesterite solar cells

Photo-generated carrier recombination loss and transport are the key issues affecting the photovoltaic performance of kesterite solar cells. Here, through a binary solvent engineering of dimethylformamide (DMF)/dimethyl sulfoxide (DMSO) in the precursor solution, over 12% efficient Cu2ZnSn(S,Se)4 (CZTSSe) solar cells are fabricated with outstanding carrier collection. It is found that a more Cu-poor and rough film surface is formed when DMSO is partially replaced by the DMF solvent, resulting in solar cells with enhanced short-wave absorption and improved short-circuit current density. Carrier recombination and band alignment analysis show that the increased depletion width, built-in voltage, and reduced conduction band offset improve carrier separation and transport. This work provides an intrinsic origin for the performance improvement of binary solvent-engineered CZTSSe solar cells and a simple and effective method for fabricating high-performance kesterite photovoltaics.