Solution-processed kesterite solar module with 10.1% certified efficiency

Solution processing has great advantages for emerging thin-film solar cells but remains a big challenge for multielemental inorganic films due to complicated phase evolution and grain growth during crystallization. Here we report the fabrication of uniform, large-area Cu₂ZnSn(S,Se)₄ (CZTSSe) films and solar modules from solution. By tuning the thiourea/metal ratio to increase film porosity—thereby promoting more uniform vertical reaction and lateral grain growth—we improved the uniformity of CZTSSe films and achieved a single-cell efficiency of 13.4% and a solar module efficiency of 8.91%. We further optimized the module structure to reduce non-ideal contact and patterning-induced shunt and resistive losses, resulting in a champion CZTSSe module with a National Renewable Energy Laboratory-certified efficiency of 10.1%. This module also exhibits the lowest cell-to-module loss in open circuit voltage and current density among state-of-the-art emerging thin-film solar modules. Our work demonstrates the viability of solution processing to deposit uniform, large-area CZTSSe film and efficient solar modules, advancing the development of the technology.