Nature Materials, Published online: 03 August 2026; doi:10.1038/s41563-026-02703-6Challenges in the preparation of uniform large-area kesterite Cu2ZnSn(S,Se)4 (CZTSSe) thin films have hindered the scalability of related solar cells. A molecular-level regulation of metal–organic coordination achieves uniform selenization and crystallization, allowing formation of homogeneous CZTSSe thin films over 10 cm2, leading to efficient kesterite solar cells and modules.