Vacancy-enhanced cation ordering via magnesium doping to enable kesterite solar cells with 14.9% certified efficiency

Atomic disorder is a widespread issue in multi-element crystalline materials and poses a critical challenge to the performance of Cu 2 ZnSn(S, Se) 4 (CZTSSe) photovoltaic devices. In particular, Cu–Zn disorder is prevalent in CZTSSe due to its low formation energy, leading to the formation of high-concentration deep defects and severe charge loss. The regulation of this disorder remains challenging because of the trade-off between the thermodynamics of the disorder–order phase transition and the kinetics of atom interchange. Here we introduce additional vacancy defects at the CZTSSe surface via magnesium doping to reduce the energy barrier for atom interchange. This vacancy-assisted approach enhances the kinetics of Cu–Zn ordering, thereby reducing charge loss in the device. As a result, we achieve a power conversion efficiency of 14.9% certified by the Chinese National PV Industry Measurement and Testing Center in CZTSSe solar cells, marking an advancement in the development of emerging inorganic thin-film photovoltaics.