DMF-Based Large-Grain Spanning Cu₂ ZnSn(S_x ,Se_{1- x} )₄ Device with a PCE of 11.76

A main concern of the promising DMF-based Cu₂ ZnSn(S_x ,Se_{1- x} )₄ (CZTSSe) solar cells lies in the absence of a large-grain spanning structure, which is a key factor for high open-circuit voltage (V_oc ) and power conversion efficiency (PCE). A new strategy to achieve CZTSSe large-grain spanning monolayer is proposed, by taking advantage of the synergistic optimization with a Cu²⁺ plus Sn²⁺ redox system and pre-annealing temperatures. A series of structural, morphological, electrical, and photoelectric characterizations are employed to study the effects of the pre-annealing temperatures on absorber qualities, and an optimized temperature of 430 ℃ is determined. The growth mechanism of the large-grain spanning monolayer and the effect of redox reaction rate are carefully investigated. Three types of absorber growth mechanisms and a concept of critical temperature are proposed. The devices based on this large-grain spanning monolayer suppress the recombination of carriers at crystal boundaries and interfaces. The champion device exhibits a high V_oc (>500 mV) and PCE of 11.76%, which are both the maximum values among DMF-based solar cells at the current stage.