DMF‐Based Large‐Grain Spanning Cu2ZnSn(Sx,Se1‐x)4 Device with a PCE of 11.76

A main concern of the promising DMF‐based Cu2ZnSn(Sx,Se1‐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 (Voc) 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 Voc (>500 mV) and PCE of 11.76%, which are both the maximum values among DMF‐based solar cells at the current stage. Cu2ZnSn(Sx,Se1‐x)4(CZTSSe) films with large‐grain spanning structures are achieved by taking advantage of the synergistic optimization with a Cu2+ plus Sn2+ redox system and optimal pre‐annealing temperature of 430 ℃. A high open‐circuit voltage (Voc) (>500 mV) and a power conversion efficiency (PCE) of 11.76% in the champion device are both the highest values of DMF‐based CZTSSe devices at present.