DMF‐Based Large‐Grain Spanning Cu(2)ZnSn(S (x) ,Se(1‐) (x) )(4) Device with a PCE of 11.76%

A main concern of the promising DMF‐based Cu(2)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 Cu(2+) plus Sn(2+) 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.