A Universal and Facile Method of Tailoring the Thickness of Mo(Sx,Se1-x)2, Contributing to Highly Efficient Flexible Cu2ZnSn(S,Se)4 Solar Cells

Flexible Cu2ZnSn(S,Se)(4) (CZTSSe) solar cells have attracted considerable attention due to their potential application in specific areas such as power sources for wearable electronics. However, the over-thick Mo(S-x,Se1-x)(2) at the back contact is one of the factors that limit the device performance. Herein, a facile strategy to inhibit the thick Mo(S-x,Se1-x)(2) layer by adding a proper proportion of sulfur during selenization is reported. It is found that the thickness of Mo(S-x,Se1-x)(2) can be effectively tailored via tuning the proportion of S, enabling a substantial decrease in series resistance. The suppression mechanism is mainly ascribed to the change of orientation of Mo(S-x,Se1-x)(2) induced by S, which limits the diffusion of Se to Mo. Accordingly, the total area efficiency of the flexible CZTSSe device improves significantly from 5.5 to 8.9% with the addition of 2% S, followed by a drop with more S. Furthermore, it is demonstrated that this strategy can also be applied to both kesterite and chalcogenide absorbers deposited on rigid Mo substrates to suppress the thick Mo(S-x,Se1-x)(2) layer, indicating the universality of this method. Overall, this work provides a general, facile, and effective approach to modify the back contact interface without introducing extra blocking layers.