Preparation of high-quality Cu2ZnSnS4 thin films for solar cells via the improvement of sulfur partial pressure using a static annealing sulfurization approach

Abstract

Cu2ZnSnS4 (CZTS) thin films were prepared by spin-coating deposition of sol–gel precursor followed by sulfurization in sulfur atmosphere. A comparative study on the properties of the CZTS thin films sulfurized by using dynamic annealing and static annealing approaches was carried out. A higher sulfur partial pressure processed from static annealing was demonstrated. Static annealing contributed to the reduction of Sn loss. The CZTS thin films sulfurized by static annealing showed larger grains, better crystallinity and thinner MoS2 layer, but more ZnS on surface and minor Cu2−xS, SnS2 and SnS at the back surface. Diffusion of Zn into MoS2 layer was found to be associated with those minor secondary phases at the back surface. Solar cells incorporating the CZTS thin films sulfurized by static annealing exhibited a better cell performance with the device efficiency as high as 6.15%, which was further improved to 6.68% by using hydrochloric acid solution to etch ZnS at the surface and inhibiting the decomposition reaction of CZTS at the back surface based on the use of a thin ZnO nanolayer barrier.