Fig. 7. Proposed nanoscale formation mechanism for CZTS nanoparticles annealed with and without K. Without K, individual particles cannot be merged completely, and the film remains porous and small-grained. With K, a liquid phase in the form of K2Sx or similar could be formed, and it will assist the sintering of the particles. The final film will thus become more dense and with larger grains. Sketch inspired by Tiong et al.6.
