Fabrication of Cu2ZnSn(S,Se)4 photovoltaic devices with 10% efficiency by optimizing the annealing temperature of precursor filmsElectronic supplementary information (ESI) available. See DOI: 10.1039/c7ra13069d

The annealing temperature of solution-processed Cu 2 ZnSn(S,Se) 4 (CZTSSe) precursor films has been carefully optimized for favorable selenization. At higher temperature, more solvent will be removed, and the crystallinity of the precursor films can be improved. It is found that, although the crystallinity of selenized film is continuously enhanced by increasing the temperature, a dense CZTSSe film with round and large grains can only be achieved at medium high temperature ranging from 350 to 400 °C. Further investigation reveals that, in this regime, the carrier and defect densities are obviously reduced, leading to average photoelectric conversion efficiency (PCE) improved from 5.1% to 9.4%. An optimal annealing temperature of 380 °C is obtained and up to 10.04% of photoelectric conversion efficiency has been achieved. Fabrication of a champion solar cell with 10.04% efficiency by optimizing the annealing temperature of precursor films.