Order-disorder related band gap changes in Cu2ZnSn(S,Se)4: Impact on solar cell performance

We investigate the impact of order-disorder related band gap changes on finished Cu₂ZnSn(S,Se)₄ solar cells. Solution-processed solar cells are post-annealed in a tube furnace in order to modify the Cu-Zn disorder within the kesterite unit cell. A decrease in this disorder leads to an increased band gap of the absorber. The latter is detected using electroreflectance spectroscopy. In our experiments the change in the open-circuit voltage follows the change in the absorber band gap. However, the open-circuit voltage deficit of the solar cell remains unaltered. Still, power conversion efficiencies could be increased by 1%, mainly due to an increased open-circuit voltage.