Comparison of chalcopyrite and kesterite thin-film solar cells

The CZTS-based absorber layer exhibits lower current characteristics than the CIGSe-based absorber layer in terms of the band gap alignment and electron-hole recombination at the CdS-absorber layer interface. Moreover, we demonstrate that defects are one of the causes of the voltage loss. The defects caused by secondary phases inside the CZTS-based absorber layer exhibit a deep energy level inside the band gap and act as electron-hole recombination centers and strong electron-trapping centers. Therefore, in order to improve the efficiency of CZTS-based thin-film solar cells, it is important to control the band gap alignment at the CdS-absorber layer interface and to suppress the formation of secondary phases inside the absorber.