Impact of the degree of Cu-Zn order in Cu2ZnSn(S,Se)4 solar cell absorbers on defect states and band tails
M. Lang, T. Renz, A. Opolka, C. Zimmermann, C. Krämmer, M. Neuwirth, H. Kalt, and M. Hetterich
Appl. Phys. Lett. 113, 033901 (2018)
In order to identify the impact of the degree of Cu–Zn order in kesterite Cu2ZnSn(S,Se)4 solar cell absorbers on defect states and band tails, we perform photoluminescence (PL), photoluminescence excitation, and time-resolved photoluminescence (TRPL) spectroscopy. The PL lineshape and further PL characteristics such as state filling are analysed as a function of Cu–Zn order. Furthermore, TRPL decays and band tails are quantified. No significant modification in the defect states is caused by changes in Cu–Zn order, meaning that the formation of the defect states is not mainly determined by disorder in the Cu–Zn plane. In regard to band tailing, a small tendency to a decrease in the tailing parameter for the states with a high degree of Cu–Zn order compared to states with a low degree of Cu–Zn order is obvious. However, this reduction is small compared to the reduction of the defect density accompanied by the increase in the degree of Cu–Zn order. Hence, band tails are not mainly formed due to disorder in the Cu–Zn planes.