Influence of order-disorder in Cu2ZnSnS4 powders on the performance of monograin layer solar cells

In this study the influence of low-temperature structural ordering in absorber material to the performance of Cu2ZnSnS4 (CZTS) monograin layer (MGL) solar cells was investigated. The shift of peak position in low temperature and room temperature photoluminescence measurements was used to estimate the Cu-Zn disorder level in CZTS monograin powders. The degree of Cu-Zn ordering was changed by using different cooling times after annealing CZTS powders in S atmosphere at 740 °C and by additional annealing at temperatures below critical temperature (Tc ~ 260 °C) for different time periods. Current-voltage measurements revealed that the low-temperature thermal treatments resulting in increased ordering of CZTS absorber material had significant impact on the MGL solar cell characteristics, mostly, the values of open circuit voltage (Voc) were increased. The highest Voc of 784 mV was measured for the solar cell based on the powder that was cooled from 740 °C to room temperature for 5 min followed by annealing at 150 °C for 24 h. Optimal conditions for low-temperature annealing to improve CZTS MGL solar cells' performance were found to be 4 h at 150 °C. These improvements resulted in CZTS MGL solar cell power conversion efficiency of 9.1% (active area).