Device comparison of champion nanocrystal-ink based CZTSSe and CIGSSe solar cells: Capacitance spectroscopy

Capacitance spectroscopy has been used to compare charge carrier and defect properties of champion nanocrystal-ink based CZTSSe and CIGSSe solar cells, with efficiencies reported here at 9.2% and 14.2%, respectively. Differences in energy level, frequency/temperature response, and contributions to bulk conductivity have been identified for the different materials. Due to these differences, contributions to the free carrier density have been associated with a single defect for CIGSSe, while associated with two defects in CZTSSe. Additionally, carrier freeze-out out at low temperatures has been identified for both devices, contributing to increasing series resistance at low temperatures as determined from the bulk conductivity. In addition to differences in defect formation, CZTSSe has been characterized with a reduced Vbi when compared to CIGSSe.