Influences of Extended Selenization on Cu2ZnSnSe4 Solar Cells Prepared from Quaternary Nanocrystal Ink

Kesterite Cu 2 ZnSnSe 4 (CZTSe) thin films prepared by the selenization of mechanochemically synthesized Cu 2 ZnSnS 4 (CZTS) nanocrystal films are systematically investigated as a function of the annealing time in terms of the phase purity, microstructure, composition, and device characteristics. It is shown that selenization for an extended time does not cause a noticeable amount of Sn loss or segregation of Zn-rich layers. Thus, the prolonged annealing leads to improvements (reduction) in the shunt conductance, reverse saturation current, and diode ideality factor. However, it also leads to a deterioration of the series resistance, of which influence turned out to overwhelm all of the aforementioned positive effects on the device performance. As a consequence, the CZTSe solar cell exhibits its highest efficiency (5.43%) at the shortest annealing time (10 min). Impedance spectroscopy is…