Understanding Hysteresis Behavior in SnO2 Nanofiber-Based Dye-Sensitized Solar Cell

Abstract

Tin oxide (SnO2) nanofiber-based dye-sensitized solar cell (DSSC) exhibits an anomalous hysteresis effect on its current–voltage characteristics. While the one-dimensional nature of SnO2 nanofibers is considered facilitating effective charge transport in DSSCs, the surface states present in the SnO2 bandgap are observed to be playing an influential role in trapping and detrapping of charge carriers in the bulk as confirmed by electrochemical impedance spectroscopic studies. Forward and backward electrical bias sweeps identify the hysteresis effect in the performance of resulting DSSCs due to which 43% difference was observed in the photovoltaic performance. Charge carriers generated in the dye utilize the SnO2 nanofiber as a transport medium to reach electrode through energetically active SnO2 surface states which effectively trap and detrap the photogenerated charges during the transport resulting in the hysteresis effect. The observed hysteresis effect varies the maximum power density ( P ${}_{\rm MAX}$ ) and fill factor (FF) of the resulting DSSC by 35% and 25%, respectively, between forward and backward scans. The significant change in P ${}_{\rm MAX}$ and FF asserts that trapping and detrapping mediated charge transport process contributed to the variation in overall performance by 43%.