Investigation of iodine dopant amount effects on dye-sensitized hierarchically structured ZnO solar cells

We prepare a series of iodine doped zinc oxide monodisperse aggregates (ZnO:I) with various iodine concentrations as the photoanodes of dye-sensitized solar cells (DSSCs) to study iodine dopant amount-dependent photovoltaic performance. The iodine-doped DSSCs achieve overall conversion efficiency (eta) of 3.6-4.6%. The enhancement in eta of ZnO:I DSSCs is from 38% to 77% as compared to undoped ZnO DSSCs. The significantly enhanced eta of DSSCs is found to be correlated with iodine dopant amount. The optimum iodine dopant amount is determined to be 2.3 wt% by X-ray photoelectron spectroscopy. Furthermore, the incident photon to current conversion efficiency and electrochemical impedance spectroscopy data reveal a systematic correlation between photovoltaic properties and the iodine dopant amount. The enhancement of open-circuit potential of ZnO:I cells is arising from negative shift of their flat-band potential, as demonstrated by Mott-Schottky measurement. (C) 2014 Elsevier Ltd. All rights reserved.