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

• The effect of I amount on the photovoltaic performance was investigated.
• The enhancement in η of ZnO:I DSSCs was from 38% to 77% compared with ZnO DSSCs.
• Appropriate I doping enhanced light harness and inhibited charge recombination.

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 (η) of 3.6–4.6%. The enhancement in η of ZnO:I DSSCs is from 38% to 77% as compared to undoped ZnO DSSCs. The significantly enhanced η 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.

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