Charge transfer mechanism of AZO-ZnO photoanode based on impedance study for solar cell application

•Studied the effect of growth temperature on the length and defect of ZnO NR.•Charge transfer mechanism of NRs was investigated using electrochemical analysis.•Obtained current density of 0.82 mA/cm2 and photoconversion efficiency of 0.53 %.•Working mechanism of the NR-based cell was explained using a band diagram. Charge transfer mechanism in ZnO nanorods grown on aluminium doped zinc oxide substrates using a single step hydrothermal method was investigated as a function of ZnO nanorod (NR) growth temperature/nanorod’s length. Band-to-band transition and the defect state transition in the prepared nanorods was confirmed using photoluminescence spectroscopy. The increase in active sites up to an optimum growth temperature/nanorod’s length results in an increase of current density and photoconversion efficiency of the prepared NR. But with the further increase in the latter, the current density decreases due to the recombination of electrons. Nanorod grown at the optimized condition exhibited a current density of 0.82 mA/cm2 and a photoconversion efficiency η of 0.53 %. Electrochemical impedance spectroscopy and open-circuit photovoltage decay (OCPVD) measurement were employed to determine the charge transfer resistance Rct, double layer capacitance (Cdl) and the recombination time τ of zinc oxide nanorods of various length. The nanorod prepared at the optimized condition of 140 °C having an average length of 2.4 μm had superior current density and the better charge transfer mechanism. The study confirmed that this was due to the low charge transfer resistance Rct=1300Ω value and better recombination time τ=2.38s for the sample, which makes ZnO nanorods a promising candidate to be used as a photoanode in quantum dot sensitized solar cells.