Morphological variations of ZnO nanostructures and its influence on the photovoltaic performance when used as photoanodes in dye sensitized solar cells

Different hierarchical architectures of ZnO were synthesized via optimization of ethylenediamine (EDA) concentration in a simple low-temperature hydrothermal route and their various photoanode characteristics are effectively used in superior DSSC performance. In a sequence of morphological changes from the nanoparticles to nanorods and the nanoflowers structures, gradually and systematically, the zinc-interstitial and oxygen-vacancy related phases reduce, bandgap redshifts relative to its bulk structure, surface area increases and the dye-loading capacity improves. In photoanodes with ZnO nanoflower structures, the incident photon-to-current conversion efficiency gradually increases to ∼46.6% via significant photo-absorption by a larger number of dye-molecules adsorbed on its enhanced specific surface area and via its high dye-loading capacity that facilitate an amplified photogeneration of electrons upon light-exposure on the DSSC. Furthermore, the lowest charge transfer resistance and hence an improved charge transport pathway prevailing in the device consequences superior photovoltaic conversion efficiency (η) of the DSSCs, which gradually advances to ∼4.42%, via increasing the short-circuit current density (JSC) to ∼10.75 mA cm−2 and the open-circuit voltage (VOC) to 0.73 V. Morphological changes in the ZnO nanostructures are demonstrated to significantly influence the photovoltaic performance when used as an effective photoanode of the DSSCs, which has never been reported earlier.