Effect of aspect ratio of c-axis oriented ZnO nanorods on photoelectrochemical performance and photoconversion efficiency

Abstract In recent times, the field of dye-sensitised solar cells (DSSC) has made great strides; but has yet to achieve high efficiency with existing photoanode material.To achieve this goal, materials are required that have structural superiority.Tuning the morphology of metal oxide nanomaterials has become one of the most emerging techniques to improve the performance of the photoanode for dye sensitised solar cells (DSSC) application. The diverse morphologies of ZnO based photoanode allow achieving superior photoconversion efficiency in DSSC. Thus, the present study reports the synthesis of ZnO nanorods using microwave technique with various aspect ratios and its utilisation as photoanode for DSSC by changing the microwave power alone. More importantly, the microwave synthesis route has advantages over the conventional synthesis methods in terms of duration of the reaction and uniformity of the nanostructures. The structural and morphological analysis of the samples confirms the formation of nanorods with a preferential growth along the c-axis, which is further assembled to form a flower like structure. Lower microwave irradiation favours the formation of nanorods with a higher aspect ratio due to the variation in axial and lateral growth of ZnO. Among all the samples, the ZnO nanorod with the highest aspect ratio exhibits improved photoconversion efficiency compared to the remaining samples. The photoconversion efficiency of the ZnO photoanode with the highest aspect ratio was found to be 2.5 times greater than that of the lowest aspect ratio. This is explained further based on detailed physicochemical and photoelectrochemical (PEC) analyses, which helps establish the correlation between the charge carrier dynamics and the dye adsorption capacity of the optimal photoanode.