Hydrothermal growth optimization of vertically aligned ZnO nanowire arrays and their dye-sensitized solar cell performance under air/oxygen environments

Abstract

In this work, the hydrothermal growth parameters of vertically aligned ZnO nanowire arrays on FTO substrates were optimized for best surface coverage and minimal stacking and entanglement between nanowires for dye-sensitized solar cell (DSSC) application. The concentration of seed layer solution was found to be essential in reducing the stacking effect of adjacent nanowires. The growth temperature study has revealed a remarkable existence of a temperature window in the range 90 C-110 C, beyond which the nanowire lengths start to decline. We attributed the nanowire length regression above 110 C to the enhanced homogeneous nucleations in the growth solution. Nanowire entanglement started to be observable at ~100 C for a growth duration of 2 h. DSSCs were fabricated using the grown ZnO nanowire arrays that are post-annealed under air and pure oxygen gas environments. Oxygen post-annealing resulted in a remarkable decrease in the open circuit voltage (VOC), which we attributed to the large impact of band bending.