Optimizing zinc oxide nanorods based DSSC employing different growth conditions and SnO coating

Abstract

Effect of seed layer thickness, growth time and tin oxide coating was studied for optimized performance in ZnO nanorods (NRs) based Dye-sensitized solar cells (DSSCs). Three different seed layer thickness of 150 nm, 250 nm and 350 nm were used for hydrothermal growth of ZnO NRs varying the growth time from 12 to 20 h. Among all devices, cell fabricated employing ZnO NRs grown for 20 h using 150 nm thick seed layer yielded the highest power conversion efficiency (PCE) of 0.25%, with a short circuit current density (Jsc) of 1.549 mA/cm2, open circuit voltage (Voc) of 0.5 V and a fill factor of 32.68. A significant increase in short circuit current density was observed by employing tin oxide coating on zinc oxide nanorods based DSSCs compared to simple ZnO based DSSCs. This increase of Jsc is attributed to better electron transfer, increased dye loading, more charge carriers generation and lower recombination of charge carriers. The DSSC fabricated with SnO coated ZnO NRs also showed an increase in open circuit voltage and fill factor because of the higher conduction band edge of SnO as compared to ZnO. A maximum efficiency of 0.81% was achieved when seed layer thickness was kept at 150 nm, hydrothermal growth of ZnO NRs was continued for 20 h, and 2 h of SnO coating was performed followed by 350 °C annealing. An increase of 224%, 61.39% and 38% was observed for PCE, short circuit current density (Jsc) and open circuit voltage (Voc) respectively, compared to the device fabricated without SnO coating of ZnO NRs with the same seed layer thickness and growth time. Scanning electron microscopy was performed to visualize and understand function of tin oxide coating on zinc oxide nanorods used in dye-sensitized solar cell.