One-Diode Model Equivalent Circuit Analysis for ZnO Nanorod-Based Dye-Sensitized Solar Cells: Effects of Annealing and Active Area

Abstract

Electrical characteristics of 1-D zinc oxide (ZnO) nanorod-based dye-sensitized solar cells (DSSCs) were experimentally measured and followed by theoretical analysis using simple one-diode model. Defect sites (mostly oxygen vacancies) in ZnO are typically responsible for lower DSSC performance, which are removed by annealing the ZnO nanorods at high temperatures up to 450 °C. The DSSC performances with respect to the different annealing temperatures (250 °C, 350 °C, and 450°C) were determined by measuring their I-V characteristics at 1-sun irradiation (AM 1.5G). The variations in series and shunt resistances of DSSC were estimated by fitting the experimental I-V characteristics with the ideal I-V curve obtained from the one-diode equivalent model of the DSSC. By increasing annealing temperature, reduction in the series resistance Rs of the DSSCs with a subsequent increase in the shunt resistance Rsh was obtained. Annealing temperature of 350 °C was found to be optimum at which maximum DSSC performances with 1-cm2 cell active area showing minimum Rs (0.02 kΩ) with high Rsh (1.08 kΩ) values were observed. Reduction in the active area of the DSSCs from 1 to 0.25 cm2 and further to 0.1 cm2 demonstrated improved device performance with ~56% and ~24% enhancement in the fill factor and open-circuit voltage Voc, respectively, due to the reduced sheet resistance and lower recombination rate resulting low series resistance and high shunt resistance, respectively. At the optimum annealing temperature, maximum DSSC efficiency of 4.60% was obtained for the 0.1-cm2 cell active area.