Effect of surface modification via sol-gel spin coating of ZnO nanoparticles on the performance of WO 3 photoanode based dye sensitized solar cells

In this paper, we have reported the improvement of electro-optical performance of dye sensitized solar cells based on highly porous WO3 nanoparticles as photoanode by an ultrathin coating of ZnO nanoparticles with varying precursor solution concentration over WO3 surface and the results were compared with the performance of a Dye Sensitized Solar Cell (DSSC) fabricated with bare WO3 photoanode. The semiconducting material WO3 was chosen in search of a photoanode material for DSSC alternative to TiO2. But the performance of pure WO3 based DSSC was found to be extremely poor in spite of having several advantageous properties. To improve the photovoltaic performance, we have coated the WO3 surface with varying concentrations of the ZnO precursor solution. It was observed that the concentration of the precursor solution of ZnO highly controls the performance of the DSSC. From the electrochemical measurements, it was found that the bare WO3 cell suffers high electron recombination. But the coating of an ultrathin layer of ZnO over the WO3 surface introduces an energy barrier and reduces the electron recombination and thereby enhances the cell performance. The solar cell energy conversion efficiency was found to be highest for 5 mM ZnO precursor solution concentration and it decreases with the increase in concentration further and becomes very low at a concentration of 25 mM. This may be attributed to the poor dye adsorption on the WO3 surface due to complete screening by the thicker ZnO layer. © 2020 Elsevier GmbH