Improving photovoltaic properties of ZTO-based DSSCs using surface modification of Zn2SnO4 nanoparticles prepared by co-precipitation method

Abstract We synthesized high-quality Zn2SnO4 nanoparticles via simple co-precipitation method and crystallinity along with phase purity of resultant nanopowders were increased by applying different values of pH, precursor concentrations, and annealing temperatures. After that, the crystalline Zn2SnO4 nanoparticles with an average size of about 35 nm were used as a mesoporous layer and then modified by using MgO and Al2O3 passivation layers. We optimized the thickness of these barrier layers with controlling the concentration of solution and velocity of the spin-coating process which had a vital role in suppressing recombination and significantly enhanced performance of DSSCs. The highest electronic parameters of JSC=8.59 mA/cm2, VOC=0.66 V, and FF=0.51 were obtained for the MgO-treated device (with rotation speed of 4000 rpm) that showed 40% increment in the efficiency from 2.07% to 2.90% compared to the untreated sample. The improvement of VOC was observed in all treated samples that attribute to an upward shift of the Zn2SnO4 flat band energy and could be explained by the blocking effect of the interfacial layer. Further investigation through the transport and recombination mechanisms were carried out by electrochemical impedance spectroscopy, open-circuit voltage decay, and dye-loading process, which confirmed faster transport rate and slower electron recombination in the most modified devices.