Charge Transport Characteristics of High Efficiency Dye-Sensitized Solar Cells Based on Electrospun TiO2 Nanorod Photoelectrodes

Abstract

In this report, dye-sensitized solar cells (DSSCs) with high energy conversion efficiencies were fabricated using TiO2 nanorods electrospun from a solution mixture of titanium n-propoxide and poly(vinyl acetate) in dimethyl formamide. Investigation of the charge transport characteristics of this unique type of DSSC disclosed that the efficiency of the DSSCs was enhanced by optimizing the nanorod morphology to facilitate charge transport. Our TiO2 nanorods have an intrinsically higher sensitizer loading capability than conventional TiO2 nanoparticles and have much slower recombination lifetimes compared to conventional nanoparticles. Long electron lifetime in nanorod electrode contributes to the enhanced effective photocarrier collection as well as the conversion efficiency. The electron transport behavior of nanorod photoelectrodes was further improved by TiCl4 post-treatment. The post-treatment reduces the pore volume of nanorod photoelectrodes while improving inter-rod connectivity and enhancing electron diffusion. The electron diffusion coefficient of post-treated nanorod was ∼51% higher than that of an untreated one, leading to a charge collection efficiency that was 19% higher at a incident photonflux of 8.1 × 1016 cm−2 s−1. Finally, the efficiency of nanorod-based DSSCs was optimized at a photoelectrode thickness of 14 μm to achieve 9.52% under masked illumination of simulated solar light, AM 1.5 Global (Voc = 761 mV, Jsc = 17.6 mA cm−2, fill factor = 70.0%).