Elucidating the role of TiCl4post-treatment on percolation of TiO2electron transport layer in perovskite solar cells

The ideal electron transport layer of a high performance perovskite solar cell should have good optical transparency, high electron mobility, and an energy level alignment well-matched with the perovskite material. In this work, we investigate the role of TiCl(4)post-treatment of the mesoporous TiO(2)electron transport layer by varying the concentration of TiCl(4)and characterizing optical and electrical properties, charge carrier dynamics, and photovoltaic performance of mesoscopic CH(3)NH(3)PbI(3)solar cells. It is found that the TiCl(4)treatment provides an additional interconnection between the TiO(2)particles, leading to better percolation as evident from high resolution cross-section images and chemical maps. This enhances effective electron mobility in the material as well as significantly reduces average sub-bandgap absorption due to defects and electronic disorder determined by photothermal deflection spectroscopy. Moreover, improvement of interfacial contact due to a smoother surface contributes to more efficient charge extraction and suppressed charge recombination and reduced hysteresis. As a result, the optimized device based on TiCl(4)post-treated mesoporous TiO(2)achieved the highest conversion efficiency of 17.4% compared with 14.1% for the device with pristine mesoporous TiO2.