Novel spherical TiO2 aggregates with diameter of 100 nm for efficient mesoscopic perovskite solar cells

Novel monodispersed spherical TiO2 aggregate with a diameter of 100 nm (SP100), which is the smallest TiO2 spheres (or beads) reported thus far, has been prepared by a controlled hydrolysis and hydrothermal reaction. The obtained SP100 is a highly porous structure with an internal pore size of 12 nm and a surface area of 112 m(2)/g, and is shown to be an ideal building block of mesoporous TiO2 layer for CH3NH3PbI3-based perovskite solar cells (PSCs). The optimized PSC employing SP100 exhibits photovoltaic conversion efficiency of 18.41% with J(SC) of 22.91 mA/cm(2), V-OC of 1,049 mV and FF of 0.759. Furthermore, fabricated PSCs exhibit reproducible PCE values with little hysteresis in their J-V curves. Time-resolved photoluminescence measurement indicates that the PSC with SP100 (PSC-SP100), compared to the devices with the nanoparticles of 30 nm or 50 nm size shows notably faster electron injection from CH3NH3PbI3 to TiO2 layer, resulting from the extended contact area between perovskite and mesoporous TiO2 layer. Pulsed light-induced transient measurement of the photocurrent indicates that PSC-SP100 shows significantly longer electron lifetime, which is attributed to the suppression of electron recombination caused by the unique TiO2 network. (C) 2016 Elsevier Ltd. All rights reserved.