An annealing-free aqueous-processed anatase TiO2 compact layer for efficient planar heterojunction perovskite solar cellsElectronic supplementary information (ESI) available: Experimental details including synthesis, experimental procedure and supporting data. See DOI: 10.1039/c7cc01104k

A facile aqueous-based fabrication scheme is developed for producing annealing-free anatase TiO 2 (AF-TiO 2 ) films that exhibit efficient electron transport properties in planar heterojunction perovskite solar cells (PSCs). AF-TiO 2 films are fabricated by spin coating on a substrate a colloidal solution of anatase TiO 2 nanoparticles (NPs) prepared via a low temperature hydrolytic sol-gel method. The resultant AF-TiO 2 films show low electrical resistance, high transmittance in the visible and near-infrared regions and facilitation of high-quality perovskite film formation, which can be attributed to their homogeneous surface morphology and nanocrystallinity. The AF-TiO 2 based PSCs achieve a power conversion efficiency (PCE) of 18.29 ± 0.18%, showing significant improvement compared to the control PSCs (PCE = 11.33 ± 0.32%) based on TiO 2 films made by high-temperature annealing of amorphous TiO 2 (HTA-TiO 2 ). We report efficient perovskite solar cells (PCE = 18.29 ± 0.18%) based on TiO 2 films synthesised via a facile aqueous, annealing-free route.