Conformal coverage of TiO2 compact layers for high-efficient planar heterojunction perovskite solar cells

Abstract The optimization of the hole-blocking layer in perovskite solar cells (PeSCs), typically based on TiO 2 , is utmost importance, as it strongly affects the device performance. The main purpose of a compact TiO 2 (c- TiO 2 ) film is to minimize electron-hole recombination between fluorine-doped tin dioxide (FTO) and perovskite. Here, a facile way to deposit c- TiO 2 film is performed by doping the pristine titanium isopropoxide precursor with titanium tetrachloride (TiCl 4 ), a distinct enhancement in the PeSC performance is observed. The PeSC based on 10% TiCl 4 doped precursor achieves an efficiency up to 20%, presenting almost 43% enhancement compared to the pristine c-TiO 2 based counterparts. The morphological and structural analyses clarify that the doped precursor not only forms the condense TiO 2 film, but also conformally covers on the FTO substrate. Steady-state photoluminescence spectroscopy and electrical impedance spectroscopy were conducted to study interface engineering and charge carrier dynamics, which correlates the different behavior of the c- TiO 2 layers to the photovoltaic performance. Our results suggest that conformal coverage of c-TiO 2 is more beneficial for electron transfer and transport between perovskite and FTO, which significantly alleviates charge recombination and then improves the device performance.