The Role of Thickness Control and Interface Modification in Assembling Efficient Planar Perovskite Solar Cells

Perovskite solar cells (PSCs) have achieved tremendous success within just a decade. This success is critically dependent upon compositional engineering, morphology control of perovskite layer, or contingent upon high-temperature annealed mesoporous TiO₂, but quantitative analysis of the role of facile TiCl₄ treatment and thickness control of the compact TiO₂ layer has not been satisfactorily undertaken. Herein, we report the facile thickness control and post-treatment of the electron transport TiO₂ layer to produce highly efficient planar PSCs. TiCl₄ treatment of TiO₂ layer could remove the surface trap and decrease the charge recombination in the prepared solar cells. Introduction of ethanol into the TiCl₄ aqueous solution led to further improved open-circuit voltage and short-circuit current density of the related devices, thus giving rise to enhanced power conversion efficiency (PCE). After the optimal TiCl₄ treatment, PCE of 16.42% was achieved for PSCs with TiCl₄ aqueous solution-treated TiO₂ and 19.24% for PSCs with TiCl₄ aqueous/ethanol solution-treated TiO₂, respectively. This work sheds light on the promising potential of simple planar PSCs without complicated compositional engineering and avoiding the deposition and optimization of the mesoporous scaffold layer.