Honeycomb-Type TiO₂ Films Toward a High Tolerance to Optical Paths for Perovskite Solar Cells

Given the advantages of high power conversion efficiencies (PCEs), antisolvent-step free production, and suitability for device production in ambient conditions, perovskite solar cells (PSCs) based on ionic-liquid solvents have attained particular research interest. To further improve device performance, light management could be optimized to increase light harvesting in the perovskite layer. Here, ordered honeycomb-like TiO₂ (Hc-TiO₂) structures with a periodicity of around 450 nm were fabricated through a sacrificial template method. With this photonic crystal structure, the control to light flow and the confinement effect for perovskite growth were achieved simultaneously in the Hc-TiO₂, leading to improved light absorption as well as preferred crystal orientation. Furthermore, a reduced trap-state density and a well-aligned energy level induced by the perovskite/pore interlayer facilitated the charge-carrier extraction from the perovskite layer to electron transport layer. As a result, the structured devices performed better than the planar cells. And the angular dependent J–V sweeps show that the structured device reserved 76 % of its initial short circuit current density (J_sc), whereas the planar cell showed more than a half loss under the incident light of 40°, demonstrating a reduced downward trend in J_sc with the presence of photonic crystal structures. This occurrence also suggests that the structured PSCs in this work have a high tolerance to optical path changes.