Record Photocurrent Density over 26 mA cm−2 in Planar Perovskite Solar Cells Enabled by Antireflective Cascaded Electron Transport Layer

Planar perovskite solar cells (PSCs) hold promise for simple processing at low temperatures; however, they usually show lower short‐circuit current density ( J sc ) than their mesoporous counterparts owing to their higher primary optical reflection losses at the front side. The antireflective nature of a mesoporous electron transport layer (ETL) enables a low optical reflection in the front surface of solar cells, which is challenging to realize in planar PSCs. Herein, an antireflective cascaded ETL structure using SnO 2 /TiO 2 –Cl bilayers is devised to reduce optical reflection losses and to improve electrical performance in planar PSCs. The antireflective cascaded ETL results in an enhanced J sc of 25.4 mA cm −2 in formamidinium lead triiodide based planar PSCs, compared with the control J sc of 24.6 mA cm −2 using single‐layered SnO 2 ETL. A record‐high J sc of 26.1 mA cm −2 is further achieved using an additional antireflective coating on the front glass side, leading to a power conversion efficiency of 22.9%.