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 SnO2/TiO2-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 SnO2 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%.