Amorphous Tin Oxide as a Low-Temperature-Processed Electron-Transport Layer for Organic and Hybrid Perovskite Solar Cells

Chemical bath deposition (CBD) of tin oxide (SnO2) thin films as an electron-transport layer (ETL) in a planar-heterojunction n–i–p organohalide lead perovskite and organic bulk-heterojunction (BHJ) solar cells is reported. The amorphous SnO2 (a-SnO2) films are grown from a nontoxic aqueous bath of tin chloride at a very low temperature (55 °C) and do not require postannealing treatment to work very effectively as an ETL in a planar-heterojunction n–i–p organohalide lead perovskite or organic BHJ solar cells, in lieu of the commonly used ETL materials titanium oxide (TiO2) and zinc oxide (ZnO), respectively. Ultraviolet photoelectron spectroscopy measurements on the glass/indium–tin oxide (ITO)/SnO2/methylammonium lead iodide (MAPbI3)/2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene device stack indicate that extraction of photogenerated electrons is facilitated by a perfect alignment of the conduction bands at the SnO2/MAPbI3 interface, while the deep valence band of SnO2 ensures stro...