Perovskite solar cells (PSCs) exceeding a power conversion efficiency (PCE) of 20% have mainly been demonstrated by using mesoporous titanium dioxide (mp-TiO 2 ) as an electron-transporting layer. However, TiO 2 can reduce the stability of PSCs under illumination (including ultraviolet light). Lanthanum (La)-doped BaSnO 3 (LBSO) perovskite would be an ideal replacement given its electron mobility and electronic structure, but LBSO cannot be synthesized as well-dispersible fine particles or crystallized below 500°C. We report a superoxide colloidal solution route for preparing a LBSO electrode under very mild conditions (below 300°C). The PSCs fabricated with LBSO and methylammonium lead iodide (MAPbI 3 ) show a steady-state power conversion efficiency of 21.2%, versus 19.7% for a mp-TiO 2 device. The LBSO-based PSCs could retain 93% of their initial performance after 1000 hours of full-Sun illumination.
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