Improving the Optoelectronic Properties of Mesoporous TiO2 by Cobalt Doping for High-Performance Hysteresis-free Perovskite Solar Cells.

We for the first time report the incorporation of cobalt into a mesoporous TiO2 electrode for application in perovskite solar cells (PSCs). The Co-doped PSC exhibits excellent optoelectronic properties; we explain the improvements by passivation of electronic trap or sub-band-gap states arising due to the oxygen vacancies in pristine TiO2, enabling faster electron transport and collection. A simple postannealing treatment is used to prepare the cobalt-doped mesoporous electrode; UV-visible spectroscopy, X-ray photoemission spectroscopy, space charge-limited current, photoluminescence, and electrochemical impedance measurements confirm the incorporation of cobalt, enhanced conductivity, and the passivation effect induced in the TiO2. An optimized doping concentration of 0.3 mol % results in the maximum power conversion efficiency of 18.16%, 21.7% higher than that of a similar cell with an undoped TiO2 electrode. Also, the device shows negligible hysteresis and higher stability, retaining 80.54% of the initial efficiency after 200 h.