Role of carbon nanodots in defect passivation and photo-sensitization of mesoscopic-TiO2 for perovskite solar cells

In this work, a recently developed carbon nanodots (CnDs) were introduced in the mesoscopic TiO2 to form a TiO2: CnDs composite, to be used as an electrode in CH3NH3PbI3 based perovskite devices. It resulted the improvement in morphology of perovskite film and induced a carbon-doping passivating the oxygen defects. In addition, the presence of carbon dots enhanced the charge carrier mobility of TiO2 and provided extra photo-generation ability to the perovskite device due to its absorbing nature. The improved morphology, carbon-doping, photogeneration ability and the improved charge transfer characteristics with the introduction of carbon dots was verified by the scanning electron microscopy (SEM), atomic force microscopy (AFM), X-Ray photoelectron spectroscopy (XPS), UV-visible absorption, X-ray diffraction, space charge limited current (SCLC) measurement, photoluminescence (PL), electrochemical impedance spectroscopy (EIS), current leakage and open circuit photovoltage decay (OCPD) measurements. An optimized concentration of CnDs (3 wt%) within the TiO2 resulted in a maximum power conversion efficiency of 19.45% with negligible hysteresis, which is 16% higher than the device with pristine TiO2. (c) 2019 Published by Elsevier Ltd.