Perovskite/TiO ₂ Interface Passivation Using Poly(vinylcarbazole) and Fullerene for the Photovoltaic Conversion Efficiency of 21%

Poly(vinylcarbazole) (PVCz) dispersed the typical fullerene derivative, PCBM, well in its solution, which was then coated onto a mesoporous titanium oxide (TiO ₂ ) layer. PVCz served as a scaffold to fix PCBM homogeneously and to prevent its elution out upon the following perovskite layer formation. A series of perovskite cells were fabricated upon the PVCz/PCBM-modified TiO ₂ layer. Many of the cells were characterized by a photovoltaic conversion efficiency of >20%, and the top cells had an efficiency of 21.1% (with an average of 21.0%). Fluorescence decay from the perovskite layer of the cell was unchanged with the PVCz/PCBM modification, suggesting an efficient charge transport to the electron-transporting layers. On the other hand, the PVCz/PCBM modification or passivation significantly reduced electroluminescence intensity under an inverse bias application, supporting an efficient suppression of carrier recombination at the TiO ₂ and perovskite interface.