Morphology fixing agent for [6,6]-phenyl C₆₁-butyric acid methyl ester (PC₆₀BM) in planar-type perovskite solar cells for enhanced stability

Here, we report that the delamination of [6,6]-phenyl C₆₁-butyric acid methyl ester (PC₆₀BM) from the CH₃NH₃PbI₃ (MAPbI₃) layer is a critical reason for the degradation of inverted perovskite solar cells (PSCs). In this work, an ∼10 nm-thick titanium oxide (TiO_x) layer can function as a morphology-fixing agent for preventing PC₆₀BM delamination, which in turn induces greatly improved long-term stability of the PSCs. In addition, the devices with the TiO_x layer exhibited increased open circuit voltages, current densities, and fill factors, which correspond to improved initial device efficiency. Surface morphology changes of the PC₆₀BM layer on the MAPbI₃ layer during long-term operation of PSCs were confirmed by SEM and AFM, and were also found to be correlated with various electrical properties of the devices such as the hole mobility and charge generation and extraction efficiencies from the space-charge-limited current (SCLC) measurements and J_phversus V_int characterizations.