Manganese Porphyrin Interface Engineering in Perovskite Solar Cells

An interfacial engineering approach was adopted in order to optimize the photovoltaic parameters and the stability of n-i-p planar perovskite solar cells (PSCs). A thin manganese (Mn) porphyrin [(TMePyP)I4Mn(AcO)] layer was introduced between the titania (TiO2) electron transport layer (ETL) and the perovskite absorber. The introduction of porphyrin onto the TiO2 substrate provoked a significant decrease in the work function (WF), which arose from the large local dipole moment. The modification also provided a more hydrophobic environment that favored the growth of homogeneous and large perovskite crystals. Moreover, the electron charge transport to the ETL was facilitated via the highly paramagnetic character of the Mn porphyrin, whereas the negative impact of humidity and oxygen on the PSC performance was hindered. Density functional theory analysis justified the observed large decrease of the WF and the strong electronic coupling of porphyrin with the TiO2 compact layer (following the porphyrin deposition), which are beneficial for electron extraction. By combining the Mn porphyrin and the CH3NH3PbI3 perovskite, significant enhancement of the stabilized power conversion efficiency by 22% was recorded. The shelf-shield stability was also improved after more than 600 h of storage in the dark under ambient conditions.