Nanoparticulate Metal Oxide Top Electrode Interface Modification Improves the Thermal Stability of Inverted Perovskite Photovoltaics

Solution processed {\gamma}-Fe2O3 nanoparticles via the solvothermal colloidal synthesis in conjunction with ligand-exchange method are used for interface modification of the top electrode in inverted perovskite solar cells. In comparison to more conventional top electrodes such as PC(70)BM/Al and PC(70)BM/AZO/Al, we show that incorporation of a {\gamma}-Fe2O3 provides an alternative solution processed top electrode (PC(70)BM/{\gamma}-Fe2O3/Al) that not only results in comparable power conversion efficiencies but also improved thermal stability of inverted perovskite photovoltaics. The origin of improved stability of inverted perovskite solar cells incorporating PC(70)BM/ {\gamma}-Fe2O3/Al under accelerated heat lifetime conditions is attributed to the acidic surface nature of {\gamma}-Fe2O3 and reduced charge trapped density within PC(70)BM/ {\gamma}-Fe2O3/Al top electrode interfaces.