Can Chelatogenic Molecules Enhance Air-Processed MAPbI3 Perovskite Solar Cells Stability? Salophen's Case Study

Abstract

Perovskite solar cells attracted attention in last years due to their low-cost fabrication and high-power conversion efficiency. For practical applications, however, long-term stability is still a problem. The perovskite layer degrades when exposed to moisture, oxygen, temperature and UV radiation. One strategy to overcome this limitation includes modification/passivation of the perovskite layer. The use of chelatogenic molecules is an effective way because their functional groups can coordinate with the metallic center (Pb2+) of the perovskite, enhancing its structural stability. Herein, we demonstrate the effect of incorporating N,N’-bis(salicylidene)-o-phenylenediamin (salophen) molecules (a Schiff base) on the methylammonium lead iodide perovskite (MAPbI3) thin film. Salophen was dissolved in ethyl acetate solvent in five different concentrations and spin-coated onto MAPbI3, during the antisolvent step in ambient conditions (room temperature; relative humidity over 50%). X-ray diffractograms reveal that the addition of salophen molecules on the top of the MAPbI3 films induces a better crystallization of the perovskite α-phase, eliminating the residual amount of PbI2, at same time that creates a hydrophobic protective surface. Stead-state photophysical characterization shows that salophen molecules did not significantly change the optical properties of the MAPbI3 films. Nonetheless, time-resolved photoluminescence decays clearly exhibit a charge-carrier extraction pathway through salophen passivation of MAPbI3 defects, while enhances the thin film organization, a behaviour proved with surface electron microscopy images. Device efficiencies reached values higher than 18% alongside gains in stability.