Can chelatogenic molecules enhance the stability of air-processed MAPbI3 perovskite solar cells? A case study of salophen

Abstract

Perovskite solar cells have attracted attention in recent 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 is the modification/passivation of the perovskite layer. The use of chelatogenic molecules is an effective method because their functional groups can coordinate with the metallic center (Pb²⁺) of the perovskite, thereby enhancing its structural stability. Herein, we demonstrate the effect of incorporating N,N′-bis(salicylidene)-o-phenylenediamin (salophen) molecules (a Schiff base) on methylammonium lead iodide perovskite (MAPbI₃) thin films. Salophen was dissolved in ethyl acetate solvent at five different concentrations and spin-coated onto MAPbI₃ during the antisolvent step under 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 better crystallization of the perovskite α-phase, eliminating the residual amount of PbI₂, which simultaneously creates a hydrophobic protective surface. Steady-state photophysical characterization shows that the 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 the salophen passivation of MAPbI₃ defects while enhancing thin film organization, a behaviour proven with surface electron microscopy images. Device efficiencies reached values higher than 18%, along with gains in stability.