Investigation of the stability of organic-inorganic halide perovskite thin films: Insight from experimental and simulation.

Herein, we investigated the stability of lead halide perovskites under ambient conditions after mixing the two cations Formamidinium (FA) and Cesium (Cs). The CsFAPbI perovskites solutions were prepared with different contents of x (0.0, 0.3, 0.5, 0.7 and 1.0) and deposited on substrates by spin-coating technique. The CsFAPbI films were, afterwards, characterized using the X-ray diffraction (XRD), UV-visible spectroscopy, photoluminescence (PL) spectra and scanning electron microscopy (SEM) to figure out their crystallinity, morphology, and optical properties. We noticed a stable perovskite structure for the mixed compounds unalike the pure FA and Cs films. The XRD analysis revealed, even after two weeks, the growth and good stability after two weeks of the desired black cubic α-phase perovskite structure in opposite to FAPbI and CsPbI which, respectively, showed faster degradation and transition into non-perovskite δ-phase and ɣ-phase no perovskite phases. The mixed perovskites Cs-FA also displayed a high absorbance especially for the ones with 30% of Cs and 70% of FA or 50% of each, with an excellent band gap energy ranging between 1.52 and 1.7 eV where FAPbI and CsPbI were showing a bandgap between 1.5 and 1.9 eV respectively. Moreover, the performance of the CsFAPbI based solar cells were simulated with SCAPS by using the band gaps obtained from the experimental study and after by varying the band gap, the thickness of the absorber layers and then different types of Electron Transport Layer (ETL). The simulation results revealed that the CsFAPbI based solar cells had the highest higher efficiency around 22.36%.