Boosting the Stability at Room Atmosphere of Lead Halide Perovskites Through a Simultaneous Compositional Tuning of the A-and X-sites

Abstract

Organic-inorganic lead halide perovskites, particularly the Formamidinium and Cesium based-ones are among the most promising materials for photovoltaic applications, yet they still face a stability issue. In this work, we boosted their structural and environment-resistance stability by the simultaneous compositional tuning of their A-cation and X-anion sites. We prepared 9 different solutions of Cs_xFA_1-xPb(I_1-yBr_y)₃ (x = 0.1, 0.2 and 0.3 and y = 0.15, 0.25 and 0.35), made the deposition on FTO substrates by one step spin-coating technique and did the post-annealing at 120 °C instead of the 350 °C for CsPbI₃ for instance. We, afterward, characterized the films by X-ray diffraction (XRD), UV-visible spectroscopy, photoluminescence (PL) levels and Field Emission Scanning Electron Microscopy (FESEM) to assess their crystallinity, optical properties and morphology. As a result, we noted that they all crystallized into the perovskite black α-phase and remained stable after 3 weeks in contrast to FAPbI₃ or CsPbI₃. We also found that their band gap energy ranged between 1.62 eV (for the compounds with 15% of Br) to 1.75 eV, hence their excellent absorbance properties.