Propriedades optoeletrônicas e estruturais de perovskitas híbridas de baixa dimensionalidade

Abstract

Thin films of semiconductors based on three-dimensional hybrid halide perovskites (3D-HHPs) have been attracting attention and are being applied in the efficient conversion of sunlight into electrical energy. Despite the record efficiencies achieved by solar cells based on methylammonium lead iodide (MAPbI3) 3D-HHPs, the inherent chemical instability of the ionic structure remains a challenge to overcome. In this context, the present work aims to investigate and correlate the structural factors governing the chemical stability of two-dimensional perovskites (2D-HHPs) under temperature variations and light exposure in thin films containing 2D-HHPs. To this end, semiconductors were synthesized in the form of 2D-HHP single crystals: tyramine (Tyr2PbI4) and methoxybenzylamine (Mtx2PbI4) tetraiodoplumbate(II). X-ray diffraction results of Mtx2PbI4 and Tyr2PbI4 single crystals confirmed crystallization in orthorhombic (Pbca) and triclinic [(P1 ̅(2)] symmetries, respectively, with average hydrogen bond (H···I) distances between the organic cations and the octahedral (inorganic) network of 2.8488 Å and 2.9117 Å, respectively. The study of electronic properties through diffuse reflectance revealed excitonic bands in the Mtx2PbI4 (Tyr2PbI4) single crystal centered at 2.27 eV and 2.41 eV (2.25 eV and 2.41 eV), with an optical bandgap of 3.11 eV (3.15 eV). Photoluminescence results at cryogenic temperatures for the Tyr2PbI4 crystal showed strong exciton-phonon coupling with an energy of 219.86 meV. A comparison of X-ray diffraction for Tyr2PbI4 at 298 K and 100 K confirmed the prevalence of the triclinic symmetry. The surface treatment of MAPbI3 (3D) thin films with a tyramine (2D - Tyr2PbI4) solution significantly improved stability under degradation conditions for 24 hours (air, humidity, and TiO2), because of hydrogen bonds that passivate and protect the outer layers of MAPbI3 thin films.