(244e) First-Principles Investigation of Band-Gap Tuning in 2D Hybrid Organic-Inorganic Perovskites

Hybrid organic-inorganic perovskites (HOIPs) have garnered considerable interest for various applications, owing to their exceptional electrical and optical properties such as high photoluminescence quantum efficiency and bright emission. This study utilizes density-functional theory (DFT) methods to examine structure-bandgap relationships in 2D HOIPs with the goal of fine-tuning their properties for diverse optoelectronic applications. In particular, the impact of spacer size in the interlayer region of 2D HOIPs remains unclear. Our DFT analysis reveals a crucial correlation between the steric size of organic spacer moieties and the perovskite bandgap. Although perovskite bandgaps can be adjusted by mixing halides, providing precise tunability of optical properties through controlled halide composition, mixed halide perovskites exhibit detrimental spectral instability, hindering their commercial use in LED applications. Using the nudged elastic band (NEB) method, our DFT calculations uncover the root cause of this spectral instability: the redistribution of the mixed halides. Our mechanistic investigation with DFT offers critical insights into achieving bandgap tuning in HOIPs and sheds light on the fundamental factors behind the observed spectral instability in devices containing mixed halide compositions.