Quasi-2D Hybrid Organic-Inorganic Perovskites: DFT Modeling Approach

Hybrid organic-inorganic perovskites (HOIPs) exhibit superior optical properties due to their relatively high photoluminescence quantum efficiency and high brightness emission. Furthermore, HOIPs have garnered much interest due to their tunable bandgaps, which are controlled by modifying the dimensionality and composition of the perovskites. In this study, we utilize DFT methods to investigate the emission of HOIPs to achieve reliable tunability of bandgap. While it has been shown that the size of the organic cations occupying the cuboctahedral cavity of 3D perovskites indirectly affect bandgap by altering B-X orbital overlap through octahedral distortions, the effect of the spacer size (in the interlayer region) has not been fully understood in quasi-2D perovskites. Using DFT, we characterize a correlation between the steric size of the spacer cation and band gap, which is a key characteristic for the design of optoelectronics. In addition to controlling the spacer composition, it has been well known that the band gap of perovskites can be tuned by controlling and mixing the halide compositions. However, despite the ability to precisely tune their bandgap energies, these mixed halide perovskites suffer from significant spectral instability, which obstructs their utilization for the design of optoelectronic devices. Here, DFT is used to reveal the source of this spectral instability due to the redistribution of the mixed anions. Our mechanistic studies provide insights into two different methods for band gap tuning of HOIPs and the fundamental reasons for the spectral instability of devices based on mixed halide compositions.