The logic in the design of a halide-mixed APb(I_1−xBr_x)₃ perovskite is quite straightforward: to combine the superior photovoltaic qualities of iodine-based perovskites with the increased stability of bromine-based perovskites. However, even small amounts of Br doped into the iodine-based materials leads to some instability. In the present report, using first-principles computations, we analyzed a wide variety of α-CsPbI₂Br and β-CsPbI₂Br phases, compared their mixing enthalpies, explored their oxidative properties, and calculated their hole-coupled and hole-free charged Frenkel defect (CFD) formations by considering all possible channels of oxidation. Nanoinclusions of bromine-rich phases in α-CsPbI₂Br were shown to destabilize the material by inducing lattice strain, making it more susceptible to oxidation. The uniformly mixed phase of α-CsPbI₂Br was shown to be highly susceptible towards a phase transformation into β-CsPbI₂Br when halide interstitial or halide vacancy defects were introduced into the lattice. The rotation of PbI₄Br₂ octahedra in α-CsPbI₂Br allows it either to transform into a highly unstable apical β-CsPbI₂Br, which may phase-segregate and is susceptible to CFD, or to phase-transform into equatorial β-CsPbI₂Br, which is resilient against the deleterious effects of hole oxidation (energies of oxidation >0 eV) and demixing (energy of mixing <0 eV). Thus, the selective preparation of equatorial β-CsPbI₂Br offers an opportunity to obtain a mixed perovskite material with enhanced photostability and an intermediate bandgap between its constituent perovskites.

A theoretical defect formation energy study on FAPbCl ₃ reveals importance of optoelectronic structure.

A tiered forcefield/semiempirical/ meta -GGA pipeline together with a thermodynamic scheme designed with error cancellation in mind was developed to calculate binding energies of [2.2.2] cryptate complexes of mono- and divalent cations.

We investigate the defect-dependent electronic structure and gas-sensing potential of cubic α-CsPbI₃ using first-principles density functional theory and nonadiabatic molecular dynamics. Among the intrinsic defects, interstitials, vacancies, antisites, and switches studied, the I_Pb and Pb_I antisite defects exhibit transition energy levels near the middle of the band gap, thus functioning as deep traps. Short-term adsorption of ammonia selectively modifies the electronic structure, coordinating with Pb at Pb_I sites and Cs at I_Pb sites, significantly altering recombination pathways. Detailed analysis reveals that NH₃ reduces anharmonicity at I_Pb defects, enabling enhanced recombination at elevated temperatures, while trap-assisted recombination dominates at room temperature. Other analytes, including CH₃NH₂ and NO₂, show negligible impact on the band gap or recombination dynamics, highlighting the potential selectivity of NH₃ interactions. Ab initio nonadiabatic molecular dynamics simulations at 300 K and 600 K further demonstrate temperature-dependent modulation of carrier lifetimes, with NH₃ accelerating recombination at ambient conditions and suppressing certain pathways at higher temperatures. These findings suggest that α-CsPbI₃ can serve as a selective and sensitive ammonia sensor over a broad temperature range and offer insights for ammonia detection under industrially relevant conditions.

We investigate the defect-dependent electronic structure and gas-sensing potential of cubic α-CsPbI₃ using first-principles density functional theory and nonadiabatic molecular dy-namics simulations. Among the intrinsic defects, interstitials, vacancies, antisites, and switches studied, the IPb and PbI antisite defects exhibit transition energy levels near the middle of the band gap, thus functioning as deep traps. Short-term adsorption of ammo-nia selectively modifies the electronic structure, coordinating with Pb at PbI sites and Cs at IPb sites, significantly altering recombination pathways. Detailed analysis reveals that NH3 reduces anharmonicity at IPb defects, enabling enhanced recombination at elevated tem-peratures, while trap-assisted recombination dominates at room temperature. Other ana-lytes, including CH3NH2 and NO2, show negligible impact on the band gap or recombina-tion dynamics, highlighting the selectivity of NH3 interactions. Ab initio nonadiabatic mo-lecular dynamics simulations at 300 K and 600 K further demonstrate tempera-ture-dependent modulation of carrier lifetimes, with NH3 accelerating recombination at ambient conditions and suppressing certain pathways at higher temperatures. These findings suggest that α-CsPbI₃ can serve as a selective and sensitive ammonia sensor over a broad temperature range and offer insights for ammonia detection under industrially relevant conditions.