First-principles prediction of electronic band structures of materials is crucial for rational material design, especially in solar-energy-related materials science. Hybrid functionals that mix the Hartree-Fock exact exchange with local or semilocal density functional approximations have proven to be accurate and efficient alternatives to more sophisticated Green's function-based many-body perturbation theory. The optimal fraction of the exact exchange, previously often treated as an empirical parameter, is closely related to the screening strength of the system under study. From a physical point of view, the screening has two extreme forms: the dielectric screening [1/ϵ] that is dominant in wide-gap materials and the Thomas-Fermi metallic screening [exp(-ζ r) ] that is important in narrow-gap semiconductors. In this work, we have systematically investigated the performances of a nonempirical doubly screened hybrid (DSH) functional that considers both screening mechanisms and found that it excels all other existing hybrid functionals and describes the band gaps of narrow-, medium-, and wide-gap insulating systems with comparably good performances.

Double halide perovskites are a class of promising semiconductors applied in photocatalysis, photovoltaic devices, and emitters to replace lead halide perovskites, owing to their nontoxicity and chemical stability. However, most double perovskites always exhibit low photoluminescence quantum efficiency (PLQE) due to the indirect bandgap structure or parity‐forbidden transition problem, limiting their further applications. Herein, the self‐trapped excitons emission of Cs2NaInCl6 by Sb‐doping, showing a blue emission with high PLQE of 84%, is improved. Further, Sb/Mn codoped Cs2NaInCl6 nanocrystals are successfully synthesized by the hot‐injection method, showing a tunable dual‐emission covering the white‐light spectrum. The studies of PL properties and dynamics reveal that an energy transfer process can occur between the self‐trapped excitons and dopants (Mn2+). The work provides a new perspective to design novel lead‐free double perovskites for realizing a unique white‐light emission.

Indium (In)-based halide perovskites are desirable for next-generation phosphors and emitting devices, due to their broad emission, nontoxicity, and oxidization avoidance capabilities. However, the In-based perovskites always exhibit low external photoluminescence quantum efficiency (PLQE) as a result of their weak light absorption near the corresponding excitation region, and thus, are limited in extended applications. Herein, we have developed an antimony (Sb)-doping strategy to improve the absorption ability of Cs 2 InCl 5 •H 2 O in the ultraviolet region. Excitingly, we obtained a warm-light phosphor with ultrahigh external (internal) PLQE of 72.8% (86.7%). Typically, upon 1.5% Sb doping, the single-crystalline Cs 2 InCl 5 •H 2 O perovskite displayed a stronger warm-light emission at ∼ 610 nm with a large Stokes shift of 295 nm and full width at half maximum (FWHM) of 164 nm. Density functional theory (DFT) calculations revealed that the Sb-doping induced an impurity level in the bandgap, increasing the density of state (DOS), and promoted more carriers into the conduction band maximum. Furthermore, external PLQE from 18% to 59% could be realized in other zero-dimensional In-based perovskites through the same doping strategy.