Doubling the Stakes: The Promise of Halide Double Perovskites

Structural, elastic, electronic, and optical properties of lead-free halide double perovskites Cs2BꞌBꞌꞌBr6 (BꞌBꞌꞌ: BeMg, CdBe, CdGe, GeMg, GeZn, MgZn): Ab initio calculations

CONTEXT

In our study, we theoretically investigated the structural, elastic, electronic, and optical characteristics of halide double perovskites (DPs) Cs2B'B''Br6 (B'B'': BeMg, CdBe, CdGe, GeMg, GeZn, MgZn). Structural stabilities were assessed based on the enthalpy of formation, tolerance factor, and elastic constants. Ductile and brittle behavior was examined using Poisson and Pugh's ratios. Based on electronic calculations, it has been concluded that Cs2B'B''Br6 double perovskites with B'B'' as BeMg or CdBe exhibit direct bandgaps, whereas those with B'B'' as CdGe, GeMg, GeZn, or MgZn display indirect bandgaps. Additionally, we thoroughly investigated the optical properties of double perovskites by analyzing all their parameters in the energy range spanning 0 to 13 eV. Primary absorption was noted in the ultraviolet (UV) region.

METHODS

In this work, all calculations were performed using the Wien2k package. The generalized gradient approximation (GGA) and the modified Becke-Johnson (mBJ) method were employed to describe the exchange-correlation interactions.

Highly Luminescent One-Dimensional Organic-Inorganic Hybrid Double-Perovskite-Inspired Materials for Single-Component Warm White-Light-Emitting Diodes

Double perovskites (DPs) are one of the most promising candidates for developing white light-emitting diodes (WLEDs) owing to their intrinsic broadband emission from self-trapped excitons (STEs). Translation of three-dimensional (3D) DPs to one-dimensional (1D) analogues, which could break the octahedral tolerance factor limit, is so far remaining unexplored. Herein, by employing a fluorinated organic cation, we report a series of highly luminescent 1D DP-inspired materials, (DFPD)₂ M^I InBr₆ (DFPD=4,4-difluoropiperidinium, M^I =K⁺ and Rb⁺ ). Highly efficient warm-white photoluminescence quantum yield of 92 % is achieved by doping 0.3 % Sb³⁺ in (DFPD)₂ KInBr₆ . Furthermore, single-component warm-WLEDs fabricated with (DFPD)₂ KInBr₆ :Sb yield a luminance of 300 cd/m² , which is one of the best-performing lead-free metal-halides WLEDs reported so far. Our study expands the scope of In-based metal-halides from 3D to 1D, which exhibit superior optical performances and broad application prospects.