Decisive role of electron–hole and carrier–phonon interactions on luminescence performance of double perovskite Rb2HfCl6

All-inorganic lead-free vacancy-ordered halide double perovskite (VOHDP) have been attracting significant attention as a promising candidate for white light-emitting diodes, but the fundamental insight remains unclear. Here, we report a first-principles study of quasiparticle band structure, excitonic, and carrier transport properties of Rb2HfCl6 using the G0W0 plus Bethe–Salpeter equation and Boltzmann transport equation calculations. We reveal that the band-to-band transition in Rb2HfCl6 with a direct bandgap of 7.07 eV is parity-forbidden and the transition occurs via exciton with an excitation energy of 6.36 eV and a strong binding energy of 0.67 eV. Our calculations demonstrate that carrier scattering is dominantly affected by the polar optical phonons, and carrier mobilities are much smaller than those of the hybrid halide perovskites. This work highlights strong electron–hole and carrier–phonon interactions in the VOHDPs, leading to a localization of carriers favorable for the light emission applications.