Lead-Free Alloyed Double Perovskites: An Emerging Class of Materials for Optoelectronic Applications

Abstract

Lead-free all-inorganic alloyed double perovskites have redefined the photovoltaic research in the recent past. However, a detailed study of their optical, excitonic, polaronic, and transport properties remains unexplored. Here, we investigate the variation of carrier-lattice interaction and optoelectronic properties of pristine as well as alloyed Cs2AgInCl6 double perovskites using a combined state-of-the-art many-body perturbation theory and density functional perturbation theory. Our results reveal that, in comparison to a pristine material, alloyed compounds have a longer exciton lifetime, indicating a lower electron–hole recombination in the latter. This also leads to a higher quantum yield and conversion efficiency in the alloyed compounds. The phonon scattering is found to limit the charge carrier mobilities and, thus, plays an important role in the development of high-efficiency perovskite photovoltaics. Dominant carrier-phonon scattering is also observed via the Fröhlich mechanism near room temperature. A significant increase in hole and electron mobilities is noticed in alloyed perovskites in comparison to its pristine counterpart making the former more potent in photovoltaic devices.

Tunable near-infrared emission and three-photon absorption in lanthanide-doped double perovskite nanocrystals

“…Theoretically, the value of μ for Cs 2 AgInCl 6 was estimated to be 0.23 m 0 . 97 Our obtained value of μ for undoped Cs 2 AgInCl 6 is consistent with previously reported theoretical work. In this way, by analysing the closed-aperture Z -scan with the help of a two-band model we are able to estimate the value of μ , which is the fundamental physical parameter in perovskite materials.…”

“…E B is the difference between the energy of an exciton (electrons and holes are bounded by a screened Coulomb interaction) and the energy of an unbound non-interacting electron–hole pair. If we took ε eff = 3.77 from the previous theoretical report, 97 we estimated E B = 0.23 eV. Therefore, from these analyses, it is possible to estimate the exciton binding energy also.…”

Emerging Opportunities in Lead-Free and Lead–Tin Perovskites for Environmentally Viable Photodetector Applications

“…We can envisage the double perovskite as isolated metal halide octahedral anions surrounded by inorganic cations. A high exciton binding energy, more significant bandgaps, smaller band dispersions, and a higher charge carrier effective mass are the consequences of isolating metal halide octahedral anions. , The Cs 2 SnI 6– x Br x ( x = 0–3) structure has been widely investigated in Sn-based vacancy-ordered halide double perovskites …”

“…A high exciton binding energy, more significant bandgaps, smaller band dispersions, and a higher charge carrier effective mass are the consequences of isolating metal halide octahedral anions. 63,64 The Cs 2 SnI 6−x Br x (x = 0−3) structure has been widely investigated in Sn-based vacancy-ordered halide double perovskites. 65 Other types of crystal structures were also observed.…”

Chemical Mapping of Excitons in Halide Double Perovskites

“…First-principles many-body perturbation theory within the GW approximation and the Bethe–Salpeter equation , (BSE) approach has played a particularly important role in quantitatively predicting the electronic and excited-state structure of halide perovskites. In particular, comparison of GW +BSE calculations with the Wannier–Mott model has demonstrated the hydrogenic nature of excitons in Pb-based halide perovskites , and in the double perovskite Cs 2 AgInCl 6 . , In contrast, we and others recently showed that the double perovskite family Cs 2 AgBX 6 (B = Bi or Sb, and X = Br or Cl) ,, exhibits resonant excitons with binding energies between 170 and 450 meV, which are strongly localized, with fine structural features that differ from those computed using the hydrogenic model. , We assigned the nonhydrogenic character of excitons in these halide double perovskites to their chemical heterogeneity giving rise to an anisotropic electronic structure and dielectric screening . For other halide double perovskites, optoelectronic properties and exciton binding energies were also shown to vary significantly. − The picture that emerges from these reports suggests a rich landscape of excitons in halide double perovskites and calls for systematic mapping of this landscape using first-principles calculations.…”