Highly Localized Resonant Excitons in Silver-Pnictogen Halide Double-Perovskites
Raisa-Ioana Biega a b, Marina R. Filip c d e, Linn Leppert b a, Jeffrey B. Neaton d e f g
a Institute of Physics, University of Bayreuth, Germany, Bayreuth, Germany
b University of Twente, MESA+ Institute for Nanotechnology, Netherlands
c University of Oxford, Department of Physics, Clarendon Laboratory, UK, Parks Road, United Kingdom
d University of California Berkeley, Department of Physics, United States
e Molecular Foundry, Lawrence Berkeley National Laboratory, California 94720, USA, United States
f Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA, Berkeley, United States
g Kavli Energy NanoSciences Institute at Berkeley, United States
Online Conference
Proceedings of Internet Conference on Theory and Computation of Halide Perovskites (ComPer)
Online, Spain, 2020 September 8th - 9th
Organizers: Giacomo Giorgi and Linn Leppert
Oral, Raisa-Ioana Biega, presentation 017
Publication date: 4th September 2020

Power conversion efficiencies of single junction solar cells with lead-based halide perovskite absorbers have recently exceeded 25%. However, stability and toxicity concerns have stimulated great efforts for finding lead-free compounds with similar advantageous optoelectronic properties, i.e., small band gaps, low effective masses, and small exciton binding energies. Double perovskites containing alternating mono- and trivalent metal cations such as silver and bismuth, instead of lead, have emerged as one such alternative [1], [2]. However, the nature of optical excitations in these systems is not yet well understood[3], [4], [5], [6], [7].

Here we present first principles calculations of the electronic structure and excited states of the double perovskites Cs2AgBX6 (B=Bi3+, Sb3+ and X=Br-, Cl-). We use density functional theory and ab initio many-body perturbation theory within the GW approximation and the Bethe-Salpeter equation approach to calculate band structures and optical excitations of these materials. We find that this family of materials exhibit exceptionally high exciton binding energies, of a magnitude typically observed in 2D and 1D semiconductors. Our results provide insights into the nature of optical excitations of this group of materials and their suitability for photovoltaic and other light harvesting applications.

This work was supported by the Bavarian State Ministry of Science and the Arts through the Collaborative Research Network Solar Technologies go Hybrid (SolTech), the Elite Network Bavaria, and the German Research Foundation (DFG) through SFB840 B7, and through computational resources provided by the Bavarian Polymer Institute (BPI). R.B. acknowledges support by the DFG program GRK1640. MRF and JBN were supported by the Center for Computational Study of Excited-State Phenomena in Energy Materials (C2SEPEM) at the Lawrence Berkeley National Laboratory, which is funded by the U. S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-C02-05CH11231. The authors would like to acknowledge computational resources at the Molecular Foundry, also supported by the Office of Science, Office of Basic Energy Sciences, of the US DOE under Contract DE-AC02-5CH11231 and resources of the National Energy Research Scientific Computing Center (NERSC).

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