Proceedings of Internet Conference on Theory and Computation of Halide Perovskites (ComPer)
Publication date: 4th September 2020
First principles understanding of the interaction of photo-excited electrons and holes in semiconductors and insulators is of crucial importance for developing novel light absorbers and light emitters for optoelectronic applications. Bound electron-hole pairs (excitons) are screened by the dielectric environment, which generally originates both from electrons and phonons. The GW approximation and the Bethe-Salpeter Equation (GW+BSE) constitute the state of the art methodological framework for understanding the Physics of optical excitations. However, standard GW+BSE formalism neglects dynamical lattice effects on the dielectric screening, and accounts only for the electronic contribution. In this talk I will present our recent ab initio generalization of the BSE to include the contribution of dynamic phonon screening effects to the electron-hole interaction [1]. We will show that phonon screening effects reduce the exciton binding energy by more than a factor of 2, and lead to an improved agreement with experiment for a wide range of semiconductors including lead-halide perovskites CsPbX3 (X=Cl, Br, I), as well as semiconductors within the III-V, and II-VI series. This result is in very good agreement with prior experimental [2] and theoretical works [3]. We rationalize our results, using a generalized Wannier-Mott model which includes phonon screening from a single dispersionless polar mode, and discuss the general intuition for phonon contribution to the exciton binding energy.
[1] Filip, Haber & Neaton, In Review (2020)
[2] Miyata et al, Nat. Phys. 11, 582 (2015)
[3] Umari et al, JPCL, 9 , 3 ,620 (2018)
This work was supported by the US Department of Energy within the C2SEPEM center, and benefited from computational resources at the National Energy Research Scientific Computing Center (NERSC) and the Texas Advanced Computing Center (TACC).
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