Dynamically Screened Excitons in Heteropolar Semiconductors: The Case of Halide Perovskites

The interaction between photogenerated electron-hole pairs in semiconductors is screened by their dielectric environment. In heteropolar semiconductors, dielectric screening originates with both electrons and polar phonons. State of the art GW/BSE methods for prediction of excitons typically only include the static electronic contribution to the screening. However, prior studies report on the importance of dynamical lattice contributions to screening from polar phonons for excitons in halide perovskites [1,2]. Here, we develop an extension of the BSE approach to include both electronic and lattice contributions to the dielectric screening. We show that in heteropolar semiconductors, lattice effects can significantly reduce the electron-hole interaction, even when the exciton binding energy is much larger than the characteristic phonon frequency. We demonstrate the importance of dynamical lattice screening for excitons in halide perovskites, and generalize our findings by extending the Wannier model to include lattice polarization effects, clarifying the relevance of this effect for general classes of heteropolar semiconductors.

[1] Miyata et al, Nat. Phys. 11,582(2015)
[2] Umari et al, JPCL, 9,3,620(2018)