Differing vibrational properties of halide and chalcogenide perovskite semiconductors and impact on optoelectronic performance

We report a comparative study of temperature-dependent photoluminescence and structural dynamics of two perovskite semiconductors, the chalcogenide ${\mathrm{BaZrS}}_3$ and the halide $\mathrm{Cs}\mathrm{Pb}{\mathrm{Br}}_3$. These materials have similar crystal structures and direct band gaps, but we find that they have quite distinct optoelectronic and vibrational properties. Both materials exhibit thermally activated nonradiative recombination, but the nonradiative recombination rate in ${\mathrm{BaZrS}}_3$ is four orders of magnitude faster than in $\mathrm{Cs}\mathrm{Pb}{\mathrm{Br}}_3$, for the crystals studied here. Raman spectroscopy reveals that the effects of phonon anharmonicity are far more pronounced in $\mathrm{Cs}\mathrm{Pb}{\mathrm{Br}}_3$ than in ${\mathrm{BaZrS}}_3$. Further, although both materials feature a large dielectric response due to low-energy polar optical phonons, the phonons in $\mathrm{Cs}\mathrm{Pb}{\mathrm{Br}}_3$ are substantially lower in energy than in ${\mathrm{BaZrS}}_3$. Our results suggest that electron-phonon coupling in ${\mathrm{BaZrS}}_3$ is more effective at nonradiative recombination than in $\mathrm{Cs}\mathrm{Pb}{\mathrm{Br}}_3$ and that ${\mathrm{BaZrS}}_3$ may also have a substantially higher concentration of nonradiative recombination centers than $\mathrm{Cs}\mathrm{Pb}{\mathrm{Br}}_3$. The low defect concentration in $\mathrm{Cs}\mathrm{Pb}{\mathrm{Br}}_3$ may be related to the ease of lattice reconfiguration, typified by anharmonic bonding. It remains to be seen to what extent these differences are inherent to the chalcogenide and halide perovskites and to what extent they can be affected by materials processing.