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arXiv · 2411.13727

Sign of the Gap Temperature Dependence in CsPb(Br,Cl)3 Nanocrystals Determined by Cs-Rattler Mediated Electron-Phonon Coupling

S. Fasahat·N. Fiuza-Maneiro·B. Schäfer·K. Xu·S. Gómez-Graña·M. I. Alonso·L. Polavarapu·A. R. Goñi
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Abstract

So far, the striking sign reversal in the near-ambient slope of the gap temperature dependence of colloidal CsPbCl3 perovskite nanocrystals (NCs) compared to its Br counterpart, remains unresolved. Pure bromide NCs exhibit a linear gap increase with increasing temperature, to which thermal expansion and electron-phonon interaction equally contribute. In contrast, the temperature slope for the chlorine compound gap is outspoken negative. By combining temperature and pressure-dependent photoluminescence on a series of CsPb(Br1-xClx)3 NCs, we unravel the origin of such inversion. Responsible is solely the electron-phonon interaction, undergoing a sudden change in sign and magnitude due to activation of an anomalous electron-phonon coupling mechanism linked to vibrational modes characterized by synchronous octahedral tilting and Cs rattling. This takes place in the shrunken orthorhombic NC lattice for Cl concentrations exceeding ca. 40%. We have thus clarified a puzzling result directly impacting the optoelectronic properties of lead halide perovskite NCs.

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S. Fasahat, N. Fiuza-Maneiro, B. Schäfer, K. Xu, S. Gómez-Graña, M. I. Alonso, L. Polavarapu, A. R. Goñi. 2024-11-20. Sign of the Gap Temperature Dependence in CsPb(Br,Cl)3 Nanocrystals Determined by Cs-Rattler Mediated Electron-Phonon Coupling. https://doi.org/10.1021/acs.jpclett.4c03491

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