Dynamic emission Stokes shift and liquid-like dielectric solvation of band edge carriers in lead-halide perovskites

• Published in: Nature communications 2019-03, Vol.10 (1), p.1175-8, Article 1175
• Main Authors: Guo, Yinsheng, Yaffe, Omer, Hull, Trevor D., Owen, Jonathan S., Reichman, David R., Brus, Louis E.
• Format: Article
• Language: English
• Subjects: 119/118; 140/125; 140/133; 639/301/119/1002; 639/301/119/995; 639/301/299/946; 639/4077/909/4101/4096; Anharmonicity; Crystal structure; Crystallinity; Crystals; Dielectric relaxation; Electronic spectra; Emission; Emissions; Humanities and Social Sciences; multidisciplinary; Optoelectronics; Perovskites; Photovoltaics; Science; Science (multidisciplinary); Semiconductors; Single crystals; Solvation; Temperature dependence; Vibrational spectra
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-019-09057-5

Lead-halide perovskites have emerged as promising materials for photovoltaic and optoelectronic applications. Their significantly anharmonic lattice motion, in contrast to conventional harmonic semiconductors, presents a conceptual challenge in understanding the genesis of their exceptional optoelectronic properties. Here we report a strongly temperature dependent luminescence Stokes shift in the electronic spectra of both hybrid and inorganic lead-bromide perovskite single crystals. This behavior stands in stark contrast to that exhibited by more conventional crystalline semiconductors. We correlate the electronic spectra with the anti-Stokes and Stokes Raman vibrational spectra. Dielectric solvation theories, originally developed for excited molecules dissolved in polar liquids, reproduce our experimental observations. Our approach, which invokes a classical Debye-like relaxation process, captures the dielectric response originating from the incipient anharmonicity of the LO phonon at about 20 meV (160 cm −1 ) in the lead-bromide framework. We reconcile this liquid-like model incorporating thermally-activated dielectric solvation with more standard solid-state theories of the emission Stokes shift in crystalline semiconductors. Lead halide perovskites have unique electronic properties that depend on the crystal’s anharmonicity. Dielectric solvation theories, developed for molecules dissolved in polar liquids, are shown here to reproduce the temperature behavior of carrier solvation in the electronic spectra, implying strongly anharmonic lattice dynamics.