Enhanced Optical Absorption and Slowed Light of Reduced-Dimensional CsPbBr₃ Nanowire Crystal by Exciton–Polariton

Abstract

Metallic halide perovskites are promising for low-cost, low-consumption, flexible optoelectronic devices. However, research is lacking on light propagation and dielectric behaviors as fundamental properties for optoelectronic perovskite applications, particularly the mechanism supporting a strong light-matter interaction and the different properties of low-dimensional structures from their bulk counterparts. We use spatially resolved photoluminescence (SRPL) spectroscopy to explore light propagation and measure the refractive index of CsPbBr₃ nanowires (NWs). Owing to strong exciton-photon interactions, light is guided as an exciton-polariton inside the NWs at room temperature. Remarkable spatial dispersion is confirmed, in which both the real and imaginary parts of the refractive index increase dramatically approaching exciton resonance, thus slowing light and enhancing absorption, respectively. Reducing the NWs dimension increases exciton-photon coupling and the exciton fraction, increasing the light absorption coefficient and group index 5- and 3-fold, respectively, relative to those of bulk films and slowing the light group velocity by ∼74%. Furthermore, dispersive absorption induces an energy redshift to the propagating PL at 4.1-5.5 meV μm^-1 until the bottleneck region. These findings clarify light-matter interaction in confined perovskite structures to improve their optoelectronic device performance.