Electron-phonon coupling in two-dimensional Ruddlesden-Popper hybrid perovskites

Two-dimensional lead halide perovskites are considered low-cost and relatively stable materials for high-efficiency photovoltaic applications. Photoexcitation of lead halide perovskite materials leads to the generation of charge carriers. Understanding the charge carrier dynamics, especially at the early stage of their generation, is crucial for improving photovoltaic efficiency. Among the various dynamic charge carrier features, investigation of the interaction between the carriers and lattice modes provides crucial information about the behavior of the photoexcited carriers. Effective interaction between the charge carriers and lattice modes often produces polarons, which are considered to influence the charge carrier transport properties and thereby the photovoltaic efficiencies. In this review, we discuss the recent developments in various methods, including temperature-dependent photoluminescence (PL) spectroscopy and femtosecond transient absorption (fs-TA) spectroscopy, for the detection of electron-phonon coupling in two-dimensional (2D) Ruddlesden-Popper (RP) perovskites. While temperature-dependent PL measurements provide an easy and convenient way of detecting electron-phonon coupling phenomena, fs-TA spectroscopy could deliver a more comprehensive understanding of the processes. We further discuss how the electron-phonon coupling affects various important properties in 2D halide perovskite films, such as the band gap modulation, PL behavior, self-trapped exciton formation and hot carrier cooling rates which are crucial for the study of perovskite optoelectronics.