Preresonant Coherent IR-hyper-Raman Spectroscopy of FAPbBr3

Electron-phonon coupling is believed to influence many properties in lead halide perovskites (LHPs), including stability and photoefficency. Identifying the vibrational coordinates that compose excitonic potential energy surfaces in lead halide perovskites would prove instrumental for identifying the origin of these properties. Hyper difference frequency generation (HDFG) spectroscopy, which uses infrared and hyper-Raman transitions to measure coherent spectra and dynamics, has potential to resolve these couplings. As a first step toward the use of HDFG in identifying the vibrational coordinates and resolving these couplings, we measure the preresonant HDFG spectrum of FAPbBr3, a centrosymmetric 3D lead halide perovskite. The preresonant spectrum is found to be in agreement with FT-IR spectra and resolve A-site cation vibrations, suggesting that HDFG can be a useful tool for mapping out resonance trends that can inform on electron-phonon coupling, similar to those found in resonance Raman and hyper-Raman spectroscopy. This new approach to resolving vibrational spectra in materials systems is extendable to both centrosymmetric and noncentrosymmetric perovskites.