Charge Transfer Effects on Resonance-Enhanced Raman Scattering for Molecules Adsorbed on Single-Crystalline Perovskite

Single-crystalline hybrid perovskites have important photoelectronic properties for advanced semiconductor devices, such as solar cells and photodetectors. However, neither the surface-enhanced Raman scattering (SERS) property nor the correlation between SERS and photoelectronic properties for single-crystalline perovskites have ever been studied. Here, for the first time, we observed a 105 enhancement in SERS for 4-mercaptopyridine (MPY) adsorbed on a methylamine lead chlorine (MAPbCl3) single crystal. Compared to the Raman spectrum of bulk MPY molecules, the b2 mode of the MPY molecule was selectively enhanced. This is attributed to the charge transfer (CT) resonance mechanism at the interface between the single crystal and the adsorbed molecules, which benefit from the Herzberg–Teller contribution. UV–vis spectra demonstrated that the modification with the MPY molecules leads to the formation of a new interfacial transition state, which matches the excitation laser photon energy and results in a CT resonance process under 532 nm laser excitation. The MPY-modified MAPbCl3 single crystal was further applied to a photoelectronic device, and the device I–V curve was collected under 532 nm laser irradiation. The results indicate that the MPY-modified MAPbCl3 shows a clear photoelectronic response to the 532 nm light. This study establishes a correlation between the CT resonance-enhanced Raman and the photoelectronic responses of perovskite materials and provides guidance for future molecule-sensitized perovskite photoelectronic device studies.