Directly Unveiling the Energy Transfer Dynamics between Alq₃ Molecules and Si by Ultrafast Optical Pump-Probe Spectroscopy

The energy transfer (ET) between organic molecules and semiconductors is a crucial mechanism for enhancing the performance of semiconductor-based optoelectronic devices, but it remains undiscovered. Here, ultrafast optical pump-probe spectroscopy was utilized to directly reveal the ET between organic Alq₃ molecules and Si semiconductors. Ultrathin SiO₂ dielectric layers with a thickness of 3.2-10.8 nm were inserted between Alq₃ and Si to prevent charge transfer. By means of the ET from Alq₃ to Si, the SiO₂ thickness-dependent relaxation dynamics of photoexcited carriers in Si have been unambiguously observed on the transient reflectivity change (ΔR/R) spectra, especially for the relaxation process on a time scale of 200-350 ps. In addition, these findings also agree with the results of our calculation in a model of long-range dipole-dipole interactions, which provides critical information for developing future optoelectronic devices.