Directly Unveiling the Energy Transfer Dynamics between Alq<sub>3</sub> Molecules and Si by Ultrafast Optical Pump-Probe Spectroscopy.

Tai, Yu-Chan; Tzeng, Wen-Yen; Lin, Jhen-Dong; Kuo, Yi-Hou; Chen, Fu-Xiang Rikudo; Tu, Ruei-Jhe; Huang, Ming-Yang; Pai, Shyh-Shii et al. · Nano Lett · 2023

basic_science · Level V

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Abstract

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 Alq<sub>3</sub> molecules and Si semiconductors. Ultrathin SiO<sub>2</sub> dielectric layers with a thickness of 3.2-10.8 nm were inserted between Alq<sub>3</sub> and Si to prevent charge transfer. By means of the ET from Alq<sub>3</sub> to Si, the SiO<sub>2</sub> thickness-dependent relaxation dynamics of photoexcited carriers in Si have been unambiguously observed on the transient reflectivity change (Δ<i>R</i>/<i>R</i>) 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.