Wang Lei, Yang Gaoyuan, Zhang Boyu, Zhang Xin, Liu Dezheng, Liang Ying, Liang Guijie
Opt Express. 2022 Dec 19;30(26):47440-47451. doi: 10.1364/OE.478579.
Triplet generation by quantum dots (QDs)-sensitized molecules emerges great potential in many applications. However, the mechanism of triplet energy transfer (TET) is still fuzzy especially due to the complicated energy level alignment of QDs and molecules or trap states in QDs. Here, CdSe QDs and 5-tetracene carboxylic acid (TCA) molecules are selected as the triplet donor and acceptor, respectively, to form a TET system. By tuning the band gap of CdSe, the CdSe-TCA complex is exactly designed to present a Type-II like alignment of relative energetics. Coupling the transient absorption and time-resolved fluorescence spectra, all carrier dynamics is distinctly elucidated. Quantitative analysis demonstrates that hole transfer persisting for ∼ 2 ps outcompetes all other carrier dynamics such as electron trapping (∼100 ps level), charge recombination (∼ 5 ns) and the so-called "back transfer charge recombination" (∼50 ns), and thus leads to a hole-transfer-mediated TET process. The low TET yield (∼34.0%) ascribed to electron behavior can be further improved if electron trapping and charge recombination are efficiently suppressed. The observation on distinguishable carrier dynamics attributed to legitimate design of energy level alignment facilitates a better understanding of the TET mechanism from QDs to molecules as well as further development of photoelectronic devices based on such TET systems.
量子点（QD）敏化分子产生三线态在许多应用中展现出巨大潜力。然而，三线态能量转移（TET）的机制仍然模糊，特别是由于量子点与分子复杂的能级排列或量子点中的陷阱态。在此，分别选择CdSe量子点和5-四苯二甲酸（TCA）分子作为三线态供体和受体，形成一个TET系统。通过调节CdSe的带隙，精确设计CdSe-TCA复合物以呈现类似II型的相对能量排列。结合瞬态吸收和时间分辨荧光光谱，清晰地阐明了所有载流子动力学。定量分析表明，持续约2皮秒的空穴转移胜过所有其他载流子动力学过程，如电子俘获（约100皮秒量级）、电荷复合（约5纳秒）和所谓的“反向转移电荷复合”（约50纳秒），从而导致一个空穴转移介导的TET过程。如果能有效抑制电子俘获和电荷复合，归因于电子行为的低TET产率（约34.0%）可以进一步提高。对可区分载流子动力学的观察归因于能级排列的合理设计，这有助于更好地理解从量子点到分子的TET机制以及基于此类TET系统的光电器件的进一步发展。
