Fan Kezhou, Sergeeva Kseniia A, Sergeev Aleksandr A, Zhang Lu, Chan Christopher C S, Li Zhuo, Zhong Xiaoyan, Kershaw Stephen V, Liu Junwei, Rogach Andrey L, Wong Kam Sing
Department of Physics and William Mong Institute of Nano Science and Technology, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong S.A.R., P. R. China.
Department of Materials Science and Engineering, City University of Hong Kong, Kowloon, Hong Kong S.A.R., P. R. China.
ACS Nano. 2024 Jul 9;18(27):18011-18021. doi: 10.1021/acsnano.4c05061. Epub 2024 Jun 27.
Rapid hot-carrier/exciton cooling constitutes a major loss channel for photovoltaic efficiency. How to decelerate the hot-carrier/exciton relaxation remains a crux for achieving high-performance photovoltaic devices. Here, we demonstrate slow hot-exciton cooling that can be extended to hundreds of picoseconds in colloidal HgTe quantum dots (QDs). The energy loss rate is 1 order of magnitude smaller than bulk inorganic semiconductors, mediated by phonon bottleneck and interband biexciton Auger recombination (BAR) effects, which are both augmented at reduced QD sizes. The two effects are competitive with the emergence of multiple exciton generation. Intriguingly, BAR dominates even under low excitation fluences with a decrease in interparticle distance. Both experimental evidence and numerical evidence reveal that such efficient BAR derives from the tunneling-mediated interparticle excitonic coupling induced by wave function overlap between neighboring HgTe QDs in films. Thus, our study unveils the potential for realizing efficient hot-carrier/exciton solar cells based on HgTe QDs. Fundamentally, we reveal that the delocalized nature of quantum-confined wave function intensifies BAR. The interparticle excitonic coupling may cast light on the development of next-generation photoelectronic materials, which can retain the size-tunable confinement of colloidal semiconductor QDs while simultaneously maintaining high mobilities and conductivities typical for bulk semiconductor materials.
快速热载流子/激子冷却构成了光伏效率的一个主要损失通道。如何减缓热载流子/激子弛豫仍然是实现高性能光伏器件的关键所在。在此，我们展示了在胶体HgTe量子点（QD）中可延长至数百皮秒的缓慢热激子冷却。能量损失率比体相无机半导体小1个数量级，这是由声子瓶颈和带间双激子俄歇复合（BAR）效应介导的，在减小的量子点尺寸下这两种效应都会增强。这两种效应与多激子产生的出现相互竞争。有趣的是，即使在低激发通量下且粒子间距离减小，BAR仍占主导。实验证据和数值证据均表明，这种高效的BAR源于薄膜中相邻HgTe量子点之间波函数重叠所诱导的隧穿介导的粒子间激子耦合。因此，我们的研究揭示了基于HgTe量子点实现高效热载流子/激子太阳能电池的潜力。从根本上说，我们揭示了量子限域波函数的离域性质增强了BAR。粒子间激子耦合可能会为下一代光电子材料的发展提供启示，这类材料可以保留胶体半导体量子点的尺寸可调限域特性，同时保持体相半导体材料典型的高迁移率和电导率。
