Yuan Rongfeng, Roberts Trevor D, Brinn Rafaela M, Choi Alexander A, Park Ha H, Yan Chang, Ondry Justin C, Khorasani Siamak, Masiello David J, Xu Ke, Alivisatos A Paul, Ginsberg Naomi S
Department of Chemistry, University of California Berkeley, Berkeley, CA 94720, USA.
Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA.
Sci Adv. 2023 Oct 20;9(42):eadh2410. doi: 10.1126/sciadv.adh2410.
Quantum dot (QD) solids are promising optoelectronic materials; further advancing their device functionality requires understanding their energy transport mechanisms. The commonly invoked near-field Förster resonance energy transfer (FRET) theory often underestimates the exciton hopping rate in QD solids, yet no consensus exists on the underlying cause. In response, we use time-resolved ultrafast stimulated emission depletion (STED) microscopy, an ultrafast transformation of STED to spatiotemporally resolve exciton diffusion in tellurium-doped cadmium selenide-core/cadmium sulfide-shell QD superlattices. We measure the concomitant time-resolved exciton energy decay due to excitons sampling a heterogeneous energetic landscape within the superlattice. The heterogeneity is quantified by single-particle emission spectroscopy. This powerful multimodal set of observables provides sufficient constraints on a kinetic Monte Carlo simulation of exciton transport to elucidate a composite transport mechanism that includes both near-field FRET and previously neglected far-field emission/reabsorption contributions. Uncovering this mechanism offers a much-needed unified framework in which to characterize transport in QD solids and additional principles for device design.
量子点（QD）固体是很有前景的光电子材料；要进一步提升其器件功能，需要了解其能量传输机制。通常援引的近场Förster共振能量转移（FRET）理论常常低估了量子点固体中的激子跳跃速率，但对于其根本原因尚无定论。对此，我们使用时间分辨超快受激发射损耗（STED）显微镜，这是一种将STED进行超快变换以在时空上分辨碲掺杂的硒化镉核/硫化镉壳量子点超晶格中激子扩散的方法。我们测量了由于激子在超晶格内采样异质能量格局而伴随产生的时间分辨激子能量衰减。这种异质性通过单粒子发射光谱进行量化。这组强大的多模态可观测数据为激子输运动力学蒙特卡罗模拟提供了足够的约束，以阐明一种复合传输机制，该机制包括近场FRET和先前被忽视的远场发射/再吸收贡献。揭示这一机制提供了一个急需的统一框架，用于表征量子点固体中的传输以及器件设计的其他原理。
