Engineering Relaxation-Paths of C-Exciton for Constructing Band Nesting Bypass in WS 2 Monolayer

作者：Jiying Feng, Yuanzheng Li, Jixiu Li, Qiushi Feng, Wei Xin, Weizhen Liu, Haiyang Xu, Yichun Liu · 发表于：Nano Letters · 年份：2022 · DOI：10.1021/acs.nanolett.2c00509 · 被引用次数：22 · 研究领域：2D Materials and Applications、Perovskite Materials and Applications、Advanced biosensing and bioanalysis techniques

Transition-metal dichalcogenides exhibit strong photon absorption characteristics in the band nesting region (denoted as C-exciton) due to intrinsic van Hove singularities despite being atomically thin. However, because of unique parallel band structure and ineluctably unfavorable recombination process, only a small fraction of the hot carriers from C-excitons are converted into optically active band-edge excitons via inherent relaxation-paths. The resultant photoluminescence quantum yield (PLQY) is severely suppressed for the resonant excitation of C-exciton. To overcome this limitation, we have designed double type-I band alignments to construct a band nesting bypass in a monolayer WS 2 /CdS quantum dot heterostructure for cooling the C-excitons. Transient optical measurements confirmed that the hot carriers from the C-excitons were effectively transferred from WS 2 to CdS with an efficiency of 50% and subsequently back to the WS 2 band-edge to form A-excitons over an ultrafast subpicosecond time scale, accompanied by a record high PLQY of ∼11.1% for near-resonance C-exciton excitation.