Defect-Engineered Reduction of the Carrier Multiplication Threshold in Monolayer WS<sub>2</sub> to 1.6<i>E</i><sub>g</sub>.
basic_science · Level V
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- Record sourced from PubMed, PMID 41203562.
- Also identified by DOI 10.1021/acsnano.5c15291.
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Abstract
Carrier multiplication (CM), a process generating two or more electron-hole pairs after absorbing one high-energy photon, holds great potential for breaking the Shockley-Queisser limit in photovoltaics. However, conventional CM in semiconductors is constrained by a high threshold (>2<i>E</i><sub>g</sub>), leaving the excess energy of sub-2<i>E</i><sub>g</sub> high-energy photons unutilized. Here, using transient-absorption spectroscopy, we report the systematic experimental realization of a low CM threshold of 1.6<i>E</i><sub>g</sub> in monolayer WS<sub>2</sub> by leveraging strong electron-phonon coupling (EPC) through engineering high-symmetric disulfur vacancies. Steady-state spectroscopic measurements (photoluminescence and Raman) and density functional theory calculations reveal that the reduced CM threshold arises from efficient phonon-assisted upconversion that enables the transition from sulfur divacancy-induced in-gap states to the conduction band minimum of WS<sub>2</sub> due to strong EPC. Our work enables a distinct strategy for reducing the CM threshold, which contributes directly to the pursuit of high-efficiency photovoltaics and next-generation optoelectronic technologies.