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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 (>2Eg), leaving the excess energy of sub-2Eg high-energy photons unutilized. Here, using transient-absorption spectroscopy, we report the systematic experimental realization of a low CM threshold of 1.6Eg in monolayer WS2 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 WS2 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.
Li et al. (Fri,) studied this question.