期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 141, 期 26, 页码 10451-10461出版社
AMER CHEMICAL SOC
DOI: 10.1021/jacs.9b04663
关键词
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资金
- U.S. Department of Energy, Office of Science, Basic Energy Sciences [DE-SC0002120]
- U.S. Department of Energy (DOE) [DE-SC0002120] Funding Source: U.S. Department of Energy (DOE)
Nonradiative charge-carrier recombination in transition-metal dichalcogenide (TMD) monolayers severely limits their use in solar energy conversion technologies. Because defects serve as recombination sites, developing a quantitative description of charge-carrier dynamics in defective TMD monolayers can shed light on recombination mechanisms. Herein we report a first-principles investigation of charge-carrier dynamics in pristine and defective WSe2 monolayers with three of the most probable defects, namely, Se vacancies, W vacancies, and Sew antisites. We predict that Se vacancies slow down recombination by nearly an order of magnitude relative to defect-free samples by breaking the monolayer's symmetry and thereby reducing the spectral intensity of the A(1g) phonon mode that promotes recombination in the pristine monolayer. By contrast, we find W vacancies accelerate recombination by more than an order of magnitude, with half of the recombination events bypassing charge traps. The subsequent dynamics feature both charge trapping and charge-trap-assisted recombination. Although Sew antisites also slightly accelerate recombination, the predicted mechanism is different from the W vacancy case. First, a shallow energy level traps a photoexcited electron. Then, both shallow- and deep-trap-assisted recombination can occur simultaneously. Accelerated recombination arises for W vacancies and Sew antisites because they introduce new phonon modes that strongly couple to electron and hole dynamics. This work thus provides a detailed understanding of the mechanisms behind charge-carrier recombination in WSe2 monolayers with distinct defects. Thus, materials engineering, particularly to avoid W vacancies, could advance this technology. The insights derived are important for future design of high-performance photoactive devices based on WSe2 monolayers.
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