Abstract
Structural defects vary the optoelectronic properties of monolayer transition metal dichalcogenides, leading to concerted efforts to control defect type and density via materials growth or postgrowth passivation. Here, we explore a simple chemical treatment that allows on–off switching of low-lying, defect-localized exciton states, leading to tunable emission properties. Using steady-state and ultrafast optical spectroscopy, supported by ab initio calculations, we show that passivation of sulfur vacancy defects, which act as exciton traps in monolayer MoS2 and WS2, allows for controllable and improved mobilities and an increase in photoluminescence up to 275-fold, more than twice the value achieved by other chemical treatments. Our findings suggest a route for simple and rational defect engineering strategies for tunable and switchable electronic and excitonic properties through passivation.
Highlights
Structural defects vary the optoelectronic properties of monolayer transition metal dichalcogenides, leading to concerted efforts to control defect type and density via materials growth or postgrowth passivation
Monolayer TMDCs possess a direct bandgap, optical excitations in the visible range, and very high absorption coefficients.[1−3] the photoluminescence (PL) arising from exciton radiative recombination typically shows low PL quantum yields (PLQYs); in monolayer MoS2 and WS2, prepared via exfoliation or chemical vapor deposition, the PLQY has been measured to be below 1% for MoS2 and only slightly higher for WS2.1,4,5 This low PLQY is attributed to the presence of defects in these materials,[6−9] which quench photoluminescence and limit carrier mobilities.[5,6,10−12] A systematic understanding of the nature of defects and the corresponding development of appropriate defect passivation strategies is greatly desired and is expected to improve device applications ranging from light-emitting diodes and photovoltaics to quantum emitters and future quantum information devices
We study the nature of defect states created upon various chemical passivation methods through steady-state and ultrafast spectroscopy, supported by ab initio GW and Bethe Salpeter equation (GW-BSE) calculations.[48−51] We experimentally demonstrate the formation of subgap absorption features that are consistent with theoretically predicted energies for confined excitons associated with sulfur vacancies
Summary
Structural defects vary the optoelectronic properties of monolayer transition metal dichalcogenides, leading to concerted efforts to control defect type and density via materials growth or postgrowth passivation. We explore the effect of defect passivation on PL yield and exciton lifetimes in monolayer TMDCs. We study the nature of defect states created upon various chemical passivation methods through steady-state and ultrafast spectroscopy, supported by ab initio GW and Bethe Salpeter equation (GW-BSE) calculations.[48−51] We experimentally demonstrate the formation of subgap absorption features that are consistent with theoretically predicted energies for confined excitons associated with sulfur vacancies. We study the nature of defect states created upon various chemical passivation methods through steady-state and ultrafast spectroscopy, supported by ab initio GW and Bethe Salpeter equation (GW-BSE) calculations.[48−51] We experimentally demonstrate the formation of subgap absorption features that are consistent with theoretically predicted energies for confined excitons associated with sulfur vacancies These subgap states act as traps and lengthen PL lifetimes while limiting PL yields and carrier mobilities. The generalizability of this protocol, which can be performed with a number of chemical agents, enhances the optoelectronic properties of TMDCs through passivation, but can be used to functionalize these materials and tune their PL properties
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