2D monolayer molybdenum disulphide (MoS2) has been the focus of intense research due to its direct bandgap compared with the indirect bandgap of its bulk counterpart; however its photoluminescence (PL) intensity is limited due to its low absorption efficiency.
Control over photophysical
and chemical properties of two-dimensional
(2D) transition metal dichalcogenides (TMDs) is the key to advance
their applications in next-generation optoelectronics. Although chemical
doping and surface modification with plasmonic metals have been reported
to tune the photophysical and catalytic properties of 2D TMDs, there
have been few reports of tuning optical properties using dynamic electrochemical
control of electrode potential. Herein, we report (1) the photoluminescence
(PL) enhancement and red-shift in the PL spectrum of 2D MoS2, synthesized by chemical vapor deposition and subsequent transfer
onto an indium tin oxide electrode, upon electrochemical anodization
and (2) spatial heterogeneities in its photoelectrochemical (PEC)
activities. Spectroelectrochemistry shows that positive electrochemical
bias causes an initial ten-fold increase in the PL intensity followed
by a quick decrease in the enhancement. The PL enhancement and spectrum
red-shift are associated with the decrease in nonradiative decay rates
of excitons formed upon electrochemical anodization of 2D MoS2. Additionally, scanning electrochemical cell microscopy (SECCM)
study shows that the 2D MoS2 crystal is spatially sensitive
to PEC oxidation at positive potentials. SECCM also shows a photocurrent
increase caused by spatially heterogeneous edge-type defect sites
of the crystal.
Two-dimensional molybdenum disulfide (MoS 2) has substantial potential as a semiconducting material for devices. However, it is commonly prepared by mechanical exfoliation, which limits flake size to only a few micrometers, which is not sufficient for processes such as photolithography and circuit patterning. Chemical vapor deposition (CVD) has thus become a mainstream fabrication technique to achieve large-area MoS 2. However, reports of conventional photolithographic patterning of large-area 2D MoS 2-based devices with high mobilities and low switching voltages are rare. Here we fabricate CVD-grown large-area MoS 2 fieldeffect transistors (FETs) by photolithography and demonstrate their potential as switching and driving FETs for pixels in analog organic light-emitting diode (OLED) displays. We spin-coat an ultrathin hydrophobic polystyrene layer on an Al 2 O 3 dielectric, so that the uniformity of threshold voltage (V th) of the FETs might be improved. Our MoS 2 FETs show a high linear mobility of approximately 10 cm 2 V −1 s −1 , due to a large grain size around 60 μm, and a high ON/OFF current ratio of 10 8. Dynamic switching of blue and green OLED pixels is shown at~5 V, demonstrating their application potential.
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