29,549 research outputs found
High Photovoltaic Quantum Efficiency in Ultrathin van der Waals Heterostructures
We report experimental measurements for ultrathin (< 15 nm) van der Waals
heterostructures exhibiting external quantum efficiencies exceeding 50%, and
show that these structures can achieve experimental absorbance > 90%. By
coupling electromagnetic simulations and experimental measurements, we show
that pn WSe2/MoS2 heterojunctions with vertical carrier collection can have
internal photocarrier collection efficiencies exceeding 70%.Comment: ACS Nano, 2017. Manuscript (25 pages, 7 figures) plus supporting
information (7 pages, 4 figures
Van der Waals Materials for Atomically-Thin Photovoltaics: Promise and Outlook
Two-dimensional (2D) semiconductors provide a unique opportunity for
optoelectronics due to their layered atomic structure, electronic and optical
properties. To date, a majority of the application-oriented research in this
field has been focused on field-effect electronics as well as photodetectors
and light emitting diodes. Here we present a perspective on the use of 2D
semiconductors for photovoltaic applications. We discuss photonic device
designs that enable light trapping in nanometer-thickness absorber layers, and
we also outline schemes for efficient carrier transport and collection. We
further provide theoretical estimates of efficiency indicating that 2D
semiconductors can indeed be competitive with and complementary to conventional
photovoltaics, based on favorable energy bandgap, absorption, external
radiative efficiency, along with recent experimental demonstrations. Photonic
and electronic design of 2D semiconductor photovoltaics represents a new
direction for realizing ultrathin, efficient solar cells with applications
ranging from conventional power generation to portable and ultralight solar
power.Comment: 4 figure
Mobility engineering and metal-insulator transition in monolayer MoS2
Two-dimensional (2D) materials are a new class of materials with interesting
physical properties and ranging from nanoelectronics to sensing and photonics.
In addition to graphene, the most studied 2D material, monolayers of other
layered materials such as semiconducting dichalcogenides MoS2 or WSe2 are
gaining in importance as promising insulators and channel materials for
field-effect transistors (FETs). The presence of a direct band gap in monolayer
MoS2 due to quantum mechanical confinement, allows room-temperature
field-effect transistors with an on/off ratio exceeding 108. The presence of
high-k dielectrics in these devices enhanced their mobility, but the mechanisms
are not well understood. Here, we report on electrical transport measurements
on MoS2 FETs in different dielectric configurations. Mobility dependence on
temperature shows clear evidence of the strong suppression of charge impurity
scattering in dual-gate devices with a top-gate dielectric together with phonon
scattering that shows a weaker than expected temperature dependence. High
levels of doping achieved in dual-gate devices also allow the observation of a
metal-insulator transition in monolayer MoS2. Our work opens up the way to
further improvements in 2D semiconductor performance and introduces MoS2 as an
interesting system for studying correlation effects in mesoscopic systems.Comment: Submitted January 11, 201
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