Photovoltaics

Photovoltaic effect

Heterojunction

Biology

Semiconductor

Band gap

Responsivity

Ecology

Materials science

Direct and indirect band gaps

Photodetector

Antimonide

Photocurrent

Photovoltaic system

Optoelectronics

Photodetection

Nano Letters

PN heterojunctions comprising layered van der Waals (vdW) semiconductors have been used to demonstrate current rectifiers, photodetectors, and photovoltaic devices. However, a direct or near-direct bandgap at the heterointerface that can significantly enhance optical generation, for high light absorbing few/multi-layer vdW materials, has not yet been shown. In this work, for the first time, few-layer group-6 transition metal dichalcogenide (TMD) $WSe_2$ is shown to form a sizeable (0.7 eV) near-direct bandgap with type-II band alignment at its interface with the group-7 TMD $ReS_2$ through density functional theory calculations. Further, the type-II alignment and photogeneration across the interlayer bandgap have been experimentally confirmed through micro-photoluminescence and IR photodetection measurements, respectively. High optical absorption in few-layer flakes, large conduction and valence band offsets for efficient electron-hole separation and stacking of light facing, direct bandgap $ReS_2$ on top of gate tunable $WSe_2$ are shown to result in excellent and tunable photodetection as well as photovoltaic performance through flake thickness dependent optoelectronic measurements. Few-layer flakes demonstrate ultrafast response time (5 $\mu$s) at high responsivity (3 A/W) and large photocurrent generation and responsivity enhancement at the heterostructure overlap region (10-100X) for 532 nm laser illumination. Large open-circuit voltage of 0.64 V and short-circuit current of 2.6 $\mu$A enables high output electrical power. Finally, long term air-stability and a facile single contact metal fabrication process makes the multi-functional few-layer $WSe_2$/$ReS_2$ heterostructure diode technologically promising for next-generation optoelectronic applications.

Near-Direct Bandgap WSe<sub>2</sub>/ReS<sub>2</sub> Type-II pn Heterojunction for Enhanced Ultrafast Photodetection and High-Performance Photovoltaics

Near-Direct Bandgap WSe2/ReS2 Type-II pn Heterojunction for Enhanced Ultrafast Photodetection and High-Performance Photovoltaics

Near-Direct Bandgap WSe₂/ReS₂ Type-II pn Heterojunction for Enhanced Ultrafast Photodetection and High-Performance Photovoltaics