Tuning Interface Barrier in 2D BP/ReSe2 Heterojunctions in Control of Optoelectronic Performances and Energy Conversion Efficiencies

The two-dimensional (2D) van der Waals hetero-structure has drawn much attention due to its native built-in barrier benefiting the applications to electronic and optoelectronic devices. There are several reports but the relation between the built-in barrier and optoelectrical properties has not been unveiled yet. Here we stack few-layer black phosphorus (BP) and ReSe2 flakes together at the microscale and make back- gate-tunable BP/ReSe2 heterojunction devices. The rectification manner of the heterojunction is investigated and, interestingly, the current-voltage (I-V) curves do not follow the common diode model of the Shockley equation. In contrast, the I-V curves are well described by models of the direct tunneling, the Fowler-Nordheim (F-N) tunneling, and the space-charge-limited current in different voltage ranges. The interface built-in barrier of the BP/ReSe2 heterojunction is determined by data analysis according to the F-N tunneling model. In addition, photoresponsivity and photovoltaic effects are investigated with laser light shining on the heterojunction. Comparing the optoelectrical properties and the rectified I-V demeanors, we discover the essential role that the interface built-in barrier plays on the rectification, the photocurrent, and the photovoltaic cell. This work demonstrates as well the highest external quantum efficiency and energy conversion efficiency for heterojunctions based on few-layer 2D materials.