Photovoltaic effect in few-layer black phosphorus PN junctions defined by local electrostatic gating

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Conventional solar cells rely on PN junctions formed by ionic dopants.
• Electrically tunable PN junctions in 2D semiconductors are challenging due to lack of ambipolar transport.
• Few-layer black phosphorus (b-P) exhibits ambipolar transport, high mobility, and a direct bandgap.

Purpose of the Study:

• To demonstrate the feasibility of creating gate-defined PN junctions in few-layer black phosphorus (b-P).
• To investigate the photovoltaic properties of these engineered PN junctions under illumination.
• To assess the potential of b-P for near-infrared energy harvesting.

Main Methods:

• Fabrication of few-layer black phosphorus field-effect transistors using split gates and hexagonal boron nitride dielectric.
• Electrostatic control of local charge carrier type and density.
• Illumination of the gate-defined PN junction to measure photocurrent and open-circuit voltage.

Main Results:

• Successful demonstration of electrostatic control over carrier type and density in b-P devices.
• Observation of zero-bias photocurrents and significant open-circuit voltages, confirming the photovoltaic effect.
• Power generation observed for wavelengths up to 940 nm due to b-P's small bandgap.

Conclusions:

• Few-layer black phosphorus can be engineered into electrically tunable PN junctions for photovoltaic applications.
• The observed photovoltaic effect in b-P devices opens avenues for near-infrared energy harvesting.
• This work highlights the potential of 2D materials beyond conventional silicon-based photovoltaics.