Light-Induced Electronic Band Realignment at the Metal Halide Perovskite/Monolayer MoS₂ Heterojunction

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Van der Waals (vdW) heterojunctions, combining 2D transition metal dichalcogenides (TMDCs) with metal halide perovskites, show promise for advanced optoelectronics.
• Accurate determination of electronic energy level alignment at these interfaces is critical but experimentally challenging.

Purpose of the Study:

• To experimentally determine the energy level alignment at a perovskite/monolayer molybdenum disulfide (ML-MoS2) vdW heterojunction.
• To investigate the behavior of this alignment under operational conditions, specifically 1 sun illumination.

Main Methods:

• Utilized argon cluster sputtering for effective surface cleaning of the perovskite/ML-MoS2 stack.
• Employed ultraviolet and X-ray photoelectron spectroscopy (XPS) for direct band alignment determination.
• Performed microscopic photoluminescence (PL) measurements to confirm charge transfer.

Main Results:

• Revealed a type-II band alignment at the perovskite/ML-MoS2 interface.
• Observed a significant shift (up to 0.25 eV) in MoS2 energy levels relative to perovskite under illumination, termed energy level realignment.
• Demonstrated efficient charge transfer and perovskite PL quenching, confirming the type-II heterojunction characteristics.

Conclusions:

• The study demonstrates a dynamic, or "living," heterojunction energy landscape.
• The observed energy level realignment under illumination offers new strategies for engineering perovskite/TMDCs vdW heterojunctions for enhanced optoelectronic device performance.