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Probe Type II Band Alignment in One-Dimensional Van Der Waals Heterostructures Using First-Principles Calculations
Published on: October 12, 2019
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Molecular-Scale Characterization of Photoinduced Charge Separation in Mixed-Dimensional InSe-Organic van der Waals
Shaowei Li1, Chengmei Zhong1,2, Alex Henning1
1Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208-3108, United States.
ACS Nano
|February 21, 2020
Summary
Researchers studied layered indium selenide (InSe) and organic molecules to create new electronic devices. They found that combining InSe with C70 molecules creates a type-II heterojunction, enabling efficient charge separation for optoelectronic applications.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Nanotechnology
Background:
- Layered indium selenide (InSe) is a promising 2D semiconductor for electronics.
- Mixed-dimensional heterostructures with organic molecules can expand InSe's optoelectronic uses.
Purpose of the Study:
- Investigate photoinduced charge separation in InSe-organic molecule heterostructures.
- Determine the nature of heterojunctions formed between InSe and C70 or C8-BTBT.
Main Methods:
- Spatially resolved scanning tunneling microscopy (STM) with laser illumination.
- Laser-excited scanning tunneling spectroscopy (LE-STS).
- Photoluminescence spectroscopy and Kelvin probe force microscopy (KPFM).
- Computational methods including density functional theory (DFT).
Main Results:
- InSe forms type-II heterojunctions with C70 and type-I with C8-BTBT.
- Optical illumination decreased the lowest unoccupied molecular orbital (LUMO) of C70 by ~0.25 eV.
- Electron transfer in InSe-C70 heterojunctions induced a photovoltage matching spectral shifts.
- Band alignment in heterostructures deviates from predictions based on isolated components.
Conclusions:
- Charge transfer and dielectric screening govern band alignment in InSe-organic heterostructures.
- This work provides a methodology for studying nanoscale charge transfer in photoactive systems.
- Mixed-dimensional heterostructures offer tunable optoelectronic properties.
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