期刊
ACS NANO
卷 14, 期 3, 页码 3509-3518出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.9b09661
关键词
indium selenide; fullerene; scanning tunneling microscopy; photoluminescence spectroscopy; transient absorption spectroscopy; Kelvin probe force microscopy
类别
资金
- Materials Research Science and Engineering Center (MRSEC) of Northwestern University [NSF DMR-1720139]
- Center for Light Energy Activated Redox Processes (LEAP), an Energy Frontier Research Center - U.S. Department of Energy, Office of Science, Basic Energy Sciences [DE-SC0001059]
- Czech Science Foundation (GACR) [17-11456S]
- Neuron Foundation
- Advanced Functional Nanorobots Program (EFRR) [CZ.02.1.01/0.0/0.0/15_003/0000444]
- DFG [HE-7999/1-1]
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357]
Layered indium selenide (InSe) is an emerging two-dimensional semiconductor that has shown significant promise for high-performance transistors and photodetectors. The range of optoelectronic applications for InSe can potentially be broadened by forming mixed-dimensional van der Waals heterostructures with zero-dimensional molecular systems that are widely employed in organic electronics and photovoltaics. Here, we report the spatially resolved investigation of photoinduced charge separation between InSe and two molecules (C-70 and C-8-BTBT) using scanning tunneling microscopy combined with laser illumination. We experimentally and computationally show that InSe forms type-II and ype-I heterojunctions with C-70 and C-8-BTBT, respectively, due to an interplay of charge transfer and dielectric screening at the interface. Laser-excited scanning tunneling spectroscopy reveals a similar to 0.25 eV decrease in the energy of the lowest unoccupied molecular orbital of C-70 with optical illumination. Furthermore, photoluminescence spectroscopy and Kelvin probe force microscopy indicate that electron transfer from InSe to C-70 in the type-II heterojunction induces a photovoltage that quantitatively matches the observed downshift in the tunneling spectra. In contrast, no significant changes are observed upon optical illumination in the type-I heterojunction formed between InSe and C-8-BTBT. Density functional theory calculations further show that, despite the weak coupling between the molecular species and InSe, the band alignment of these mixed-dimensional heterostructures strongly differs from the one suggested by the ionization potential and electronic affinities of the isolated components. Self-energy-corrected density functional theory indicates that these effects are the result of the combination of charge redistribution at the interface and heterogeneous dielectric screening of the electron-electron interactions in the heterostructure. In addition to providing specific insight for mixed-dimensional InSe-organic van der Waals heterostructures, this work establishes a general experimental methodology for studying localized charge transfer at the molecular scale that is applicable to other photoactive nanoscale systems.
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