| Autor: |
Almadori, Yann, Bendiab, Nedjma, Grévin, Benjamin |
| Zdroj: |
ACS Applied Materials & Interfaces; January 2018, Vol. 10 Issue: 1 p1363-1373, 11p |
| Abstrakt: |
Atomically thin transition-metal dichalcogenides (TMDC) have become a new platform for the development of next-generation optoelectronic and light-harvesting devices. Here, we report a Kelvin probe force microscopy (KPFM) investigation carried out on a type-II photovoltaic heterojunction based on WSe2monolayer flakes and a bilayer MoS2film stacked in vertical configuration on a Si/SiO2substrate. Band offset characterized by a significant interfacial dipole is pointed out at the WSe2/MoS2vertical junction. The photocarrier generation process and phototransport are studied by applying a differential technique allowing to map directly two-dimensional images of the surface photovoltage (SPV) over the vertical heterojunctions (vHJ) and in its immediate vicinity. Differential SPV reveals the impact of chemical defects on the photocarrier generation and that negative charges diffuse in the MoS2a few hundreds of nanometers away from the vHJ. The analysis of the SPV data confirms unambiguously that light absorption results in the generation of free charge carriers that do not remain coulomb-bound at the type-II interface. A truly quantitative determination of the electron–hole (e–h) quasi-Fermi levels splitting (i.e., the open-circuit voltage) is achieved by measuring the differential vacuum-level shift over the WSe2flakes and the MoS2layer. The dependence of the energy-level splitting as a function of the optical power reveals that Shockley–Read–Hall processes significantly contribute to the interlayer recombination dynamics. Finally, a newly developed time-resolved mode of the KPFM is applied to map the SPV decay time constants. The time-resolved SPV images reveal the dynamics of delayed recombination processes originating from photocarriers trapping at the SiO2/TMDC interfaces. |
| Databáze: |
Supplemental Index |
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