In this work, we investigate the transverse transport properties of few-layers MoS2 using a Conductive Atomic Force Microscopy based technique. We find that the system changes between a low-force regime, characterized by a nearly-ideal contact between the MoS2 flake and the substrate, and a high-force regime, for which this contact starts to become highly non-ideal. We propose a 3-diode model that effectively describes the current-voltage characteristics of few-layers MoS2. From this model, we estimate how fast the energy gaps of two-dimensional MoS2 materials change as a function of the applied force. From our analysis, we estimate that MoS2-Au Schottky barrier heights change at the rate of 0.21, 0.23, and 0.78 meV nN−1 for the few-layers, three-layers, and two-layers MoS2, respectively. Our work opens up new possibilities of investigating and controlling the electronic properties of 2D semiconducting materials.
Cobalt ferrite (CoFe 2 O 4) nanoparticles (NPs), with an average diameter of about 4-10 nm, were produced by the proteic sol-gel method and successfully doped into the active layer of poly(3-hexylthiophene-2,5diyl) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) organic solar cells. Pristine and CoFe 2 O 4 NPs-doped blends of P3HT:PCBM were dispersed in a mixture of o-xylene:tetralin (1 mg/mL) based non-halogenated solvents and deposited via a semi-industrial blade coating process on flexible substrates to fabricate large area (0.55 cm 2), flexible organic solar cells with inverted configuration. The main focus of this study aims to assess the influence of NPs on the efficiency, stability and lifetime of the produced devices. From the photovoltaic parameters it was observed that the optimization of the bulk-heterojunction through the incorporation of CoFe 2 O 4 NPs resulted in increased short-circuit current density. As a result, the power conversion efficiency of doped devices increased by 10 % when compared with the undoped reference devices. Tests of lifetime and stability were performed using International Summit on OPV Stability (ISOS) protocols ISOS-D-3, ISOS-O-1 and ISOS-L-1. For the duration of the tests (1200 h), the results showed that doped cells presented performances at least comparable with those of reference cells.
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