First principles study of mechanical stability and thermodynamic properties of K₂S under pressure and temperature effect

First principles calculations on structural, elastic and thermodynamic properties of K₂S have been made using the full-potential augmented plane-waves plus local orbitals within density functional theory using generalized gradient approximation for exchange correlation potentials. The ground state lattice parameter, bulk moduli have been obtained. The second-order elastic constants, Young and shear modulus, Poisson ratio, have also been calculated. Calculated structural, elastic and other parameters are in good agreement with available data. The elastic constants and thermodynamic quantities under high pressure and temperature are also calculated and discussed

Functionalized single-walled carbon-nanotube-blended P3HT-based high performance memory behavior thin-film transistor devices

We report on the fabrication and transport properties of single-walled carbon nanotubes (SWCNT) blended with P3HT (poly 3-hexyl thiophene-2, 5-diyl). The composite is used as a hybrid organic active channel transistor. The performances of the fabricated devices were investigated as a function of the SWCNTs' loads in the composite, and their response evaluated under white light illumination. Our results show that for SWCNT loads ≤1.5 wt%, all the devices behave as p-type transistors, exhibiting excellent performance, with an I on /I off ratio of 104 and a maximum on-state current (I on) exceeding 80 μA. Moreover, compared with pristine transistors with a P3HT channel, the Hall mobility of these hybrid TFTs was found to increase by more than one order of magnitude, i.e. increasing from 0.062 to 1.54 cm2 V-1 s-1. Finally, under light illumination, the transfer characteristics (i.e. I DS as a function of V GS) were found to systematically undergo a typical shift together with a fully-reversible memory behavior. A fundamental understanding of this work can assist in providing new routes for the development of reliable efficient hybrid organic-based optoelectronic devices

Influence of single-walled carbon nanotubes induced exciton dissociation improvement on hybrid organic photovoltaic devices

Torch-plasma-grown single-walled carbon nanotubes (SWCNTs) are integrated with regioregular poly(3-hexylthiophene) (P3HT) and a fullerene derivative 1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61 (PCBM) as a hybrid photoactive layer for bulk heterojunction solar cell devices. We demonstrate that molecular information could be accurately obtained by time-of-flight secondary ion mass spectrometry throughout the hybrid organic photoactive solar cell layers when sputtering is performed using a Cs+ 2000 eV ion source. Furthermore, the photovoltaic (PV) performance of the fabricated devices show an increase in the short-circuit current density (Jsc) and the fill factor (FF) as compared to the pristine devices fabricated without SWCNTs. The best results are obtained with 0.5 wt. % SWCNT loads, where an open-circuit voltage (VOC) of 660 mV is achieved, with a Jsc of 9.95 mA cm-2 and a FF of 54%, leading to a power conversion efficiency of 3.54% (measured at standard test conditions, AM1.5 g). At this optimum SWCNT concentration of 0.5 wt. %, and to further understand the charge-transfer mechanisms taking place at the interfaces of P3HT:PCBM:SWCNT, Jsc is measured with respect to the light intensity and shows a linear dependency (in the double logarithmic scale), which implies that losses in the charge carrier are rather governed by monomolecular recombination. Finally, our results show that our hybrid devices benefit from the fullerene electron accepting nature and from the SWCNT fast electron transportation feature that improve substantially the exciton dissociation efficiency. The influence of the SWCNTs on the Fermi level and the work function of the photoactive composite and its impact on the PV performance is also investigated