Transition metal oxides on organic semiconductors

Transition metal oxides (TMOs) on organic semiconductors (OSs) structure has been widely used in inverted organic optoelectronic devices, including inverted organic light-emitting diodes (OLEDs) and inverted organic solar cells (OSCs), which can improve the stability of such devices as a result of improved protection of air sensitive cathode. However, most of these reports are focused on the anode modification effect of TMO and the nature of TMO-on-OS is not fully understood. Here we show that the OS on TMO forms a two-layer structure, where the interface mixing is minimized, while for TMO-on-OS, due to the obvious diffusion of TMO into the OS, a doping-layer structure is formed. This is evidenced by a series of optical and electrical studies. By studying the TMO diffusion depth in different OS, we found that this process is governed by the thermal property of the OS. The TMO tends to diffuse deeper into the OS with a lower evaporation temperature. It is shown that the TMO can diffuse more than 20 nm into the OS, depending on the thermal property of the OS. We also show that the TMO-on-OS structure can replace the commonly used OS with TMO doping structure, which is a big step toward in simplifying the fabrication process of the organic optoelectronic devices.     

Multifunctional π-conjugated poly (3-methylthiophene) nanotubes for optoelectronic and field emissive devices

Multifunctional properties of nanomaterials becomes a hot topic in nano research for the development of multifunctional devices, because modern devices need multifunctional platform for the high efficient plural performance on a single device. Here, we introduce a multifunctional π-conjugated poly (3-methylthiophene) (P3MT) nanotube (NT), showing controllable optical and electrical properties through the control of doping level. P3MT NTs were electrochemically synthesized in the low temperature (−40 °C) on the nanoporous template. The change of doping level by post cyclic voltammetry (CV) treatment on the P3MT lead the variance of polaron/bipolaron band, resulting into the drastic change of ultraviolet-visible absorption and photoluminescence properties. While P3MT NTs before CV treatment show an ohmic behavior in the current-voltage characteristics, those after CV treatment show high photocurrent. From the field emission experiment, the P3MT NTs before CV treatment have a relatively low turn-on electric field and stable electron emission property compared to the P3MT NTs after CV treatment. This shows that the π-conjugated polymers should be shed new light on their multifunctionality for the potential application to the multifunctional platform of opto-electronic nanodevices.     

SQM-OTFT: A compact model of organic thin-film transistors based on the symmetric quadrature of the accumulation charge considering both deep and tail states

A physically-based compact model of organic thin-film transistors suitable for CAD simulators is proposed. It is worked out by means of a newly developed and particularly simple form of the charge-sheet model: the symmetric quadrature of the accumulation charge. The model is based on the variable-range hopping and accounts for both deep and tail states. It is simple, symmetric, accurately accounts for the below-threshold, linear, and saturation regimes via a unique formulation. The symmetric quadrature is accurate within 5% in all regions of operation and the resulting current model is suitable both for p- and n-type transistors. The model leads to a significant simplification of the drain current and of the quasi-static expressions of the terminal charges based on the Ward–Dutton partition. Finally, the symmetric quadrature leads to an explicit and analytically tractable solution for the surface potential as a function of position in the device channel that can be extremely useful to implement advanced physical effects.     

Genetic and environmental influences on problematic Internet use: A twin study

Despite many studies on the prevalence and correlates of problematic Internet use (PIU), we know little about its etiological components. Our main aim is to find out to what extent PIU is influenced by genetic and environmental factors using the classic twin design. A total of 237 Turkish twin-pairs aged 10–25 participated in the study. PIU was measured using the ‘Problematic Internet Use Scale’ (PIUS) developed by Ceyhan, Ceyhan and Gürcan. For male twin-pairs, the monozygotic (MZ) twin correlations were larger than the dizygotic (DZ) twin correlations, indicating that genetic factors influenced scores on the PIUS. However, for female twin-pairs, the MZ correlations were smaller than the DZ correlations for the PIUS, showing that genetic factors did not play a role in female twin-pairs. The influence of both genetic and environmental factors was explored with model-fitting analysis. Results showed that both for the “social comfort/benefit” and “negative consequences associated with the Internet use” sub-dimensions, the best-fitting models were the ADE models whereas both for the “excessive use” sub-dimension and “PIUS-Total”, the best-fittings models were the ACE models. The key result of this study is that the genetic and non-shared environmental effects are equally influential on the overall PIU in male twin-pairs.     

Structural,electronic, and magnetic properties of zigzag-edged BN nanoribbons with 558-type line defects

The 558-type line defect is introduced into zigzag-edged BN nanoribbons (ZBNNRs), similar to that be found in graphene, and the structural, electronic, and magnetic properties for such defective ZBNNRs are investigated systematically. It shows that they are highly stable. In the nonmagnetic state, the metallic property of ZBNNRs remains unchanged regardless of the defect positions, but different defect positions give rise to different influences on the total DOS and PDOS at the Fermi level. Interestingly, in the magnetic state, the thermal stability of magnetism is enhanced greatly when the line defect appears at most positions, even comparable with room temperature. When the line defect position shifts from the B-edge to the N-edge, the transition from the half-metal to the magnetic semiconductor or spin unpolarized semiconductor is induced. And also, the response of defect ribbons to an in-plane transverse electric field is essentially different from defect-free ribbons, and the half-metallic feature can be enhanced by an electric field for the line defect introduced into certain positions in a ribbon.     

Graphene nanosheets as counter electrode with phenoxazine dye for efficient dye sensitized solar cell

Efficient dye sensitized solar cells (DSSCs) are developed using phenoxazine (POZ) based organic dye (WS5) and graphene nanosheets (GNs) counter electrode (CE). Being organic, both these materials are used together to explore compatibility of organic materials in current DSSCs. Organic dye with POZ moiety is synthesized and graphene oxide nanosheets (GONs) are spin coated on FTO glass and thermally reduced afterwards. To increase the performance of WS5 through decreased dye aggregation, deoxycholic acid (DCA) is added to it. The results of adding DCA are observed and compared using UV–Vis spectroscopy, external quantum efficiency (EQE), electrochemical impedance spectroscopy (EIS) and photovoltaic conversion efficiency (PCE). Prepared organic dye based DSSC cell results in a high PCE of 6.61%. The optimized WS5 dye and GNs CE, shows PCE of 5.77% and the GNs CE compared to Pt CE results in almost identical charge transfer resistance value at the CE/electrolyte interface. Low cost of this designed organic dye and GNs and the PCE results indicate that this combination may result in the reduction of cost of current DSSCs and the realization that expensive and rare inorganic materials can be replaced with organic ones in future.     

High-efficiency orange and white phosphorescent organic light-emitting diodes based on homojunction structure

We demonstrate high-efficiency orange and white phosphorescent organic light-emitting diodes based on homojunction structure. Excellent performance is realized by using step-graded p- and n-type doping structure in orange homojunction device. The resulting orange homojunction device exhibits a maximum current efficiency of 30.0 cd/A and low efficiency roll-off. The improvements are mainly attributed to the utilization of step-graded doped profile, which facilitates balanced charge carrier injection and transport. Moreover, one optimized white homojunction device based on two complementary colors shows a maximum efficiency of 15.4 cd/A, and superior color-stability in a wide range of luminance.     

Proposal and investigation of photonic data selector based on cross-phase modulation in a highly nonlinear fiber

It is proposed and demonstrated a design of 2-to-1 photonic data selector based on the cross-phase modulation in a highly nonlinear fiber. By using bidirectional configuration, this scheme has potentially advantages of cost effective and simple structure. The correct output logic function is obtained at 40 Gbit/s without using any additional input light beams. In addition, the output signals have a single spectrum component by reasonable selecting input signals wavelength, which is important for transmission and scalability. The dependences of performances on signal wavelength, pump power, the temporal relative position of pulses, as well as the OSNR and chirp of input signals are calculated and discussed respectively, showing impressive operation performance. This scheme could be a promising candidate for future ultrafast all-optical signal processing applications.     

Power harmonics analysis of programmable AC power source via variation semi-sinusoidal window

Harmonic contents are employed for indicating the quality of the programmable AC power source (PACPS). However, spectrum leakage usually occurs. This paper employs a variation semi-sinusoidal window (VSSW) for performing the power harmonic analysis. Since the rolloff of the sidelobes of the VSSW is fast, experimental results show that the VSSW outperforms existing windows.