Amphiphilic fullerene derivative as effective interfacial layer for inverted polymer solar cells

Amphiphilic fullerene derivative with poly(ethylene glycol) chain (C60-PEG) was applied as effective interfacial layer to improve the performance of inverted polymer solar cells. C60-PEG could not only be used as cathode buffer layer alone by replacing ZnO, but also be used as a self-assembled monolayer to modify ZnO. C60-PEG can tune energy level alignment and improve the interfacial compatibility between active layer and ITO or ZnO. Moreover, due to the strong interaction between ZnO nanoparticles and PEG chain, C60-PEG can passivate the surface defects and traps of ZnO, and facilitate the charge selective and dissociation. Consequently, inverted polymer solar cells based on thieno[3,4-b]thiophene/benzodithiophene (PTB7):[6,6]- phenyl C₇₁-butyric acid methyl ester (PC₇₁BM) present a PCE of 6.6% by incorporating C60-PEG into as cathode buffer layer. Moreover, an improved PCE of 7.4% with good long-term stability in air were further achieved by using C60-PEG/ZnO interlayer. In this work, C60-PEG could be prepared by solution process at room temperature without additional annealing, which shows the potential in large-scale printed polymer solar cells.     

Low-voltage solid electrolyte-gated OFETs for gas sensing applications

A polyanionic proton conductor, named poly(4-styrenesulfonic acid) (PSSH), was used to gate an Organic Thin-Film Transistor (OFET) based on p-type poly(2,5-bis(3-tetradecylthiophen-2-yl)thienol [3,2-b]thiophene) (pBTTT-C14) organic semiconductor (OSC). Different device configurations were evaluated and a bottom gate – top contact (BGTC) device was investigated as transducer for gas sensing measurements. The sensors׳ performance in terms of stability, repeatability and reproducibility were evaluated when the device was exposed to different concentrations of 1-butanol. Comparison with a conventionally gated OFET (SiO₂ dielectric instead of PSSH) was also performed.     

Dual layer semiconducting nanocomposite of silicon nanowire and polythiophene for organic-based field effect transistors

We investigate a dual layer active channel of random distributed intrinsic silicon nanowires and solution processing semiconducting polythiophene polymers for organic-based field effect transistors. Primary results show that low density silicon nanowire networks could enhance the effective charge carrier mobility of polythiophene transistors by a factor of six, suggesting that these nanowires act as rapid one-dimensional charge transport bridges in the active channel. Moreover, increasing the nanowire loading in the dual layer nanocomposite could further lessen the transistor hysteresis. The lifetime test of nanowire-polythiophene devices is found to be more sustainable with respect to that of pristine polythiophene in ambient air. These results indicate that semiconducting nanowires should be considered as a viable additive to active channel for next-generation organic field effect transistors.     

有机场效应晶体管输出特性的衰变与恢复

制作了以并五苯作为有源层的有机场效应晶体管（OFETs）。实验观察表明,在原位条件下,器件有很好的输出特性曲线;但在空气中放置3个月后,输出特性曲线明显衰退,并且关态电流增大;为恢复器件性能,在真空条件下,对器件进行加热处理。实验结果表明,经过热处理的晶体管输出特性极大改善。因此,真空热处理可以使衰退器件的输出特性得到...     

Photoprocesses in a semiconducting carbon photocapacitor with a double electrical layer

The possibility is shown of designing a functional hybrid galvanophotocapacitor active system that would be able to use, if necessary, its own chemical energy in darkness instead of only the energy stored during illumination. In experiments, the Bridgman-grown n-type indium monoselenide was used as the photosensitive anode. Electrochemical investigations were carried out in a three-electrode cell with an aprotic solution of electrolyte; 0.4 M lithium-iodide solution in γ-butyrolactone acid and 1M lithium-tetrafluorborate in the same solvent were chosen as the latter.     

Patterning Smectic Liquid Crystals for OFETs at Low Temperature

The preparation of regular microstructures with liquid crystalline materials for organic field effect transistors (OFETs) is an attractive but challenging issue. However, it is usually limited by the difficulty of forming large‐area single crystals aligned in a desirable direction. Herein, several terthiophene (TTP) smectic liquid crystals such as 8‐TTP‐8 and 12‐TTP‐11OH are patterned into highly crystalline microstripes by a sandwich system through a dewetting method. Morphology and orientation of the microstripes strongly depend on preparation temperature. Microstripes prepared below crystalline temperature are uniform, well‐ordered, and show high field effect transistor (FET) mobility. Meanwhile, π–π stacking direction of the TTP backbone is perpendicular to the microstripe and the molecules stack in layer structure, standing up on the SiO₂/Si substrate, which would provide an effective pathway for p‐type charge transport. However, higher preparation temperatures at liquid crystalline or isotropic liquid range induce many defects in the crystal formation process and cause incline of the unit cell, thus leading to a sharp decrease in FET mobility. A possible mechanism of molecular stacking at different temperature range is proposed. This strategy promised to provide a new opportunity for the high cost‐efficiency fabrication of OFETs.     

Electron microscopy analysis of the boundary layer structure of SrTiO3 semiconducting ceramic

In a boundary layer (BL) semiconducting SrTiO3-based ceramic condenser, the BL structure has been investigated using high-resolution field-emission scanning electron microscopy (FE-SEM) and field-emission (scanning) transmission electron microscopy (FE-(S)TEM). In an initial TEM observation, a double layered structure was observed at the grain boundary region. It consisted of a grain boundary (second phase) and a pair of the metal diffusion layers of up to several nanometres in width across the grain boundary where the change of the crystal lattice distance was undetected by the high-resolution TEM image. A facet structure was often observed on the grain boundaries. It was particularly formed on (020) plane of the grain crystal. High resolution SEM showed a jagged striped structure on the surface of the bulk material and on the inside grain as revealed by fracture. Using the similarity in shape and size, it can be identified to correspond to the facet boundary structure. Its formation mechanism can be explained as that during the reoxidization process when the oxide flux of the mixture of Bi2O3, PbO and CuO, painted on the bulk material, surfaces migrates into the ceramic along the grain boundary. The oxide corrodes the grain surfaces including the bulk surfaces. This corrosion particularly occurs on (020) plane of the grain so that the facet structure is produced. In this paper, by using the atomic scale high angle annular dark field STEM, it has been determined that Bi atoms preferentially replace Sr atoms on (020) in the diffusion layers. The atom position displacement was also detected at the grain surfaces and this altered atomic assignment can be determined as an origin of production of Sr2Bi4Ti5O18 at the grain boundary. Also, it was observed that the layer width of the metal diffusion layers was often different between the both grains and changed locally so that the ribbon of the diffusion layers meandered around the straight grain boundary. Its possible mechanism is also proposed.     

Thermal annealing effect on organic semiconducting polymer laser with an external holographic grating feedback layer

Thermal annealing effect on an organic distributed feedback (DFB) laser excited from a semiconducting polymer gain layer, poly(2-methoxy-5-(2’-ethyl-hexyloxy)-p-phenyl-envinylene) (MEH-PPV), is reported. The morphology, absorption and photoluminescence (PL) spectral characteristics of the MEH-PPV film annealed at different temperatures were analyzed. The amplified spontaneous emission (ASE), the optical gain and loss coefficients were also investigated. The organic lasing behaviors including threshold, energy conversion efficiency and polarization state in a DFB laser device were studied. The results show that the optical properties of the organic semiconducting laser can be enhanced by thermal annealing effect. The single mode laser emission at 622.4 nm with lower lasing threshold 0.2 μJ/pulse and higher energy conversion efficiency 6.71% was achieved with thermal annealing at 120 °C. The thermal annealing treatment decreases laser threshold and increases laser energy conversion efficiency dramatically, which shows the potential in ultra-low cost organic semiconducting polymer DFB lasers.     

Poly(arylenethynyl-thienoacenes) as candidates for organic semiconducting materials. A DFT insight

The conducting properties for holes and electrons of a set of 16 poly(arylenethynyl-thienoacene) derivatives as candidates for organic semiconductors have been theoretically studied at density functional theory (DFT) level. Some of the selected compounds show adequate values of charge carrier mobilities and injection parameters to be considered either p- or n-type organic semiconductors, although they all show high LUMO energy levels as compared to the Fermi level of Au electrode, decreasing their feasibility as ambipolar semiconductors. Derivatization with electron withdrawing moieties (F and CN) permits to suggest some of the studied compounds to display balanced both ease charge injection and high charge mobilities for holes and electrons, which could allow high performances as ambipolar semiconductors.     

Highly enhanced electron injection in organic light-emitting diodes with an n-type semiconducting MnO2 layer

Highly enhanced electron injection is demonstrated with a thin manganese dioxide (MnO₂) electron injection layer (EIL) in Alq₃-based organic light-emitting diodes. Insertion of the MnO₂ EIL between the Al cathode and Alq₃ results in highly improved device characteristics. In situ photoelectron spectroscopy shows remarkable reduction of the electron injection barrier without significant chemical reactions between Alq₃ and MnO₂, which could induce Alq₃ destruction. The reduction of the electron injection barrier is due to the n-type doping effect, and the lack of strong interfacial reaction is advantageous with regards to more efficient electron injection than a conventional LiF EIL. These properties render the MnO₂, a potential EIL.     

Electrical contacts for II-VI semiconducting devices

High resistivity II-VI semiconductors in general and CdTe and its associated materials like CdZnTe and CdMnTe in particular are suffering from ohmic contacting problem due to their high electron affinity and consequently large work function. Ni, Au, Pt and Pd have large work function and have possibility to match with the above materials. However, except Ni other materials have problems in large-scale commercial applications. In order to overcome the ohmic contacting problem to these semiconductors the following studies has been conducted in the text of the present paper. These are: (i) Work function engineering to modulate the work function through combination materials like, Cu, Au, Mo, W and Co. (ii) Introduction of a charge diluting intermediate semiconducting layer media in between the metal and CdTe to neutralize the bound polarized charges. These two aspects were applied in case of thin film CdTe-CdS solar cells to evaluate their contacting performances and their influences in solar cell parameters. Both cell performances and the contact characteristics of these contacting technologies were studied at depth and indicated their applicability in semiconducting devices.     

VMTP as the transport layer for high-performance distributedsystems

The authors identify and discuss three major categories of deficiencies in current transport protocols: performance, naming, and functionality. They describe the design of the Versatile Message Transaction Protocol (VMTP) and some performance measurements of the protocol used in the V-Distributed System. They show that VMTP addresses all of the above issues within a single protocol without significant compromise     

Inkjet printable and low annealing temperature gate-dielectric based on polymethylsilsesquioxane for flexible n-channel OFETs

We report on inkjet printable gate-dielectric based on a spin-on-glass (SOG) material for applications in n-type organic field-effect transistors (OFETs). The SOG material is polymethylsilsesquioxane in alcohol mixture. After annealed at 135 °C in air, the SOG films are well crosslinked and have a good resistance against alcohol, which allows for the inkjet printing of Ag gate electrodes on top of the SOG dielectric. The crosslinked SOG films are very dense, and can withstand high electric field. This is very beneficial to the operation of transistors. In addition, the SOG films have very low hydroxyl content after annealing. This property is very important for n-type transistors. After ink formulation, this SOG dielectric has an excellent inkjet-ability with good uniformity and reproducibility. By using Polyera's P(NDI2OD-T2) as the semiconductor and SOG as the dielectric, bottom-contact top-gated n-type transistors were successfully fabricated on PET substrates with electron mobility above 0.1 cm²/V and high on/off ratio well above 10⁵. These remarkable results demonstrate that this newly formulated SOG dielectric is a promising candidate for the future development of flexible electronic devices.     

Circuit modelling for electromagnetic compatibility

Sophisticated software is widely available in the form of mathematical and circuit analysis packages. This computing power can be harnessed to assess the electromagnetic coupling between signals in a system and currents in the structure. To achieve this objective, it is necessary to have reliable circuit models of the coupling parameters. A method of formulating such models is described, illustrating key relationships between circuit theory and electromagnetic theory. It is shown how general-purpose testing can be used to refine any model, and how the results of formal testing can be predicted     

Atomic layer deposited Al2O3 as a capping layer for polymer based transistors

The strong sensitivity of organic/polymeric semiconductors to the exposure to O₂ and H₂O atmospheres makes the use of capping layers mandatory for the realization of stable devices based on such materials. In this paper we explore the realization of inorganic capping layers by atomic layer deposition (ALD) that provides smooth and pinhole-free films with a great potential as passivation layer for organic based devices. We show that the deposition of Al₂O₃ on transistors based on poly-3 hexyltiophene (P3HT) allows to obtain air stable devices. Whereas the growth of Al₂O₃ directly on the P3HT layer leads to a rough interface and significant intermixing between the oxide and the polymer, which results in a deterioration of transistor performances, an interlayer of a poly-alcohol such as poly-vinylphenol interposed between the Al₂O₃ and the P3HT gives a well defined Al₂O₃/polymer interface without degradation of the hole mobility. Transistors capped with Al₂O₃/PVP are very stable in air, with no appreciable differences in the electrical characteristics when measured in vacuum or in air. In addition no significant degradation of the transistors electrical properties was detected even after one month of air exposure.     

Photosensitivity of top gate C60 based OFETs: Potential applications for high efficiency organic photodetector

The comparison of light-induced effects in bottom-gate and top-gate organic field effect transistors (OFETs) provide a clear indication, that the nature of interface between the active layer and the gate dielectric plays a major role in the observed light-induced threshold voltage shift. The nature of interface was also analyzed by electron spin resonance (ESR) experiments, which provides a direct evidence for the creation of free radical species when parylene is deposited on the top of the C₆₀ semiconductor layer. The rate of change of light-induced threshold voltage shift strongly depends on the wavelength and intensity of the incident light, and transverse electric field at the interface. The observed effects provide a strong base for the realization of high efficiency organic photodetectors and optical memory devices. The responsivity of organic photodetector was measured up to 1047 A/W.     

Laser scanning for electronic printing

The use of laser scanning techniques for acquisition and printing of images is reviewed with primary emphasis on the printing application. Following an introduction to the basic configuration of laser scanners and to the terminology of this field, some of the principal characteristics of these scanners are summarized. A short overview is given of the key components of scanners, i.e., lasers, modulators, and light deflectors. The integration of these and other components into complete scanning systems is then described, including discussion of optical design issues and several examples of practical optical system design for polygon scanners. Holographic scanners and some of their design considerations are discussed. The electronic and mechanical techniques required for satisfactory scanner design and construction are described. Finally, the embodiment of various design approaches into practical scanners is illustrated by a survey of some existing printer products.     

ZnO nanoparticles as a luminescent down-shifting layer for photosensitive devices

The optical properties of ZnO nanoparticles(NPs) fabricated by three different methods were studied by the UV-excited continuous wave photoluminescence in order to estimate their down-shifting(DS) efficiency. Such a luminescent layer modifies the incident solar radiation via emitting wavelengths better matching the spectral response of the underlying photosensitive device(photodiode),thereby increasing its efficiency.Some of the studied ZnO NPs were subsequently deposited on the front side of commercial silicon photodiodes and the external quantum efficiency(EQE) characteristics of the final devices were measured.Through comparison of the photodiode’s EQE characteristics before and after the deposition of the ZnO NPs layer,it was concluded that for the photodiode with a low UV sensitivity(about 8%),the ZnO luminescent layer produces a down-shifting effect and the EQE in the UV and blue range improves by 16.6%,while for the photodiodes with a higher initial UV sensitivity(about 50%),the EQE in this range decreases with the ZnO layer thickness,due to the effects competing with DS,like the diminution of the ZnO layer transmittance and an increasing diffusion.     

Trisneopentylgallium as a precursor for atomic layer epitaxy of GaAs

We report the use of a new precursor, trisneopentylgallium (NPG) for the growth of GaAs by atomic layer epitaxy (ALE). In contrast to most other alkyl gallium precursors such as triethylgallium, which decompose via a β-hydride elimination mechanism, this compound undergoes homolysis similar to that of trimethylgallium (TMGa), the normal choice as an ALE precursor. Clear self-limiting growth behavior similar to that of TMGa was observed over a reasonably wide range of growth conditions (430–500°C). Carbon incorporation was not significantly reduced compared with TMGa suggesting that the adsorbed neopentyl radicals undergo decomposition to result in a methyl terminated surface identical to that obtained for growth with TMGa.     

Parameter compatibility relations for accelerated testing

It is pointed out that the use of acceleration studies implies that stress does not change the mechanisms of failure but only contracts the time to reach failure level. This implication is translated into a requirement that the parameter set for the failure distribution does not change, but values of the parameters may. The generality of the relationship between parameter values at various stress levels and the time transformation that connects the respective distributions is emphasized. These are termed compatibility relations. An example of compatibility relations for acceleration studies described by a Weibull distribution is given in detail. The compatibility relations between the coefficients in the time transformation in acceleration studies based on exponential, gamma, log-normal, and Weibull distributions and respective parameter values are discussed generally. Compatibility relations can be used to improve estimation procedures, check the consistency of parameter estimation during analysis of acceleration test data, and check the validity of the use of acceleration studies in the first place