Organic semiconductors have been the subject of active research for over a decade now, with applications emerging in light-emitting displays and printable electronic circuits. One characteristic feature of these materials is the strong trapping of electrons but not holes: organic field-effect transistors (FETs) typically show p-type, but not n-type, conduction even with the appropriate low-work-function electrodes, except for a few special high-electron-affinity or low-bandgap organic semiconductors. Here we demonstrate that the use of an appropriate hydroxyl-free gate dielectric--such as a divinyltetramethylsiloxane-bis(benzocyclobutene) derivative (BCB; ref. 6)--can yield n-channel FET conduction in most conjugated polymers. The FET electron mobilities thus obtained reveal that electrons are considerably more mobile in these materials than previously thought. Electron mobilities of the order of 10(-3) to 10(-2) cm(2) V(-1) s(-1) have been measured in a number of polyfluorene copolymers and in a dialkyl-substituted poly(p-phenylenevinylene), all in the unaligned state. We further show that the reason why n-type behaviour has previously been so elusive is the trapping of electrons at the semiconductor-dielectric interface by hydroxyl groups, present in the form of silanols in the case of the commonly used SiO2 dielectric. These findings should therefore open up new opportunities for organic complementary metal-oxide semiconductor (CMOS) circuits, in which both p-type and n-type behaviours are harnessed.

In this work, we reported high performance OLED devices with transparent and conductive carbon nanotube anodes after modification. The modifications include IMRE proprietary PEDOT:PSS composite top coating (PS(C)), concentrated HNO(3) acid soaking, and polymer encapsulation. For PS(C)-modified nanotube thin film anode, we achieved maximum luminescence of approximately 9000 cd/m(2), close to ITO-based OLED device performance, and high efficiency of approximately 10 cd/A, similar with ITO-based OLED device. The performance is approximately 30 to 450 times better than that achieved for OLED devices using CNT anodes by others. In addition, we also investigate the mechanical property, work function, sheet resistance, and surface morphology of modified carbon nanotube thin-film anodes.

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Fourier-transform infrared spectroscopy of two prototypical high-mobility polymer organic semiconductors (OSCs), regioregular poly(3-hexylthiophene) (rr-P3HT) and poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno(3,2-b)thiophene] (PBTTT), reveals photoinduced doping that involves both oxygen and water dissolved in the polymer matrix when exposed to light. The equilibrium concentration of water at room temperature and 60% relative humidity in these films is $2 Â 10 19 cm À3, and exists primarily as monomers, with a small population of dimers and trimers. Photo-excitation in room light ultimately generates a polaron density of the order of a few 10 17 cm À3, which is sufficient to degrade the saturation and 'on-off' characteristics of organic field-effect transistors, and the dark current of organic photovoltaics. The dopant anion has been identified primarily to be hydroxide ion species. This process occurs to a smaller extent in wet nitrogen, but even less in dry oxygen, which points to a key role of the dissolved water. The relative stability of PBTTT over rr-P3HT is found to be largely kinetic in origin, attributed to its higher crystallinity (X-ray diffraction crystallinity 27% vs 21% in rr-P3HT), and shorter pÁÁÁp stacking distance (3.64 Å vs 3.78 Å in rr-P3HT), which gives better moisture exclusion from its thiophene backbone.Understanding the degradation mechanisms of polymer organic semiconductor (OSC) devices is an essential step to develop more robust OSC systems and their devices, whether in light-emitting diodes (LEDs), field-effect transistors (FETs), or photovoltaics (PVs). Despite decades of research, detailed spectroscopic studies have seldom been reported, [1,2] primarily because of the considerable challenges to identify chemical transformations that occur on sub-1-mol % of repeat units in the thin films. Yet changes at these levels can be electronically significant. The typical carrier density for LED operation [3] is $1 Â 10 18 cm À3 , which is approximately 0.05 mol % of repeat units, assuming a unit molecular weight of 300 g mol À1 and density of 1.1 g cm À3. For organic FETs, doping at this level can open a parallel source-drain conduction path in the bulk that degrades the shut 'off' and saturation characteristics. [4,5] A simple performance figure-of-merit is the 'on-off' ratio, which for long-channel FETs with a small drain voltage V d and an off-state defined at a gate voltage (V g ) of 0 V is given by i on / i off ¼ mC ox (V g À V th )/(sd), where m is the carrier mobility, C ox is the gate-dielectric capacitance, (V g À V th ) is the effective gate voltage, s is the shunt conductance, and d is the film thickness. For m $ 0.1 cm 2 V À1 s À1 , d $ 30 nm, and typical values for the other parameters, we require s < 10 À8 S cm À1 to give an i on /i off ratio > 10 6

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