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Self‐assembled monolayers (SAMs) are widely employed in organic field‐effect transistors to modify the surface energy, surface roughness, film growth kinetics, and electrical surface potential of the gate oxide to control the device's operating voltage. In this study, amino‐functionalized SAM molecules are compared to pure alkylsilane SAMS in terms of their impact on the electrical properties of organic field‐effect transistors, using the n‐type polycrystalline small molecule semiconductor material N,N′‐dioctyl‐3,4,9,10‐perylenedicarboximide (PTCDI‐C8). In order to understand the electronic impact of the amino groups, the effect of both the number of amino‐containing functional groups and the SAM molecular length are systematically studied. Though amino‐functionalized SAM materials have been studied previously, this study is, for the first time, able to shed light on the nature of the doping effect that occurs when the gate oxide is treated with polar aminosilane materials. By a comprehensive theoretical study of the interface on the molecular level, it is shown that the observed shift in the threshold voltage is caused by free charges, which are attracted to the PTCDI‐C8 and are stabilized there by protonated aminosilanes. This attraction and the voltage shift can be systematically tuned by varying the length of the neutral terminal chain of the aminosilane. [ABSTRACT FROM AUTHOR]

Derivatives of the hexacyano‐[3]‐radialene anion radical (CN6‐CP•−) emerge as a promising new family of p‐dopants having a doping strength comparable to that of archetypical dopant 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyano‐quinodimethane (F4TCNQ). Here, mixed solution (MxS) and sequential processing (SqP) doping methods are compared by using a model semiconductor poly(3‐hexylthiophene) (P3HT) and the dopant CN6‐CP•−NBu4+ (NBu4+ = tetrabutylammonium). MxS films show a moderate yet thickness‐independent conductivity of ≈0.1 S cm−1. For the SqP case, the highest conductivity value of ≈6 S cm−1 is achieved for the thinnest (1.5–3 nm) films whereas conductivity drops two orders of magnitudes for 100 times thicker films. These results are explained in terms of an interfacial doping mechanism realized in the SqP films, where only layers close to the P3HT/dopant interface are doped efficiently, whereas internal P3HT layers remain essentially undoped. This structure is in agreement with transmission electron microscopy, atomic force microscopy, and Kelvin probe force microscopy results. The temperature‐dependent conductivity measurements reveal a lower activation energy for charge carriers in SqP samples than in MxS films (79 meV vs 110 meV), which could be a reason for their superior conductivity. [ABSTRACT FROM AUTHOR]

Dopants, i.e., electronically active impurities, are added to organic semiconductor materials to control the material's Fermi level and conductivity, to improve injection at the device contacts, or to fill trap states in the active device layers and interfaces. In contrast to bulk doping as achieved by blending or co-deposition of dopant and semiconductor, surface doping has a lower propensity to introduce additional traps or scattering centers or to even alter the layer morphology relative to the undoped active material layers. In this study, the electrical effects of a very simple, post-device-fabrication surface doping process involving various amine group-containing alkoxysilanes on the performance of organic field-effect transistors (OFETs) made from the well-known n-type materials PTCDI-C8 and N2200 are researched. It is demonstrated that OFETs doped in such a way generally show enhanced characteristics (up to 10 times mobility increase and a significant reduction in threshold voltage) without any adverse effects on the devices' on/off ratio. It is also shown that the efficiency of the doping process is linked to the number of amine groups. [ABSTRACT FROM AUTHOR]

Abstract: Organic field‐effect transistors based on aligned small molecule semiconductors have shown high charge carrier mobilities in excess of 10 cm2 V−1 s−1. This makes them a viable alternative to amorphous inorganic semiconductors especially if a high reproducibility can be achieved. Here, the optimization of high mobility organic field‐effect transistors based on the organic semiconductor 2,7‐dioctyl[1]benzothieno[3,2‐b] benzothiophene (C8‐BTBT) via the addition of a polymer additive to the printing solution is reported. Specifically, films and devices are compared based on solutions of the neat semiconductor and the blend with polystyrene and shear‐coated devices with excellent device characteristics and gate‐voltage‐independent mobility values reaching 12 cm2 V−1 s−1 are shown, which are the highest reported values for C8‐BTBT‐based films prepared by a scalable, solution‐based process. [ABSTRACT FROM AUTHOR]

Solution-processable non-polymeric organic semiconductors are attractive for opto-electronic applications due to their relatively simple synthetic reproducibility and characterization, and enhanced capability for fine-tuning of their properties. We report the synthesis, charge transport, photophysics, and photovoltaic properties of three non-polymeric materials based upon bisarylthiophenyl diketopyrrolopyrrole [DPP(ThAr) 2 ]. The DPP(ThAr) 2 molecules are comprised of solubilizing alkyl groups, 2-ethylhexyl (for 1a ) and 2-octyldodecyl (for 1b and 2 ), which are capped with "electron accepting" moieties - fluorenone ( 1 ) or benzothiadiazole ( 2 ). While the materials could be prepared under standard Suzuki-Miyaura cross-coupling conditions, a simple direct arylation afforded 2 and 1b in good yields. We found 1a with a short alkyl chain lacked sufficient solubility for solution processing but 1b and 2 are solution processable and form good quality films. All three materials exhibited ambipolar charge transport in field effect transistors, with 1b showing balanced charge mobilities of about 10 −3 cm 2 V −1 s −1 . Bulk heterojunction solar cells of 1b or 2 with PC71BM were found to have high open-circuit voltages (up to 0.9 V) with power conversion efficiencies of up to 4.5% and 2.6%, respectively. [ABSTRACT FROM AUTHOR]

We present ITO-free rigid and flexible monolithic organic solar cells with an active area of 25 cm 2 . The devices employ a transparent insulator/metal/insulator anode consisting of a molybdenum oxide/silver/zinc sulfide stack that had a peak transmittance of 80% and a sheet resistance of 3.6 Ω/□. Neutron reflectometry showed that zinc sulfide formed a more stable capping layer at the air interface than molybdenum oxide. It was found that blade coating could be used to form good quality large area films on both rigid (glass) and flexible [poly(ethylene terephthalate)] substrates with much reduced material consumption. Cells with an active layer comprised of a blend of poly[ N -9″-heptadecanyl-2,7-carbazole- alt -5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 70 BM) gave a power conversion efficiency of 2.7%, which was 40% higher than a standard ITO-based device. No loss in efficiency was observed when a flexible substrate was used. [ABSTRACT FROM AUTHOR]

With the prospect of realizing innovative technologies by large‐area fabrication at low cost and high throughput, printing and coating technologies are being intensively researched for the deposition of functional films. One promising coating technology is solution shearing, which has been studied as a deposition technique for organic semiconductors but not to a greater extent for dielectric layers. Therefore, the deposition by solution shearing of high‐quality poly(4‐vinylphenol) dielectrics is investigated, and the utility of these films as ultra‐smooth dielectric substrates for transistors is demonstrated. By comparing these films to those prepared by spin‐coating, it is possible to highlight the advantages of the technique. Specifically, thinner films with thicknesses as low as 11.4 nm but still low leakage and almost identical surface properties can be achieved. Thus, dielectric films with a very high capacitance of 280 nF cm‐2 are realized in a single coating step. Probing these films within organic transistors shows that they can facilitate operation at voltages as low as ‐1 V. Finally, it is shown how the use of a polymer‐small‐molecule–semiconductor blend can pave the way toward high‐performance, ultra‐low‐voltage devices from solution. [ABSTRACT FROM AUTHOR]

Here, we show the fabrication of sub-micrometer channel devices that are patterned by a simple inclined thermal evaporation approach. This structuring methodology with the capability to produce electrodes with distances even below 100 nm is compatible with solution-based fabrication methods commonly applied to deposit high-mobility organic semiconductor films or even high-capacitance polymer gate dielectrics. As the contacts are directly defined through thermal evaporation without the need for any expensive masks or lithography techniques, it offers the possibility of simple, lab-scale assessment of promising material combinations in the development of high-performance organic transistors through direct access to sub-micrometer channel device characteristics. Here, we focus on the structuring method, show example devices with sub-micrometer channel lengths, and discuss the potential applications of this methodology as a lab-scale test vehicle for OFET development. [Display omitted] • Lithography-free approach for defining sub-micrometer transistor channels. • Short-channel fabrication on top of organic semiconductor. • Compatible with soluble organic semiconductors. [ABSTRACT FROM AUTHOR]