A series of N-heteroheptacenes was synthesized from ortho-thiophene-substituted aryl azides using a Rh-2(II)-catalyzed C-H bond amination reaction to construct the thienoindole moieties. This reaction tolerated the presence of electron-donating or withdrawing groups on the aryl azide without adversely affecting the yield of the amination reaction. The central thiophene ring was created from two thienoindole pieces through a Pd-catalyzed Stille reaction to install the thioether followed by a Cu-mediated Ullman reaction to trigger the cyclization. The photophysical and electrochemical properties of the resulting focused library of N-heteroheptacenes revealed that the electronic nature is controlled by the arene substituent while single crystals grown reveal that the packing motif is influenced by the N-substituent. Solution-processed thin-film OFET devices were fabricated with the N-heteroheptacenes, and one exhibited a hole-mobility of 0.02cm(2)V(-1)s(-1).

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Benzo[d][2,1,3]thiadiazole (BT) is a markedly electron-deficient heterocycle widely employed in the realization of organic semiconductors for applications spanning transistors, solar cells, photodetectors, and thermoelectrics. In this contribution, we implement the corresponding isomer, benzo[d][1,2,3]thiadiazole (isoBT), along with new 6-fluoro-isoBT and 5,6-difluoro-isoBT units as synthons for constructing alternating copolymers with tetrathiophene (P1–P3). New isoBT-based small molecules as well as the corresponding BT-quaterthiophene based polymers (P4–P6) are synthesized and characterized to probe architectural, electronic structural, and device performance differences between the two families. The results demonstrate that isoBT complements BT in enabling high-performance optoelectronic semiconductors with P3 exhibiting hole mobilities surpassing 0.7 cm2/(V s) in field-effect transistors and power conversion efficiencies of 9% in bulk-heterojunction solar cells.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Semiconducting bispyrrolothiophenes for thin film organic field effect transistors were constructed from vinyl azides using transition-metal-catalyzed CH bond functionalization. Pictured is an AFM image of one of the polycrystalline bispyrrolothiophenes that exhibited good field effect transistor performance despite its amorphous nature. For more information see the Full Paper by A. Facchetti, T. G. Driver et al. on page 5938 ff.

The frequency response of unipolar organic Schottky diodes used in a rectifying circuit, such as an RFID tag, has been investigated in detail. The time dependent response of rectifying circuits has been simulated solving both the Drift Diffusion and Poisson equations to model the hole transport within the diode, coupled with time dependent circuit equations. Several approximations have also been discussed. It turns out that the cut off frequency of the rectifying circuit is indeed limited by the carrier time-of-flight and not by the diode equivalent capacitance. Simulations have also been confirmed by comparison with experiments, involving diodes with different mobilities and thicknesses. This work confirms that the 13.56MHz frequency can be reached using polymer semiconductors, as already experimentally demonstrated in the literature, by an adequate control of the active layer thickness. (C) 2014 AIP Publishing LLC.

A series of new highly soluble bispyrrolothiophenes were synthesized from vinyl azides by using transition-metal-catalyzed C-H-bond functionalization. In addition to modifying the substituents present on the end-pyrrolothiophene moieties, the arene linker in between the two units was also varied. The solution-state properties and field-effect-transistor (FET) electrical behavior of these bispyrrolothiophenes was compared. Our investigations identified that the optical properties and oxidation potential of our compounds were dominated by the pyrrolothiophene unit with a λmax  value of approximately 400 nm and oxidation at approximately 1 V. FET devices constructed with thin films of these bispyrrolothiophenes were also fabricated by means of thin-film solution processing. One of these compounds, a bispyrrolothiophene linked with benzothiodiazole, exhibits a mobility of approximately 0.3 cm(2)  V(-1)  s(-1) and the Ion/Ioff value is greater than 10(6).

The electron acceptor building block for pi-conjugated copolymers, 3,6-dithiophen-2-yl-diketopyrrolo[3,2-b]pyrrole (isoDPPT), was synthesized following two routes. The comparison between isoDPPT and widely investigated 3,6-dithiophen-2-yl-diketopyrrolo[3,4-c]pyrrole (DPPT) in terms of molecular orbital computations, single crystal X-ray diffraction, optical absorption and cyclic voltammogram was utilized to elucidate structural and electronic structure differences between the two cores. Both units are found to be planar in the solid state, exhibit similar LUMO energy, however, isoDPPT exhibits a much deeper HOMO energy. Six isoDPPT-based polymers with optical bandgaps spanning from 1.44 to 1.76 eV were synthesized by copolymerizing isoDPPT with the following building blocks: 2,2'-bithiophene (for P1), 4,4'-bis(2-ethylhexyl)-dithieno[3,2-b:2',3'-d]silole (for P2), 3,3'''-didodecylquaterthiophene (for P3), 4,8-didodecylbenzo[1,2-b:4,5-b']dithiophene (for P4), 4,8-didodecyloxybenzo[1,2-b:4,5-b']dithiophene (for PS) and 3,3'-bis(dodecyloxy)-2,2'-bithiophene (for P6). Field-effect transistors and bulk heterojunction solar cells based on isoDPPT copolymers were fabricated and the response compared vis-a-vis to those of some DPPT-based polymers. Hole mobility (mu(h)) of 0.03 cm(2)/(V.s) and solar cell power conversion efficiency (PCE) of 5.1% were achieved for polymer P2.

The synthesis and physicochemical properties of a new class of BODIPY-based donor-acceptor π-conjugated polymers are presented. Solution-processed top-gate/bottom-contact (TG-BC) thin-film transistors on flexible plastic substrates exhibit air-stable p-channel activities with charge carrier mobilities as high as 0.17 cm(2) /V·s and current on/off ratios of 10(5) -10(6) , the highest reported to date for a BODIPY-based semiconductor. The results shown here indicate a significant charge-transport improvement (>10000×) in BODIPY-based polymeric semiconductors, demonstrating its potential in future organic optoelectronic applications.

In this paper we report on the TFT performance of new organic n-channel semiconductors exhibiting very large carrier mobilities (2-3 cm(2)/Vs for injket-printed TFTs, >10 cm(2)/Vs for single crystals), exceptional bias tress and thermal stress stability. Finally, flexible EPDs were fabricated using these materials.

New solution processable organic semiconductors, consisting of pyrromelitic, naphthalene or perylene bisimide core and triarylamine N-substituents, have been synthesized. All three compounds are electrochemically active and undergo quasi-reversible oxidation and reduction as evidenced by cyclic voltammetry investigations. The oxidation process involves the transformation of the triarylamine substituents into radical cations as proven spectroscopically and spectroelectrochemically. The reduction process occurs at the arylene bisimide core leading to the formation of a radical anion and eventually a dianion in the second step. These findings are in perfect agreement with the DFT calculations which show that in the synthesized molecules the HOMO orbital is located on the triarylamine moiety whereas the LUMO one on the bisimide core. In all molecules studied the electrochemically determined ionization potential (IP) is slightly higher than 5.0eV whereas in naphthalene and perylene derivatives the electron affinity (EA) is close to −3.9eV. These values fulfill the requirements for n-type (electron) semiconductors in air operating n-channel field effect transistors (FETs) as well as for p-type (hole) conductors in p-channel FETs. To verify whether the newly synthesized compounds exhibit the expected electrical transport properties all organic (CYTOP dielectric) test transistors were fabricated. All three semiconductors showed no field effect in the n-channel configuration. To the contrary, they could be used in p-channel FETs showing, in the saturation regime, the hole mobility approaching 10−4cm2V−1s−1 – the value which slightly exceeds that measured for low molecular weight, amorphous triarylamine semiconductors.

Organic thin-film transistor (OTFT) performance depends on the chemical characteristics of the interface between functional semiconductor/dielectric/conductor materials. Here we report for the first time that OTFT response in top-gate architectures strongly depends on the substrate chemical functionalization. Depending on the nature of the substrate surface, dramatic variations and opposite trends of the TFT threshold voltage (~±50 V) and OFF current (10(5)×!) are observed for both p- and n-channel semiconductors. However, the field-effect mobility varies only marginally (~2×). Our results demonstrate that the substrate is not a mere passive mechanical support.

In this work, an analytical model of the contact resistance in top gate/bottom contacts organic thin film transistors has been derived. It combines both current crowding mechanism and an original model of the vertical accumulation of charges between channel and back electrode.The experimental gate voltage dependency of the contact resistance has been found to be nicely reproduced by this model, without requiring any additional numerical simulations, empirical vertical resistivity formulas or specific injection/transport mechanisms. In addition, the experimental semiconductor thickness and metal work function dependencies of the contact resistance, not considered so far, have been found in excellent agreement with this model.