We report the synthesis of a selenophene -diketopyrrolopyrrole monomer and its co-polymerisation with selenophene and thieno [3,2-b]thiophene monomers by Stille coupling. The resulting low band gap polymers exhibit ambipolar charge transport in organic field effect transistors. High and balanced electron and hole mobilities in excess of 0.1 cm 2 V -1 s -1 were observed in bottom gate, bottom contact devices, 10 suggesting that selenophene inclusion is a promising strategy for the development of ambipolar organic semiconductors.

ABSTRACT:We report the synthesis of a novel ladder-type fused ring donor, dithienogermolodithiophene, in which two thieno [3,2-b]thiophene units are held co-planar by a bridging dialkyl germanium. Polymerisation of this extended monomer with N-octylthienopyrrolodione by Stille polycondensation afforded a polymer, pDTTG-TPD, with an optical band gap of 1.75 eV combined with a high ionization potential. Bulk heterojunction solar cells based upon pDTTG-TPD:PC71BM blends afforded efficiencies up to 7.2% without the need for thermal annealing or processing additives.There has been significant recent progress in the development of conjugated polymers for use in organic field effect transistors and bulk heterojunction (BHJ) polymer solar cells. 1 One promising class of polymers for these applications are the so-called ladder polymers 2 , in which linked aromatic units such as thiophene or benzene are forced to be coplanar and fully conjugated by the use of bridging heteroatoms. 3 The enforced co-planarity reduces rotational disorder thereby lowering reorganization energy and potentially increasing charge carrier mobility. 4 The bridging atoms also serve as a point of attachment for the necessary solubilizing groups needed to ensure processable materials.Within the class of donor-acceptor ladder polymers, bridged bithiophenes have proven to be a particularly useful building block. For example donor-acceptor type copolymers of cyclopentadithiophene (a C bridge) with 2,1,3-benzothiadiazole have exhibited FET mobilities up to 3.3 cm 2 V -1 s -1 when substituted with long hexadecyl sidechains. 5 The incorporation of bulky 2-ethylhexyl sidechains affords a more amorphous polymer, which nevertheless showing promising BHJ efficiencies of 5.5% when processed from solutions with high boiling additives. 6 Changing the bridging heteroatom from C to Si (dithienosilole) or Ge (dithienogermole) for analogous benzothiadiazole co-polymers enhances crystallinity, leading to improved charge transport and a reduction in bimolecular recombination. 7 The improvement in crystallinity has been rationalised on the basis of the longer C-Si/Ge bond compared to the C-C bond, which alters the geometry of the fused heterocycle facilitating enhanced intramolecular interactions. 8 In addition the replacement of the C bridge with Si or Ge alters the electronic energy levels of the resultant polymers, generally resulting in a lowering of both the HOMO and LUMO. This has been rationalized by interaction σ* orbital of the silylene/germylene fragment with the π* orbital of the aromatic system. Based upon the promising performance of these bridged dithiophene monomers, we were interested to further extend the conjugation length of the monomer and improve its coplanarity by the incorporation of fused thieno[3,2-]thiophene (TT) instead of thiophene. 10 Thieno[3,2-b]thiophene has been widely utilized as a co-monomer in a variety of high performing polymers, where it has been shown to promote intrachain packing and improve charge carrier mobility. 11 In add...

Although the performance of organic thin-film transistors (OTFTs) has increased significantly over the last decade, it still remains challenging to fabricate large area arrays of transistors with good device-to-device parameter uniformity.[1] Approaches based on the use of solution processable organic semiconductors are attractive, both in terms of throughput and the ability to pattern the semiconductor directly onto a range of substrate materials such as plastic. In terms of organic semiconductors, both soluble small molecules and polymers are viable materials classes with the former often being advantageous in terms of the higher charge carrier mobilities that can be obtained in OTFTs. Despite this significant advantage, however, the processing of highly crystalline small molecules into uniform thin films over large area substrates is often much more challenging than polymers, especially with respect to

Molecular doping of organic semiconductors and devices represents an enabling technology for a range of emerging optoelectronic applications. Although p‐type doping has been demonstrated in a number of organic semiconductors, efficient n‐type doping has proven to be particularly challenging. Here, n‐type doping of solution‐processed C60, C70, [60]PCBM, [70]PCBM and indene‐C60 bis‐adduct by 1H‐benzimidazole (N‐DMBI) is reported. The doping efficiency for each system is assessed using field‐effect measurements performed under inert atmosphere at room temperature in combination with optical absorption spectroscopy and atomic force microscopy. The highest doping efficiency is observed for C60 and C70 and electron mobilities up to ≈2 cm2/Vs are obtained. Unlike in substituted fullerenes‐based transistors where the electron mobility is found to be inversely proportional to N‐DMBI concentration, C60 and C70 devices exhibit a characteristic mobility increase by approximately an order of magnitude with increasing dopant concentration up to 1 mol%. Doping also appears to significantly affect the bias stability of the transistors. The work contributes towards understanding of the molecular doping mechanism in fullerene‐based semiconductors and outlines a simple and highly efficient approach that enables significant improvement in device performance through facile chemical doping.

Keywords: Schottky diode, radio frequency diodes, RFID, nanogap electrode, 13.56 MHz Main TextRadio Frequency Identification (RFID) is a rapidly growing technology used for wireless communication and the identification of objects in close proximity through radio waves. [1] Although already a billion dollar industry [2] , RFID technology promises substantial further growth by adopting fully printable processing routes. However, there remain several bottlenecks to be overcome before this opportunity can be realised, particularly pertaining to the high frequency performance of printable electronics.RFID tags are generally composed of a coupling element, or antenna, a direct current (DC) rectifier and integrated circuitry (IC). The rectifying element is by far the most important component in terms of high-frequency (HF) operation, as the logic may take place at much J. Semple et al., Small (2016), DOI: 10.1002/smll.201503110 2 lower frequencies than the RF base carrier frequency. Different frequency bands exist for different applications, though the current target for printable RFID is the widely employed 13.56 MHz band. [1] Conventionally, complementary metal-oxide-semiconductor (CMOS) technology favours the use of diode-connected metal-oxide-semiconductor field-effect transistors (MOSFETs) for rectification within this element. However, Schottky diodes, with their inherently lower voltage operation, lower series resistance and exponential currentvoltage relationship offer a superior choice for rectifiers. [4] There has been extensive work carried out in recent years to develop high frequency organic Schottky diodes following the pioneering work of Steudel et al. who demonstrated pentacene-based Schottky diode rectifiers operating at 50 MHz. [5] More recently C60-basedSchottky diodes with a cut-off frequency (fCO) up to 0.7 GHz have also been reported. [6] Diodes based on metal oxide materials (particularly In-Ga-Zn-O) have recently emerged as a promising material, demonstrating device performance up to and above 1 GHz. [7][8][9] Despite such promising results, manufacturing of these conventional staggered diodes relies on vacuum processing, which renders them incompatible with cost-effective large-volume product integration. To address this important bottleneck, recent work has been devoted to solutionprocessable organic diodes with adequate performance. [10][11][12] Si nanoparticles have recently been demonstrated as a potential route to solution processed diodes with cut-off frequencies as high as 1.6 GHz.[13] However, demonstrating high yield manufacturing of solution-processed diodes with cut-off frequency 50 MHz still remains a significant challenge.The operational frequency of Schottky diodes is inversely proportional to the product of the series resistance (RS) and junction capacitance (Cj). A common approach to boosting the device cut-off frequency is by reducing RS through the use of a high charge carrier mobility J. Semple et al., Small (2016) However, there are inherent problems with implementing...