Heterointerface control of organic semiconductor devices

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Organic electronic materials are widely used in LEDs, transistors and, though less advanced, in solar cells. Organic semiconductor devices are generally divided into two classes: those made by vacuum deposition of so-called 'small molecules' and those made by solution-processing of film-forming materials (typically polymers). The UK community, following some of the early work at Cambridge has tended to concentrate on the latter class of materials. The rationale for this is two-fold. Firstly, in terms of translation to large-scale manufacture, direct low-temperature solution processing of active semiconductors is very attractive for low-cost processing, particularly where patterning can be carried out by direct printing (ink-jet printing has been developed, for example, for deposition of red-, green- and blue-emitting materials in full colour displays). Secondly, solution processing presents challenges and opportunities for the formation of useful device structures. In some respects it is awkward - it is generally difficult to assemble multiple layers of organic semiconductor to make conventional laminar heterostructures because solvents are typically not sufficiently specific to allow successive layer depositions without disturbing lower layers - but in other respects, there are real opportunities to generate architectures that would be very difficult to make conventionally. For example, interpenetrating networks of electron-accepting and hole-accepting polymers are required for photovoltaic devices, so that light absorbed throughout the thickness of the semiconductor layer can generated excitons close enough to a region of heterojunction to generate separated charges. The rapid progress made over the last 10 years has taken the field to a level where device performance already sustains a fledgling industry. Basic understanding of the electronic structure of organic heterointerfaces both underpins this industry, and also presents us with a new landscape for discovery where we need to achieve a new level of control over molecular and nanoscale structure. Limitations in current device performance, for LEDs, PVs and FETs, are determined by limitations in our ability to control and measure structures at heterointerfaces. The vision of the present project is to achieve a step-change improvement in the control of molecular and nanoscale structure at organic heterointerfaces and thus to bring about a step-change in electronic functionality and performance of active semiconductor devices including LEDs, FETs and photovoltaics .The mining of this rich new seam of science will deliver game-changing discoveries for both science and engineering. The programme encompasses a variety of different interfaces, between organic-organic and organic-inorganic semiconductors; organic semiconductors and dielectrics; and organic semiconductor-electrode interfaces.