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Title: New organic semiconductors and crosslinking additives for enhanced device performance and stability
Author: Rumer, Joseph
ISNI:       0000 0004 5349 0197
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2014
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Organic electronics promises inexpensive devices with diverse applications ranging from grid-scale power generation to disposable packaging. This results principally from compatibility with solution-processed manufacturing methods such as printing with large-scale, flexible and light-weight substrates. Organic solar cells in particular offer an underexploited renewable energy solution to increasing energy demand and global warming. However, for organic photovoltaic (OPV) cells the current goal is now to stabilise commercially viable efficiencies of >10%, for >10 years. As exemplified in this thesis, a structure-properties-fabrication-performance paradigm exists, necessitating judicious molecular design alongside tailored and optimised device manufacturing processes. Structure-property relationships are illustrated in a systematic series of TPD-2T-based copolymers: a C1-branched side-chain promotes increased crystallinity and solid-state packing, compared to C2- or C3-branching. In contrast, fabrication-performance relationships are illustrated with P3EPT, an analogue of P3HT, which exhibits a higher Voc in coarse BHJ blend devices compared to P3HT, most likely due to adopting a different morphology on casting in the absence of PCBM. The total paradigm is explored with a new class of benzodipyrrolidone-derived semiconductors in OPV and OFET applications. The advance from phenyl- to thiophene-flanked units (BPPs to BPTs), with reduced torsional twisting, affords ambipolar charge transport and satisfactory charge carrier mobility. In addition, select dihydropyrroloindoledione (DPID)-based materials afford unencumbered OPV performance when processing with more environmentally benign solvents. Furthermore, enhanced OPV device performance is achieved with DAZH and PDCF3-based small molecule crosslinkers, which convey thermal stability to OPV blends, typically through the frustration of fullerene aggregation. These additives exhibit sufficient shelf-life and ease of handling, with non-invasive and scalable activation by UV light, emitting only inert nitrogen gas. Moreover, our DAZH additive affords an increase in as-cast device efficiency, stemming from its design.
Supervisor: McCulloch, Iain Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral