oa Conjugated Small Molecules And Polymers For Use In Next Generation Organic Photovoltaic Solar Cells

The United Nations 2010 Climate Change Conference in Cancun (The Cancun Agreements) reached a verdict on climate change as one of the greatest challenges of our time and that deep cuts in emissions are required to prevent its potentially devastating effects. Energy is currently a vital global issue given the likely depletion of current resources (fossil fuels) coupled with the demand for higher-performance energy systems. Today the world face an urgent need for renewable energy technologies; solar power—the direct exploitation of the ultimate energy source for nature and our planet—should be one of these. Organic electronics has made enormous scientific and commercial progress over the last 10 years, mainly driven by the potential of applications such as light-emitting diodes(OLEDS) for display and large area lighting, field effect transistors (OFETs) for flexible backplanes and e-paper and solar cells (OPV) for large area energy generation. Much of this work has been motivated by the fact that organic semiconductors can combine the superb mechanical and processing characteristics of plastics with a variety of printing techniques, enabling large-area, low-cost manufacturing. Bulk-heterojunction organic photovoltaic (BHJ OPV) cells are a potential competitor to amorphous silicon-based technologies. Because of the ready availability of carbon feedstocks and numerous and flexible synthetic pathways, organic compounds are attractive materials for solar cell applications. OPV cells have experienced tremendous progress in performance during the last three years, with power conversion efficiency (PCE) now routinely surpassing 9%, attracting industries to commercialize these high-tech devices. A promising strategy to improve the performance in FETs and OPVs has been the inclusion of fused aromatic heterocycles into the conjugated polymer backbone. One such fused heterocycle of considerable recent interest and promise, is dithienopyrrole (DTP). Low band gap co-polymers of N-alkylated or N-arylated DTPs show promise as the active components in OPV and FETs. However their device performance has been limited by the propensity for the DTP to be readily oxidised. In addition to limiting the ambient stability of FETs under operating conditions, the low ionisation potential of DTP containing polymers limits the available open circuit voltage available in bulk heterojunction OPV devices, thus limiting efficiency. In the light of this we were interested in developing analogues of DTP which would demonstrate improved oxidative stability, by replacement of the flanking thiophene groups with more electron deficient thiazole groups to produce a fused dithiazolopyrrole (DTzP). We have developed a route to novel dithiazolopyrrole monomers and incorporated them in donor acceptor co-polymers, they have been successfully co-polymerised with thiophene, selenophene, thienothiophene and bithiophene by microwave assisted Stille polycondensation. The resulting polymers exhibited small optical band gaps combined with low lying HOMO energy levels, high ionization potential and good solubility in most common organic solvents and show promise for use in optoelectronic devices. Further investigations into their photovoltaic performance are ongoing which would be coupled with industrial partners in Qatar.