Research in the Luscombe group focuses on the synthesis (projects 1-3) and applications of organic electronic polymers (projects 4-6).For most up-to-date information about our research, go to out publications page. Please refer to the Advanced Materials for Energy (AME) Institute website for University wide energy-related initiatives. The Luscombe group is also a member for the NSF Center for Stereoselective CH Functionalization and the Molecular Engineering and Sciences Institute.
1. Quasi-living polymerization of semiconducting polymers The ability of chemists to design and synthesize conjugated polymers with precise control over the molecular weight with narrow polydispersities remains the key to technological breakthroughs using polymeric and photonic devices. Being able to synthesize semiconducting polymers in a controlled manner will reduce the variability between synthetic runs which can lead to differences in electronic device performances between different research labs. We are investigating methods to perform controlled externally initiated polymerizations, and looking at ways to control the polymerization to ultimately create polymer brushes, star-shaped polymers, and block copolymers.Following on from our recent publications, we are further investgating the effect of varying the structure of the initiator species. Variation of the halide, phosphine ligand, and aryl group is being investigated which should allow insights into the mechanism of the polymerization and allow subsequent improvements in its control.Recent publications: Macromolecules, 2009, ASAP, DOI: 10.1021/ma90141k; J. Am. Chem. Soc, 2009, 131, 12894. 2. Synthesis of novel hybrid materials for organic photovoltaics We have developed a new method for the surface modification of CdSe nanocrystals which allows the introduction of covalently attached aryl groups. With this we are attempting to initiate the polymerization of a thiophene monomer on the surface of the nanocrystal resulting in a completely conjugated inorganic-organic hybrid material. The direct attachment of a P3HT chain should facilitate charge separation at the inorganic-organic interface resulting in higher power conversion efficiencies. 3. Synthesis of n-type polymers In advancing the research and development of electronic devices created from organic semi-conducting materials, Matt is exploring the synthesis and design of n-type organic polymers for use in field-effect transistors, photovoltaic materials, and various other applications. The field of organic n-type semi-conducting materials is a lesser developed one by comparison to organic p-type materials which are quite heavily investigated largely due to issues of material insolubility in volatile organic solvents faced by the former. New breakthrough developments in n-type material research are heavily lagged behind complementary p-type materials which Matt strives to change by specifically investigating materials based off heteroatom aromatic-ring containing molecules such as the various polymers that can be made from derivatives of functionalized naphthalene.4. Nanostructured electrodes for organic photovoltaic devices Tricia researches nanostructured electrodes in organic photovoltaics. Nanostructured electrodes and nanogaps are fabricated using electron beam lithography and oblique angle deposition, respectively. These unconventional device architectures are designed to affect such processes as photon harvesting, exciton (electron-hole pair) separation and charge transport in organic semiconductors. Experiment and models are coupled to determine the effects of static electric fields and near field optics in these structures, while systematically tuning the geometry and electrode materials to optimize the devices.5. Polymer nanowires for organic photovoltaic devices While there are many advantages to organic photovoltaics (OPVs), several issues remain that need to be addressed before they can be widely produced and used. The most pressing of these problems is the relatively low power conversion efficiency yielded by organic devices. Currently, the most efficient OPVs are about five times less efficient than their inorganic counterparts. These lower efficiencies are largely resultant of exciton recombination. Once generated within the active layer of an OPV, excitons have the ability to travel only about 10nm before recombination is likely to occur. This distance is much less in organics than it is in inorganic materials.
A novel approach to overcoming this problem involves using nanowires of P3HT dispersed within a matrix of PCBM in the active layer of the OPV. These nanowires increase the interfacial area between the P3HT and PCBM domains. It is hoped that by influencing the size of the nanowires, we can obtain a more optimized device structure. Tailoring nanowire radii to ~20nm will create domains on scale with exciton dissociation and should produce a dramatic decrease in excition recombination.
By altering the concentration of P3HT in solution and adjusting the cooling rate during nanowire self assembly, we have demonstrated statistically significant changes in average nanowire radius and surface coverage. Additionally, these nanowires have been successfully incorporated into the active layer of OPVs, producing devices with PCEs greater than 2%. Ongoing goals of this project center on increasing the ability to exploit nanowire size, devloping a fuller understanding of nanowire growth, and optimizing processing techniques to enable the construction of higher efficiency devices. 6. Air stable semiconducting polymers for thermoelectricsThermoelectric materials can convert a temperature gradient into an applied voltage, or convert an electrical potential into a temperature difference. These properties allow thermoelectric materials to operate as temperature driven electrical power generators and heater/coolers. This type of electrical power generation can provide energy savings from a variety of sources including: used heat from the exhaust systems of cars, used heat from power plant exhaust, and used exhaust heat from incinerators. Thermoelectric generators might also power hand held electronic devices, such as cell phones, using body heat. Thermoelectric materials also have biological applications for potential use as power generators for pace makers and implants, as well as power generators for radio frequency tags used in animal studies. Currently, there has been a limited amount of study concerning the thermoelectric performance of polymers. Most semiconducting polymers are easy to oxidize, have poor heat resistance, and decompose at relatively low temperatures. Our group has synthesized a series of air stable semiconducting polymers which are robust enough for thermal measurements, and are potential candidates as thermoelectric materials. Research to determine the Seebeck coefficient (S), and the figure of merit (ZT), of these air stable polymers is in progress.