Revelation of Structure-Property Relationships of Polymers Using Molecular Simulation

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Environmental issues related to energy production from fossil fuels and soaring crude oil prices have been the main stimulants for the development of renewable energy resources. In fact, energy from one hour of sunlight striking on Earth is more than all of the energy consumed by mankind in an entire year and finding a suitable way to capture this form of energy could definitely solve energy concerns of the human race forever. Advent of organic semiconductors in the early 80s made it possible to fabricate solar cells from polymers. The advantages of these so-called plastic solar cells include lightweight, versatility of chemical structure, mechanical flexibility and ease of processing (inexpensive). However, there are still two major hurdles that need to be overcome and they are the power conversion efficiency (~ 8.3%, latest reported value) and durability (~ 1 year). It is expected that efficiencies of 10% or higher and device lifetimes of around 10 years will make this technology commercially viable. Most recently, preliminary results of various researchers have shown that conjugated di-block copolymers may help overcome the first hurdle as such materials exhibit a variety of controllable nano-scale morphology needed for high power conversion efficiency. To address both the power conversion efficiency and durability issues, I propose to use multiple tri-block copolymers. The basic idea is that beside the two blocks of the tri-block copolymers having the desired electronic properties, the third block will have strong affinity for the electrodes and/or transport layer and the ability to reduce the diffusivity of oxygen and water, the compounds that are believed to cause degradation of the active layer in polymer solar cells. Use of multiple tri-block copolymers will make the solar cell to absorb maximum portion of incident sunlight. In particular, I will apply molecular simulation techniques to study structure-property relationship of various tri-block copolymers. It is expected that insights generated in the proposed work will allow us to better design polymer solar cells.