Engineering morphology in small molecule organic photovoltaic cells for efficient exciton diffusion and dissociation

Saturday, November 1, 2008 - 1:00pm - 1:30pm
EE/CS 3-180
Russell Holmes (University of Minnesota, Twin Cities)
Organic materials are attractive for application in photovoltaic cells due to their compatibility with lightweight, flexible substrates, and high-throughput processing techniques. Optical absorption in these materials leads to the creation of a bound electron-hole pair known as an exciton. The exciton is mobile, and diffuses to a heterojunction where electron-hole dissociation and photocurrent generation may take place. In most organic materials, the exciton diffusion length is much shorter than the optical absorption length. This “exciton bottleneck” limits the active layer thickness and reduces the absorption efficiency of the cell. Routes around the bottleneck have centered on the use of mixed donor-acceptor morphologies to increase the area of the dissociating interface. While promising, these architectures are difficult to optimize, and can introduce resistance for the collection of photogenerated carriers. This talk will examine an alternate approach to overcome the exciton bottleneck, focusing on the use carefully controlled, graded morphologies in organic photovoltaics.
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