Lithographically defined nano-morphology in polymer-fullerene solar cells towards high efficiency

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The objective of this research is to develop an optimal morphology of vertically bi-continuous donor and acceptor materials interpenetrating into each other to achieve high efficiency in organic solar cells. This morphology decouples absorption depth from diffusion length, allowing effective exciton diffusion to large interfacial areas as well as vertical charge transport with reduced recombination. Intellectual merit: The proposed nanoimprint lithography with innovative mold technologies provides a practical means with greater precision than currently available techniques to make an optimal solar cell design. The thermal imprinting process can also induce favorable polymer chain alignment and crystallization, leading to higher hole mobility and light absorption. By decoupling absorption depth from diffusion length, a thicker polymer film than in conventional bulk heterojunction devices can be used to enhance light adsorption considerably. This morphology provides a basic nano-platform to study the interrelated polymer properties (crystallinity, mobility, chain orientation, stability, thermal dynamic properties, etc) and their correlation with geometry, imprint temperature, surface effects, and device quantum efficiency. Broader impacts: This study will establish a comprehensive understanding of the effects of heterojunction nano-morphology on material properties and device characteristics, which is transformative to other materials and devices. What may naturally follow is the demonstration of 7-12% PCE in polymer solar cells. This research will be integrated with education through available programs at UTD to provide research opportunities for students. Particularly, this program aims to bring greater nanotechnology exposure to a broad range of individuals including undergraduates and the education community on the whole.