Spectral Broadening via Vinylene Copolymers for Bulk Heterojunction Polymer Solar Cells

Organic photovoltaics have shown promise as a platform for low cost solar energy conversion. Polymer based solar cells have the potential to be implemented as lightweight, flexible solar cells that can be incorporated into existing infrastructure with minimal environmental impact. Currently, polymer-fullerene bulk heterojunction solar cells serve as the state-of-the-art in this area with efficiencies as high as 8%. A multitude of techniques are being explored to improve the performance of polymer solar cells even further. One area of interest is to improve the spectral overlap of the polymer absorption with the solar spectrum. Most polymers used in solar cells have band gap energies of more than 1.8 eV, which gives a poor overlap. As such, approaches toward lower band gap polymers are of great interest. Here a project is described, which is focused on reducing the band gap of thiophene polymers and copolymers via the incorporation of vinylene comonomers. Literature precedent supports this as a potentially general strategy to lower polymer band gaps. Here synthetic efforts toward this end and polymer characterization data are described.