Indolizine-Based Donors as Organic Sensitizer Components for Dye-Sensitized Solar Cells

Strong electron-donating functionality is desirable for many organic donor-pi-bridge-acceptor (D-pi-A) dyes. Strategies for increasing the electrondonating strength of common nitrogen-based donors include planarization of nitrogen substituents and the use of low resonance-stabilized energy aromatic ring-substituted nitrogen atoms. Organic donor motifs based on the planar nitrogen containing heterocycle indolizine are synthesized and incorporated into dye-sensitized solar cell (DSC) sensitizers. Resonance active substitutions at several positions on indolizine in conjugation with the D-pi-A pi-system are examined computationally and experimentally. The indolizine-based donors are observed to contribute electron density with strengths greater than triarylamines and diarylamines, as evidenced by UV/Vis, IR absorptions, and oxidation potential measurements. Fluorescence lifetime studies in solution and on TiO2 yield insights in understanding the performance of indolizine-based dyes in DSC devices.