Indolizine-based donors as organic sensitizer components for dye-sensitized solar cells

Strong electron-donating functionality is desirable for many organic donor-π-bridge-acceptor (D-π-A) dyes. Strategies for increasing the electron-donating 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-π-A π-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. Indolizines are exceptionally strong organic donor building blocks for use in D-π-A dyes for dye sensitized solar cells. A series of indolizine-based dyes is synthesized for comparison to known common organic donor functionality. These dyes are studied computationally, electrochemically, spectroscopically, and in dye-sensitized solar cell devices.