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.