New Triphenylamine-Based Dyes for Dye-Sensitized Solar Cells

A series of new conjugated metal-free organic dyes (TC1, TC2, TC3, and TC4) comprising triphenylamine (TPA) moieties as the electron donor and cyanoacetic acid moieties as the electron acceptor/anchoring groups were designed at the molecular level and developed for the use in dye-sensitized solar cells (DSCs). Quantum chemical calculations have been performed to gain insight into structural, electronic, and optical properties of the as-synthesized sensitizers. The time-dependent density functional theory calculations allowed assignment of the experimental spectroscopic data. It is found that the photovoltaic performance of the DSCs with the as-synthesized dyes can be improved by enhancing the electron-donor ability and extending the π-conjugated bridge of the dyes. In particular, the DSCs based on 2-cyano-5-(4-(phenyl(4-vinylphenyl)amino)phenyl) penta2,4-dienoic acid dye (TC4) showed an open circuit voltage of 652 mV, a short circuit photocurrent density of 11.5 mA cm-2, and a fill factor of 0.64, corresponding to an overall light to electricity conversion efficiency of 4.82% under AM 1.5 irradiation (100 mW cm-2). This result reveals that efficient electron injection from the excited sensitizer to the conduction band of titania film occurs, owing to the more delocalizing electrons of the bridge and donor part of the dyes.