Efficient structural modification of triphenylamine-based organic dyes for dye-sensitized solar cells

A series of new organic D-g-A dyes, coded as DS-1, DS-2, DS-3, and DS-4, was designed, synthesized, and characterized by H-1 NMR, C-13 NMR, infrared spectroscopy, mass spectrometry, and elemental analysis. These dyes consist of a di(p-tolyl)phenylamine moiety as an electron donor, a cyanoacetic acid moiety as an electron acceptor/anchoring group, and different types of conducting thiophene units as electron spacers to bridge the donor and acceptor. It was found that both the use of di(p-tolyl)phenylamine donor and the variation of electron spacers in the D-pi-A dyes played an essential role in modifying and/or tuning physical properties of organic dyes. These dyes were developed as sensitizers for the application in dye-sensitized TiO2 nanocrystalline solar cells (DSSCs), and their photophysical and electrochemical properties were investigated. The DSSCs based on the dyes gave good performance in terms of incident photon-to-current conversion efficiency (IPCE) in the range of 400-700 nm. A solar-energy-to-electricity conversion efficiency (eta) of 7.00% was obtained with the DSSC based on 5-[[2-[p-(di-p-tolylamino)]styryl]thiophene-yl]thiophene-2-cyanoacrylic acid (DS-2) under simulated AM 1.5 G irradiation (100 mW/cm(2)): short-circuit current density (J(sc)) of 15.3 mA cm(-2); open-circuit voltage (V-oc) of 0.633 V; fill factor (FF) of 0.725. The density functional theory (DFT) calculation suggests that the electron-transfer distribution moves from the donor unit to the acceptor under light irradiation, which means efficient intramolecular charge transfer.