Triphenylamine-based organic dyes with julolidine as the secondary electron donor for dye-sensitized solar cells

Two novel donor-donor-pi-conjugated-acceptor (D-D-pi-A) metal-free organic dyes (JTPA1 and JTPA2) with a julolidine moiety as the secondary electron donor for dye-sensitized solar cells (DSSCs) are synthesized. Their absorption spectra, electrochemical and photovoltaic properties are extensively investigated and compared with TPA2 dye. Transient absorption measurements show that both sensitizers are quickly regenerated and the dye cations are efficiently intercepted by the redox mediator. Both dyes show good performance as DSSC photosensitizers. In particular, a DSSC using JTPA2 with rhodanine-3-acetic acid shows better photovoltaic performance with a short-circuit photocurrent density (J(sc)) of 9.30 mA cm(-2), an open-circuit photovoltage (V-oc) of 509 mV and a fill factor (FF) of 0.68, corresponding to an overall conversion efficiency (eta) of 3.2% under AM 1.5 irradiation (100 mW cm(-2)). Under similar test conditions, ruthenium-based N719 dye gives an efficiency of 6.7%. Compared to TPA2, the dye regeneration rate, the short-circuit photocurrent density and the conversion efficiency of JTPA2 are doubled by introducing a julolidine unit. Our findings show that the julolidine unit may be an excellent electron donor system for organic dyes harvesting solar irradiation. (C) 2013 Elsevier B.V. All rights reserved.