New triphenylamine-based organic dyes for efficient dye-sensitized solar cells

We report here on the synthesis and photophysical/electrochemical properties of a series of novel triphenylamine (TPA)-based organic dyes (TPAR1, TPAR2, TPAR4, and TPAR5) as well as their application in dye-sensitized nanocrystalline TiO2 solar cells (DSCs). In the four designed dyes, the TPA group and the rhodanine-3-acetic acid take the role of the basic electron donor unit and the electron acceptor, respectively. It was found that introduction of a CH2CH- group into the TPA unit exhibited better photovoltaic performance due to the increase of the electron-density donor moiety and that introduction of a methine (-CHCH-) unit to the pi bridge resulted in a red-shift and broadening of the absorption spectrum due to expansion of the pi-conjugation system. Density functional theory (DFT) calculation indicated that the electron distribution moved from the donor unit to the electron acceptor under light irradiation, which means efficient intramolecular charge transfer. In particular, the DSCs based on TPAR4 showed the best photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 81%, a short-circuit photocurrent density (J(sc)) of 18.2 mA cm(-2), an open-circuit photovoltage (V-oc) of 563 mV, and a fill factor (ff) of 0.61, corresponding to an overall conversion efficiency of 5.84% under AM 1.5 irradiation (100 mW cm(-2)). This work suggests that the molecular-designed triphenylamine dyes are promising in the application of DSCs.