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A series of new push-pull organic dyes (BT-I-VI), incorporating electron-withdrawing bithiazole with a thiophene, furan, benzene, or cyano moiety, as π spacer have been synthesized, characterized, and used as the sensitizers for dye-sensitized solar cells (DSSCs). In comparison with the model compound T1, these dyes containing a thiophene moiety between triphenylamine and bithiazole display enhanced spectral responses in the red portion of the solar spectrum. Electrochemical measurement data indicate that the HOMO and LUMO energy levels can be tuned by introducing different π spacers between the bithiazole moiety and cyanoacrylic acid acceptor. The incorporation of bithiazole substituted with two hexyl groups is highly beneficial to prevent close π-π aggregation, thus favorably suppressing charge recombination and intermolecular interaction. The overall conversion efficiencies of DSSCs based on bithiazole dyes are in the range of 3.58 to 7.51 %, in which BT-I-based DSSCs showed the best photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 81.1 %, a short-circuit photocurrent density (J(sc)) of 15.69 mA cm(-2), an open-circuit photovoltage (V(oc)) of 778 mV, and a fill factor (ff) of 0.61, which correspond to an overall conversion efficiency of 7.51 % under standard global AM 1.5 solar light conditions. Most importantly, long-term stability of the BT-I-III-based DSSCs with ionic-liquid electrolytes under 1000 h of light soaking was demonstrated and BT-II with a furan moiety exhibited better photovoltaic performance of up to 5.75 % power conversion efficiency.

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Three metal-free bithiazole organic dyes (BTT-I-III) based on D-A-p-A building blocks were designed and synthesized for dye-sensitized solar cells (DSSCs) to study the influence of different electron donors on photovoltaic properties, in which the electron donors of BTT-I-III were carbazole, triphenylamine and indoline moieties, respectively. The UV/Vis absorption spectra of BTT-III containing indoline as electrondonor displayed red-shifted absorption compared to the other two dyes with an onset close to 700 nm.The incident photon-to-current conversion efficiency (IPCE) spectra of BTT-III showed a wide region and kept a value higher than 10-15% during 580-650 nm. Electrochemical measurement data indicated that the HOMO and LUMO energy levels could be tuned through introducing different electron-donors in the dye molecule. It was found that the overall conversion efficiency of indoline donor based dye BTT-III showed the highest efficiency of 7.86% under AM 1.5 irradiation (100 mW cm 22 ). The electron lifetime calculated from electrochemical impedance spectroscopy (EIS) measurement demonstrated the reduced charge recombination and the higher open-circuit voltage.