Synthesis And Photovoltatic Performances Of Rigid Triarylamine Sensitizers For Dye-sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) have been considered as a promising, sustainable and environmental friendly energy device to meet the demands of mankind in the future. Compared with metal complexes, the metal-free sensitizers have also attracted considerable scientific attention due to their low cost, facile structural modifications, easier preparation and purification. The critical issue in dye-sensitized solar cells is to improve the Jsc, Voc and photovoltaic properties of the solar cells. Series of new organic D-A-π-A sensitizers containing benzotriazole or benzothiadiazole as auxiliary electron withdrawing units have been synthesized. Their photophysical, electrochemical and photovoltaic properties have been studied in this paper.In chapter1, the structure, working principle and related parameters for the dye-sensitized solar cells have been introduced. Recent researches on new dye-sensitizers have been reviewed. Based on that, the research strategy and main research contents of the DSSCs is presented.In chapter2, three new organic D-A-π-A sensitizers DIA6-DIA8containing benzotriazole (BTZ) as auxiliary electron withdrawing units and rigid triarylamine as donor have been synthesized. As a result, the BTZ bearing long alky chain can broaden the absorption spectra of dye, increase the value of Jsc, inhibit the charge recombination of DSSCs, thus result in improving the photoelectric conversion efficiency of DSSCs. The photoelectric conversion efficiency of DIA6based device has been increased by27%compared to DIA2based device. Based on that, DSSCs with one dye containing BTZ and thieno[3,2-b]thiophene as the π-spacer (DIA7) showed the highest open circuit voltage (Voc=829mV). The addition of one more thiophene unit to DIA6broadens the absorption spectra, leading DIA8device to produce the largest photocurrent. Among these sensitizers, the best photovoltaic performance was obtained by DIA8device:a short circuit photocurrent density (Jsc) of13.45mA cm-2, an open-circuit photovoltage (Vco) of757mV, and a fill factor (FF) of70%, corresponding to an overall conversion efficiency (η) of7.15%.In chapter3, three new organic D-A-π-A sensitizers DIA5, DIA9-DIA10containing benzothiadiazole (BTD) as auxiliary electron withdrawing units and rigid triarylamine as donor have been synthesized. As a result, compared with DIA6, the absorption spectra of DIA9has been red shifted by42nm and the Voc of DIA9has decreased by72mV, indicating that different auxiliary electron withdrawing units influence the DSSCs performance in different way. Owing to long alky chain, the Voc of DIA9device has been improved by72mV compared to DIA5, implying that the alky chain can slow the charge recombination of DSSCs. However, the long alky chain also causes huge steric hindrance, which can break the plane of dye molecule and decrease the absorbed amount of dye on the TiO2, result in the decrease of Jsc. The Jsc value of DIA10based device with broaden absorption spectra has been limited due to the less absorbed amount on TiO arised from the twisted molecule. According to that, it is a good design for the D-A-π-A structured dyes to avoid the long alkyl chain tightly close to the acceptor.