Photovoltatic Performances Of Iminostilbene Sensitizers For Dye-sensitized Solar Cells

Dye-Sensitized Solar Cells is a type of solar cells which convert light to electricity by means of harvesting the solar irradiation by the sensitizer. DSSCs have attracted great attention in the research field for its simple preparation, low cost and relatively high efficiency. The most important issue in dye-sensitized solar cells is to improve the conversion efficiency and stability of the solar cell. In this paper, the unit of iminostilbene was introduced into the sensitizer as a new electron donor. We propose a novel D-A-π-A model to construct new dyes by introducing electron-withdrawing groups, such as benzothiadiazole, quinoxaline and diketopyrrolopyrrole, into the π-bridge of traditional D-π-A organic dyes as the additional acceptor. The photovoltaic performances of the new sensitizers have been studied in detail. The structure-performance relationships, including donor, acceptor,π-bridge and alkoxy chains in D-A-π-Amodel are systematically investigated.In chapter1, the definition of the structure and principle for the dye-sensitized solar cells, nanoporous semiconductor electrode and electrolytes are introduced. Recent research of new dye-sensitizers have been reviewed.In chapter2, the dyes of IDB-1, ISB-1, IDB-2and ISB-2containing iminodibenzyl or iminostilbene as the electron donors, thiophene as the π-conjugation linkage, and cyanoacrylic acid as the electron acceptor were synthesized. The influence of iminodibenzyl or iminostilbene as the electron donors on the properties of sensitizers was studied. It was found that the dyes containing iminostilbene as the electron donor exhibited improved photovoltaic performance compared with the ones containing iminodibenzyl as the electron donor. A solar cell device based on the sensitizer ISB-2yielded a higher conversion efficiency of5.83%with a short circuit photocurrent density (Jsc) of13.14mA cm-2, an open-circuit photo voltage (Voc) of640mV, fill factor of0.68under100mW cm-2simulated AM1.5G solar irradiation.In chapter3, the dyes of S1, S2, S3and S4containing benzothiadiazole as additional electron-withdrawing unit, iminostilbene as the electron donor, thiophene or benzene as the π-conjugation linkage, and cyanoacrylic acid as the electron acceptor, termed the D-A-π-A configuration were synthesized. The influence of benzothiadiazole as additional electron-withdrawing unit on the properties of sensitizers was studied. It displays several advantages such as tuning of the molecular energy levels and red-shift of the charge-transfer absorption band. A solar cell device based on the sensitizer S2yielded a higher conversion efficiency of6.71%with a short circuit photocurrent density (Jsc) of13.69mA cm-2, an open-circuit photovoltage (Voc) of722mV, fill factor of0.67under100mW cm-2simulated AM1.5G solar irradiation.In chapter4, the dyes of Q1and Q2containing quinoxaline as additional electron-withdrawing unit, iminostilbene as the electron donor, thiophene or furan as the π-conjugation linkage, and cyanoacrylic acid as the electron acceptor, termed the D-A-π-A configuration were synthesized. The influence of quinoxaline as additional electron-withdrawing unit on the properties of sensitizers was studied. It displays several advantages such as tuning of the molecular energy levels and distinct improvement of photovoltaic performance and stability. A solar cell device based on the sensitizer Q2yielded a higher conversion efficiency of6.66%with a short circuit photocurrent density (Jsc) of12.89mA cm-2, an open-circuit photovoltage (Voc) of714mV, fill factor of0.72under100mW cm-2simulated AM1.5G solar irradiation.In chapter5, the dyes of DPP-1and DPP-2containing dike top yrro lop yrrole as additional electron-withdrawing unit, iminostilbene as the electron donor, thiophene as the π-conjugation linkage, and cyanoacrylic acid as the electron acceptor, termed the D-A-π-A configuration were synthesized. The influence of diketop yrro lop yrrole as additional electron-withdrawing unit on the properties of sensitizers was studied. It displays several advantages such as tuning of the molecular energy levels and red-shift of the charge-transfer absorption band. A solar cell device based on the sensitizer S2yielded a higher conversion efficiency of6.43%with a short circuit photocurrent density (Jsc) of11.89mA cm-2, an open-circuit photovoltage (Voc) of735mV,fill factor of0.73under100mW cm-2simulated AM1.5G solar irradiation.In chapter6, a couple of new D-A-π-A dyes H1and H2were designed and synthesized by introducing long alkoxy chains onto the additional electron-withdrawing unit benzothiadiazole and quinoxaline. The influence of diketopyrrolopyrrole as additional electron-withdrawing unit on the properties of sensitizers was studied. They display blue-shift of the charge-transfer absorption band. The solar cell devices based on the sensitizers H1and H2yielded conversion efficiency of5.85%and4.31%, respectively.