Synthesis Of Aromatic Amine-based D-A-Ï€-A Organic Sensitizers And Applied In Dye-Sensitized Solar Cells

Dye-Sensitized Solar Cells (DSSCs) is a type of solar cells which convert light to electricity by means of harvesting the solar irradiation by the sensitizers. DSSCs have attracted great worldwide attention due to their considerable efficiency and low cost, in which the sensitizer is deemed as the crucial component. To achieve high efficiency, the organic dyes are usually required to possess high charge carrier mobility, broad and intense spectral absorption and high stability. In this paper, several series of sensitizers have been designed and synthesized. Their photovoltaic performances have been studied in detail. In addition, a novel anchoring group of pyridine has been introduced into the organic dyes and has been studied.In chapter1, the definition of the structure and principle for the dye-sensitized solar cells, nanoporous semiconductor electrode, electrolytes and counterelectrode are introduced. Recent researches of D-A-π-A dye-sensitizers have been reviewed. Then the research strategy of the dissertation is presented.In chapter2, six new D-A-π-A sensitizers (ID1-ID6), withtriarylamine as the electron donor; isoindigo as an auxiliary electron withdrawingunit; thiophene, furan, and benzene as the linker; and cyanoacrylic acid as theanchoring group, were synthesized through simple synthetic procedures and with low cost. Their absorption spectra were broad with long wavelengthabsorption maximum approximately at589nm and the absorption onset at720nm on the TiO2film. Electrochemical experiments indicate that the HOMOand LUMO energy levels can be conveniently tuned by alternating the donormoiety and the linker. All of these dyes performed as sensitizers for the DSSCstest under standard global AM1.5solar light condition, and a maximum overall conversion efficiency of5.98%(Jsc=14.77mA cm-2, Voc=644mV,ff=0.63) is obtained for ID6-based DSSCs when TiO2films were first immersed for6h in20mM CDCA ethanol solution followed by12h of dipping in the dye CH2CI2solution. Electrochemical impedance measurement data implies that the electron lifetime can be increased bycoadsorption of CDCA, which leads to a lower rate of charge recombination and thus improved Voc.In chapter3, a series of new D-A-π-A organic dyes (ID7-ID9) containing indoline as electron donor have been synthesized, characterized, and used as the sensitizers for dye-sensitized solar cells (DSSCs). The influence of the donor and the2-ethyl-hexyl chain on isoindigo sensitizer and cell efficiency was studied. In comparison with the model dye ID1, these dyes containing indoline donor display broader absorption spectrum and higher molar extinction coefficient, which would enhance the short-circuit photocurrent density. Attaching the2-ethyl-hexyl chain in the middle of the isoindigo proved to be an effective means for reducing the π-π aggregation of the dyes on TiO2. Moreover, the steric hindrance of the banched chain successfully suppressed charge recombination and improved the open-circuit voltage. As a result, ID7-based DSSCs achieved a high overallconversion efficiency of5.83%(Jsc=13.58mA cm-2, Voc=602m V,ff=0.71) under standard global AM1.5solar light condition.In chapter4, a series of new pyrido[3,4-b]pyrazine-based organic sensitizers (PP-I and APP-I-IV) containing different donors and π-spacers have been synthesized and employed in dye-sensitized solar cells (DSSCs). It was found that APP-Ⅳ based DSSCs with liquid electrolyte display the highest power conversion efficiency (PCE) of7.12%. Importantly, a PCE of6.20%has been achieved for APP-IV based DSSCs with ionic-liquid electrolytes and retained97%of the initial value after continuous light soaking for1000h at60℃. This renders these pyrido[3,4-b]pyrazine-based sensitizers quite promising candidates for highly efficient and stable DSSCs.In chapter5, a series of new D-A-π-A sensitizers (OPP-Ⅰ-Ⅲ), with triarylamine as the electron donor, pyrido[3,4-b]pyrazine as the additional acceptor, thiophene and benzene as the linker and cyanoacrylic acid as the acceptor moiety has been synthesized to further improve the efficiency. The replacement of a methoxy group with anoctyloxy group can effectively reduce the π-π aggregation of the dyes on TiO2. Moreover, the steric hindrance of the octyloxy group successfully suppressed charge recombination and improved the open-circuit voltage (about80mV). OPP-Ⅰ-sensitized cell showedthe best conversion efficiency (PCE) of6.57%(Jsc=11.70mA cm-2, Voc=717m V, ff=0.78) under standard global AM1.5solar light condition.In chapter6, a series of new D-A-π-A sensitizer (PT1-PT4) containing [1,2,5]thiadiazolo[3,4-c]pyridine moiety were synthesized and used for dye-sensitized solar cells (DSSCs). Their absorption spectra, electrochemical and photovoltaic properties were fully characterized. Electrochemical measurement data indicate that the tuning the LUMO and HOMO energy levels can be conveniently accomplished by alternating the donor moiety. All of these dyes performed as sensitizers for DSSC test, PT2-sensitized cell treated with20mM CDCA showed the best conversion efficiency (PCE) of6.11%(Jsc=12.61mA cm-2, Voc=668mV, ff=0.74) under standard global AM1.5solar light condition.In Chapter7, a new anchoring group of pyridine (picolinonitrile) was introduced into the organic dyes, and four new dye sensitizers PY1-PY4were synthesized. Their absorption spectra, electrochemical and photovoltaic properties were fully characterized. The effect of the cyano group on photovoltaic performance was investigated. All of these dyes performed as sensitizers for DSSC test, PYl showed the best conversion efficiency (PCE) of2.14%(Jsc=6.49mA cm-2, Voc=509mV, ff=0.65) under standard global AM1.5solar light condition. Cyano-substituted pyridine dye (PY2) has a higher short-circuit current but the total value of the PCE is slightly lower than PYl because the open circuit voltage of PY2decreased, the further optimization is in progress.