Study On The Application Of Octacarboxy-Phthalocyanine Dyes In Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) have been attracting widespread scientific and technological interest since O’Regan and Gratzel reported their pioneering work in1991. Owing to their high efficiency for the photoelectric conversion and low production cost, DSSCs have evolved as potential alternatives to traditional photovoltaic devices in the past two decades. The photoelectric conversion efficiency is the key issue for their practical applications. In this subject, the performance of phthalocyanine-sensitized cells was systematically studied through coadsorption of attapulgite nanoparticles, as well as the introduction of metal nanoparticles and the wider spectral response range of dye. As a result of these new methods improved the photoelectric conversion efficiency of DSSCs.In this thesis, a series of octacarboxy-metallophthalocyanine dyes, i.e., MgOCPc, MnOCPc, FeOCPc and ZnOCPc with variant3d orbitals (3d0,3d5,3d6, and3d10, respectively) were designed and synthesized by microwave irradiation. The structures of the dyes were characterized by IR spectra, UV-visible spectra,1H and13C NMR spectra. The thermal, photophysical and elctrochemical properties of four dyes were studied. DSSCs were constructed based on these dyes and detailed relationship between dye structures and photovoltaic performance was investigated. The results showed that FeOCPc had excellent thermal property with a highest decomposition temperature (504℃), and ZnOCPc had a highest molar extinction coefficient (4.07×104M-1cm-1). The redox potentials of ground and excited states of FeOCPc and ZnOCPc matched well with that of electrolyte (I-/I3-) and TiO2conduction band, respectively. DSSC device based on ZnOCPc exhibited a best photovoltaic properties with an open circuit voltage(Voc) of0.429V, a short circuit photocurrent density (Jsc)of0.409mA cm-2and the photoelectric conversion efficiency (η) of0.13%under AM1.5irradiation (100mW cm-2) when comparing to the other three dyes.Phthalocyanines as photosensitizers for DSSCs have obtained unimpressive photoelectric conversion efficiencies because of strong aggregation blocking transmission channel of photo-generated charge carriers. The effects of attapulgite nanoparticles (AT) as coadsorbent on the photophysical and photovoltaic properties of DSSCs based on ZnOCPc were investigated. It was found that the coadsorbent of AT can hinder effectively dye π-π aggregation and improve electron injection and thus Jsc. When AT content was10mg (dye solution,50ml), the parameters of photovoltaic performance reached the maximum. Meanwhile, the electrochemical impedance spectroscopy (EIS) indicated that AT decreased the charge-transfer resistances at the TiO2/dye/electrolyte interface. It was worth noting that, the resistance of DSSC with10mg AT was smaller than that of other DSSCs.Surface plasmon resonance from silver nanoparticles has been applied to increase the optical absorption and photocurrent in DSSCs. Ag/AT nanocomposites was preparation by chemical reduction for the application in DSSCs. The structure of the nanocomposites was characterized by field emission scanning electron microscope (FESEM), X-ray spectroscope (EDS) and X-ray diffraction (XRD). The spectra absorption of TiO2electrodes and the photovoltaic performance of DSSCs with different size distribution of Ag/AT nanocomposites were studied. In addition, the nanocomposites distributed in the TiO2electrodes surface were observed through the FESEM. The nanoparticle sizer test revealed that Ag/AT nanocomposites were endowed with the minimum size of591nm which corresponded to the strongest spectral absorption and highest photocurrent, under the molar ratio of glucose and silver nitrate being2. However, the bigger nanocomposites formed nano-sized Ag clusters in TiO2electrode.In order to expand the spectrum absorption of phthalocyanine, improve the efficiency of intramolecular charge transfer, nature dye, lutein was introduced into DSSCs. The geometrical structures of lutein and ZnOCPc were optimized by performed density functional theory (DFT) calculations at the GGA/PBE level with Materials Studio5.0program package. The electron distribution of HOMO-2, HOMO-1, HOMO, LUMO+1, LUMO+2were investigated. Theoretical calculation results showed HOMO/LUMO energy level of lutein and ZnOCPc was consistent with experimental values. The effects of various mole ratios ZnOCPc/lutein on the photophysical and photovoltaic properties, intramolecular charge transfer behavior and electron lifetime of co-sensitization cells were systemically investigated. Lutein and ZnOCPc dyads co-sensitization gave a remarkable increase in the photocurrent and enhanced the overall conversion efficiency of the DSSCs compared with that of an individual dye used DSSCs. The cell obtained a highest tj (η=0.29%) and lowest resistance at the TiO2/dye/electrolyte interface, when ZnOCPc/lutein mole ratio was4:1.