Molecular Design, Synthesis, Characterization And Properties Of Novel Pyridinium Inner Salts For Organic Photosensitizer

Organic photosensitive dyes not only exhibit high molar extinction coefficient, but also can be prepared and purified in easy procedures at low cost, thus causing scientists'widespread concern. Some of the organic photosensitive dyes have obtained good photoelectric conversion efficiency, and show good prospects for application in dye-sensitized solar cells (DSSC). This dissertation was focused on molecular design, synthesis, characterization and properties of novel organic photosensitive dyes, and carried out the research work as follows:1. Molecular design, synthesis, characterization and properties of novel multi-substituted conjugated pyridinium sulfonate inner salts for organic photosensitive dyesTen conjugated pyridinium dyes in combination with pyridinium sulfonate inner salt acceptor and different number of donor were synthesized via Knoevenagel condensation. The chemical structures of the organic dyes are characterized by NMR and HRMS spectra. The electronic absorption and emission spectral and electrochemical properties of the dyes were investigated. The results showed that the molar extinction coefficient of the tri-substituted pyridinium dyes are much higher than that of the mono-or di-substituted dyes, and have a wide absorption band.The photovoltaic properties of dyes A1, A2, A3, B3and D3, in which pyridinium sulfonate inner salt as electron acceptor and containing different number of substitutents, were tested. The pyridinium dye A1which containing mono-substituted donor has much better sensitizing ability than those dyes containing two or three electron-donating groups. By molecular simulation of the HOMO and LUMO energy levels and associated electronic molecular arrangement, it was found that the spatial structure of the dye played an important role in the photovoltaic properties of the dye. In the excited state, the donor in multi-substituted dyes not only transfered the electron to acceptor-pyridinium inner salt unit but also to the donor unit which linking at4-or6-position of the pyridine ring.2. Molecular design, synthesis, characterization and properties of novel pyridinium inner salts with different anchoring groups and different length of carbon chain for organic photosensitive dyesIn combination with N, N-diethyl aniline electron donor and vinyl conjugated bridge, five novel organic pyridinium dyes with different anchoring groups and different length of connecting carbon chain were synthesized. The spectral and electrochemical properties of the new compounds indicated good light-harvesting capacity, wide and strong absorption in visible light, and good electrochemical properties.The dyes were applied in dye-sensitized solar cells (DSSC). It was found that pyridinium carboxylate inner salt is superior to pyridinium sulfonate inner salt, and shortening length of the carbon chain which connecting pyridinium unit with anchoring group can improve the power conversion efficiency of the dye. Compared with the reported dye Al which with sulfonate (-SO3-) as the anchoring group, the photovoltaic properties of the dye CA1, which with carboxylate as anchoring group has greatly improved. Under the similar conditions, the photocurrent and photovoltage increased from0.23mA cm-2and0.45V (for Al) to4.40mA cm-2and0.65V (for CA1), and the solar energy-to-electricity conversion efficiency increased from0.04%to1.69%. CA1also gives much broader IPCE response and higher IPCE value. Compared to the N-carboxylate benzothiazolinium dyes reported in the literature, the photovoltage of CA1increased from0.50V to0.65V. When quinolinium inner salt was used as electron-withdrawing group instead of pyridinium inner salt, the photoelectric conversion efficiency of the dye decreased significantly, however, the IPCE response reached to700nm which may provide some information for the further study to broaden the dye photoelectric response.3. Molecular design, synthesis, characterization and properties of pyridinium inner salts with different electron donors for organic photosensitive dyesWith N-carboxylate pyridinium inner salt as the electron acceptor and a double bond (C=C) as the π-spacer, six novel pyridinium dyes were synthesized by introducing different structures of donors, such as triphenylamine, diphenylamine, phenothiazine, phenoxazine et al. The spectral and electrochemical properties of the dyes showed nice light-harvesting ability, wide and strong absorption in the400-600nm band, and good electrochemical properties.The photovoltaic properties of these dyes indicated that introducing large volume and non-planar electron donors can improve the photoelectric conversion efficiency of the dyes. The photovoltaic properties of CB1which containing a triphenylamine electron donor have been improved while compared with that of CA1, a dye with N, N-diethylamino aniline unit as the electron donor. At AM1.5100mW/cm2illumination, the photocurrent and photovoltage increased from5.00mA cm-2and0.63V to5.59mA cm-2and0.66V, the photoelectric conversion efficiency increased from2.05%to2.33%. Under the similar conditions, the N719gave a η value of5.45%, and dye CB1got43%of photoelectric conversion efficiency of N719.The aggregation of the dye molecules on the TiO2surface could be inhibited effectively by introducing alkyl chain into the electron-donating group which led to the improvement of solar energy to electricity conversion efficiency. Due to the presence of oxygen atoms, the phenoxazine group shows excellent electronic properties, and the dye CK1gets a77value of2.01%, and gives the widest IPCE response (reached to725nm) while compared to the other dyes synthesized in this chapter which broadened the PCE response of such dyes in the infrared region.4. Molecular design, synthesis, characterization and properties of novel pyridinium inner salts with different conjugate bridges for organic photosensitive dyesEleven novel pyridinium dyes, with N-carboxylate pyridinium inner salt as the acceptor, were synthesized by introducing different conjugate bridge such as thiophene, ethylenedioxythiophene, benzene ring, diethoxy-substituted phenyl et al. The absorption and emission spectral and electrochemical properties of the dyes were investigated, and the results showed that these kind of dyes have a broader spectral band and stronger absorption intensity in compared with the pyridinium dyes which containing double bond π-spacer, Moreover, all the dyes exhibited good electrochemical properties.Compared to the dyes with double bond as conjugate bridge, the photovoltaic properties of the dyes, which with thiophene or ethylenedioxythiophene as the π-spacer, decreased significantly, on the contrary, the photovoltaic properties improved for the dyes with benzene or diethoxy-substituted phenyl unit as the conjugated bridge. As a result, we have developed a better diethoxy-substituted phenyl π conjugation linker. Compared to dye CB1, the dye CP1gives broader IPCE response and higher IPCE value, its photocurrent and photovoltage increased from5.73mA cm-2and641mV to7.84mA cm-2and659mV, the photoelectric conversion efficiency increased from2.61%to3.47%. Under the similar conditions, the reference N719gets a η value of5.27%.5. Molecular design, synthesis, characterization and properties of novel pyridinium inner salts with diethoxy substituted phenyl unit as conjugated bridge and cyanoacrylic acid as the electron acceptor for organic photosensitive dyesWith the diethoxy substituted phenyl developed in the previous chapter as conjugate bridge and cyanoacrylic acid as the electron acceptor, five new photosensitive organic dyes were synthesized with different electron donors such as triphenylamine, phenoxazine, alkoxy modified triphenylamine et al. The spectral and electrochemical properties of the dyes showed good light-harvesting capacity, wide and strong absorption in the visible light with good electrochemical properties.The photovoltaic properties testing indicated that the photoelectric conversion efficiency of the dye S1P, which with diethoxy-substituted phenyl unit as π-spacer, has been improved, and its photocurrent and photovoltage increased from8.20mA cm-2and0.66V to9.16mA cm-2and0.71V when compared with TPC1which contained a phenyl conjugate spacer.When adopting diethoxy-substituted phenyl as the conjugated bridge, the photovoltaic properties were also affected by different electron donors. The dye SIP which with triphenylamine as the electron donor achieved a promising conversion efficiency of4.23%under AM1.5100mW/cm2illumination and had a high1PCE plateau of72%at420nm. Under similar experimental conditions, the N719dye gives a η value of5.90%. The dye S3O and S3P are adopted alkoxy chain modified aniline unit and N-pentyl phenoxazine unit as the electron donors, respectively. The photoelectric conversion efficiency of the two dyes kept at about4%, the maximum IPCE value is more than50%. Compared to the SIP, S3O and S3P give broader IPCE response, and reach to675nm and715nm, respectively.