| With large consumptions of fossil energies and increasingly severer environmental pollution problems, the development of solar energy has been attracted more and more attentions of researchers all over the world. As a new photoelectric device, solar cells have broad development prospects. Among various solar cells, dye-sensitized solar cells (DSSCs) has become a research hotspot becasuse of its simple preparations, relatively low cost and high power conversation efficiency (PCE). As a key material of DSSCs, dye-sensitizers play an important role in light harvesting, electron generating, and injecting electrons into the conduction band of TiO2. Therefore, dye-sensitizers directly affect the PCE of DSSCs. Compared with metal complexes, organic sensitizers have some advantages, such as simple preparations, rich raw materials, high molar extinction coefficients. So it has achieve rapied development in recent years.Commonly, the structure of dye-sensitizer is Donor (D)-Conjugated linker (π)-Acceptor (A). The PCE of DSSCs can be enhanced by the structural modification of these three parts. In the paper, we have synthesized double-donor dyes DT-X series, which contains triphenylamine as donor, cyanoacetic acid as acceptor, and benzene or thiophene derivatives as conjugated linker. Additionally, single-donor dye ST-X series also have been synthesized for references. We’ve researched on the properties of dyes by increasing the amount of dye donors and prolonging its conjugated linkers. Details are as follows:1. Double-donor dyes DT-X series and reference dyes ST-X series have been designed and synthesized. MS, 1H NMR, and FT-IR were conducted to confirm the structures of target compounds and intermediates. Photophysical, photovoltaic, and electrochemical properties were also measured.2. The structure-property relationship have been investigated, including that increasing the amount of triphenylamine donors and prolonging conjugated linkers have an effect on photophysical and electrochemical properties. UV-Vis specta show that the absorption spectrum of ST-2 is blue shifted due to benzene added to the conjugated linker. When an additional triphenylamine donor was utilized to construct double-donor dye DT-1, the absorption spectrum is weaker in visible area. However, when thiopene is replaced by bithiophene to construct the conjugated linker, the absorption spectrum of DT-2 becomes stronger in visible section. According to electrochemical analysis, the LUMO energy levels of these dyes are higher than conduction band energy levels of TiO2; meanwhile, their HOMO energy levels are lower than I-/I3- oxidation-reduction potential. It means that the energy levels of these dyes meet the sensitizer energy requirements.3. Density functional theory (DFT) calculations show that electrons are mainly located at HOMO on ground state and LUMO on excited state. Excited electrons can transfer from donor to acceptor efficiently, then inject into TiO2 conduction band.4. Electrochemical impedance spectroscopy (EIS) and dye-loading tests have been conducted. It can be seen form EIS that DT-1 and DT-2 can effectively suppress electron combination and enhance open-circuit voltage of DSSCs due to increase the amount of triphenylamine donors. Dye-loading results show that, the dye-loading ability of DT-1 decreased with the increase of triphenylamine donor. However, the dye-loading ability of DT-2 and ST-2 increased with the extension of the conjugated linkers.5. The results of photovoltaic performances indicate that short-circuit current of ST-2 has been reduced due to introduce benzene into the conjugated linker in comparison to ST-1, resulting in a poor PCE. The additional triphenylamine donor can improve remarkably open-circuit voltage of DT-1, but which causes a decreasing short-circuit current, hence produces a lower PCE. Short-circuit current of DT-2 has been improved remarkably by replacing thiopene with bithiopene, thus better photovlotaic performances are obtained.
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