Synthesis and optoelectronic properties of dibenzofulvene based organic dyes for dye-sensitized solar cell (DSSCs)

Abstract

With the depletion of fossil fuels and the deterioration of environmental problems, solar energy has received much attention as one of the pro-environmental energy sources. Among the solar cells developed so far, compared with inorganic semiconductor solar cells, dye-sensitized solar cells have been widely concerned because of their low cost, low requirements on materials and processes, and high photoelectric conversion efficiency. Photosensitive dyes are used in dye-sensitized solar cells to absorb sunlight and inject excited-state electrons into the nano-semiconductor conduction band, so they are considered to be the core of DSSC. Whether it is possible to design and synthesize an organic dye with good photoelectric performance is a necessary prerequisite for the solar cell with high photoelectric conversion efficiency. Most non-metallic sensitizers have a D-π-A (Donor-π-Acceptor) sandwich structure because this structure can promote the conversion of electrons from D to A by inducing a π bridge, which promotes the possibility of photoelectric conversion. Therefore, we designed a series of diphenylamine derivatives as electron donors, dibenzofulvene groups as conjugated spacers, and cyanoacetic acid as an electron acceptor for organic dyes. In order to explore the relationship between structure and photoelectric conversion properties, organic dyes based on the dibenzofulvene group lie in 3, 6-substituted of single-electron acceptors and multi-electron acceptors were designed and synthesized. This thesis contains all the chemical synthesis methods, the preparation and detection methods of dye-sensitized solar cells that we have used. The results and discussion section showed the characterization of the nuclear magnetic resonance spectroscopy and mass spectrometry of the synthesized organic dyes and studied the photophysical and electrochemical properties of organic dyes. Moreover, theoretical calculations of intramolecular energy transfer and electron transfer were performed on the model of organic photosensitizing dyes. The results have shown that the structure of organic dyes is closely related to their photophysical and electrochemical properties. By adding a thiophene group as a π bridge and increasing the number of electron acceptors, the UV-vis absorption spectrum of the dye can be significantly red-shifted. The LUMO and HOMO levels of the designed organic dyes can simultaneously satisfy the potential requirements for the injection of exciting electrons into the TiO2 conduction band and dye reduction regeneration. The addition of a thiophene group as a π bridge also leads to an increase in the HOMO level, and the excited state electrons are more easily reduced, promoting more electrons into the TiO2 conduction band. Based on the optimization of the dye structure, the dye BPF3 have 3.49% of photoelectric conversion efficiency. It is expected that this study will further provide some useful references for the design, synthesis, and application of dibenzofulvene-based organic dye molecules in practice and theory.