Synthesis and Photoelectric Properties of quinoxaline oriented Sensitizers with the multi anchoring groups for DSSC

Abstract

With the depletion of fossil energy and the deterioration of environmental problems, solar energy has received extensive attention as an environmentally friendly energy source. Among the solar cells developed so far, compared with inorganic semiconductor solar cells, dye-sensitized solar cells are increasingly subject to research due to their own low cost, high conversion efficiency, diverse molecular structure and easy modification. Photosensitive dyes play a vital role in dye-sensitized solar cells. They are considered to be the core of DSSCs in battery operation to absorb sunlight and inject excited-state electrons into the nano-semiconductor conduction band. Therefore, for a solar cell having high photoelectric conversion efficiency, it is a necessary precondition to be able to design and synthesize an organic dye having good photoelectric properties.

Most organic sensitizers have a D-π-A (Donor-π-Acceptor) structure because of no use of toxic or expensive metal and this structure can promote the conversion of electrons from Donor to Acceptor by inducing a πbridge, which promotes the possibility of photoelectric conversion. Therefore, we have designed a series of triphenylamine and phenothiazine derivatives for use as electron-donating groups, quinoxalines as electron-withdrawing groups, and carboxylic acid as electron acceptors for organic dyes. In order to explore the relationship between dye structure and photoelectric conversion performance, an organic dye based on quinoxaline was designed and synthesized. Triphenylamine and phenothiazine derivatives with alkoxy groups were introduced into the 2-position and 3-position of quinoxaline as a Y-shaped electron donor, carboxyl group were introduced at the 5-position and the 6-position used as an anchor group. In addition, it was expected that cyanoacrylic acid is introduced on the electron donor by π-spacer thiophene to increase the anchor group to optimize the dye structure and improve the photoelectric conversion efficiency.

With the depletion of fossil energy and the deterioration of environmental problems, solar energy has received extensive attention as an environmentally friendly energy source. Among the various solar cells currently being developed, compared to semiconducting inorganic solar cells, dye-sensitized solar cells are increasingly subject to research due to their own low cost, high conversion efficiency, diverse molecular structure and easy modification. Photosensitive dyes play a vital role in dye-sensitized solar cells. They are considered to be the core of DSSCs in battery operation to absorb sunlight and inject excited-state electrons into the nano-semiconductor conduction band. Therefore, for a solar cell having high photoelectric conversion efficiency, it is a necessary precondition to be able to design and synthesize an organic dye having good photoelectric properties.

This paper contains all the chemical synthesis methods we have used, the preparation and efficiency testing methods of dye-sensitized solar cells. Results and discussion section shows the NMR and mass spectrometric characterization of synthetic organic dyes and studied the ultraviolet absorption spectra and electrochemical properties of organic dyes. In addition, the intramolecular energy transfer and electron transfer are theoretically calculated on the model of organic photosensitive dyes. The results show that the structure of organic dyes is closely related to their photophysical and electrochemical properties. By increasing the number of anchoring groups, the photocurrent and stability of the dye is better. The LUMO and HOMO contents of the designed organic dyes can simultaneously meet the potential requirements for injecting excited electrons into the TiO2 conduction band and reducing dye regeneration. The addition of the thiophene group as a π bridge also leaded to an increase in the HOMO level, and the excited state electrons were more easily reduced, which promoted more electrons into the TiO2 conduction band, while the increase of cyanoacrylic acid as anchoring groups also promoted the dye in binding energy and electron injection rate on TiO2.

Based on the optimization of dye structure, the photoelectric conversion efficiency of dye TPQ1 was 3.45%, TPQ2 4.38% and TPQ3 4.58%, respectively, and the photoelectric conversion efficiency of dye TOQ4, TPQ5 and TPQ6 was 3.63%, 4.45% and 4.82%, respectively. It is expected that this study will provide theoretical and practical references for the design, synthesis and application of quinoxoline based organic dyes with multiple anchoring groups in practice and theory.