Theoretical Studies On The Molecular Of Organic Photosensitizer For Dye-Sensitized Solar Cells

Since dye sensitized solar cells (DSSCs) were invented twenty years ago, researchers have always sought a good photosensitizer for DSSC. in order to improve the electro-optical properties of DSSC and enhance electro-optical energy conversion efficiency. To reduce the cost of DSSC. researchers have begun to pay close attention to the use of non-metallic organic photosensitizer dye as replacement of precious metal complexes in recent years. In this stage, researchers have recognized that the non-metallic organic photosensitizer molecules suitable for efficient DSSC should have the molecular structure of "electron donor-conjugated bridges-electron acceptor (D-Ï€-A)".At present, many kinds of D-Ï€-A non-metallic organic photosensitizer have been synthesized and have been used for sensitized DSSC, in order to gradually enhance the electro-optical energy conversion efficiency of DSSC. However, the electro-optical energy conversion efficiency of DSSC is still less than 10% now, which falls behind large-scale industrial production. There are several facets to this question:on the one hand the adsorption spectra of dye molecules at the short-wave area of ultra-violet visible spectra fail to make full use of solar energy; on the other hand the charge transfer efficiency from the excited state of dye to TiO2 electrode is low. The synthesis of organic dye photosensitizer with significant red-shift adsorption spectra is the urgent task of current research on DSSC.Due to the diversity of organic molecular structure, the photo-physical and electro-chemical characteristics of molecules may be adjusted to be suitable for DSSC through molecular modification. It will be a very economic and fast method to design new molecules by theoretically modifying molecules and predicting their properties before trying to synthesizing dye molecules. By DFT/TDDFT simulation calculation for currently synthesized dye molecules and comparison with experimental results, this paper sought the key indicators of the photosensitizer molecules that influence on the electro-optical properties and electro-optical energy conversion efficiency of DSSC; based on these indicators, the currently synthesized two kinds of dye molecules were modified, in order to select the organic molecules with good properties for DSSC, which provides reference for the further synthesis of efficient non-metallic organic dye molecules.By DFT/TDDFT simulation calculation for dihydroindole, polyene and furan dye molecules and comparison with experimental results, one found that the HOMO and LUMO energy levels of dye molecules, adsorption spectrum and molar absorption coefficient should be the key factors that determine the properties of DSSC.The DFT/TDDFT calculation for the increasement of conjugated bridges (methylidyne chain, thiophene ring and furan ring) show that the increase in conjugated bridges can cause the red-shift of molecular adsorption spectrum indeed. However, the calculation results also show that the conjugated bridges should not be too long, i.e. one unit should be enough, and two units should not be exceeded.Through the introduction of different electron-donating groups (-OH,-NH2,-OCH3) and electron-accepting groups (-CF3,-F,-CN) into different parts on the skeleton of dye D5 molecules.54 kinds of D5 analogue molecules were designed. By DFT/TDDFT simulation calculation for geometric structure, adsorption spectrum and energy level structure of these molecules, two kinds of molecules superior to D5 molecules in properties were sieved out. In the same way, by molecular modification for furan-laden dye F1, another two kinds of molecules superior to dye F1 molecules in properties were sieved out. This provides theoretical reference for the further synthesis of efficient DSSC photosensitizer.