Design And Synthesis Of Novel Diphenylpyranylidene Materials And Their Application In Organic Solar Cells

Development and utilization of new energy sources is an urgent problem in the world today,of which solar energy is the most active area.Among them,dye-sensitized solar cells（DSC）have attracted much attention in the field of new energy materials due to their advantages of low-cost,colourful transparency and high photoelectric conversion efficiency.How to further improve the conversion efficiency and stability of DSC cell is the key to the industrialization of dye-sensitized solar cells.In the design of dye molecules,researchers have made a lot of efforts in the diversification of electron donating part,π-conjugation bridge and electron acceptor/anchoring groups,but relatively few results on improve the photoconversion efficiency（PCE）of devices by changing the electron acceptor/adsorption functional groups.At present,some researchers have done a series of related reports on how to introduce multi-carboxyl groups into organic dye molecules for further improving the photoelectric conversion efficiency.Organic thin-film solar cells（OSC）,another kind of organic solar cells,are also favored by scientists because of their low-cost,short energy recovery period,light weight,flexible devices and large area processing.In order to achieve the goal of commercialization,more innovations and explorations are needed in the design and synthesis of new materials for donors and acceptors of OSC,as well as in the development of new device structures,so as to achieve higher efficiency.In order to improve photocurrent conversion efficiency（PCE）of solar cells,two organic dyes and two small molecule donor materials were designed and synthesized from diphenylpyranylidene（DPP）,and their photophysical and electrochemical properties were studied.In the first part,the DPP group was used as electron donor,two new dye sensitizers D1 and D2 containing mono/di-anchoring groups was designed.The theoretical calculation was carried out at the 6-31G（d）level by using the B3LYP program of density functional theory（DFT）.The calculated energy levels of highest occupied molecular orbital（HOMO）and lowest unoccupied molecular orbital（LUMO）are discussed.The sensitizers were synthesized by three-step method,and their UV-Vis absorption spectra in DMF and on TiO₂films and redox potential were measured.The results indicated that dye molecule D2 with di-anchoring groups has a smaller tendency of aggregation than dye D1 with mono-anchoring group.The energy levels of dye D1 and D2are well-matched with those of the TiO₂ conduction band and I^-/I₃^-in electrolyte solution.The dye loading amount of dye molecules on TiO₂electrode was estimated by measuring the absorbance of dye desorption solution.The results showed that the geometrical configuration of dye molecules in DSC could affect the dye loading amount of dyes.And then,the synthesized dye sensitizers were applied to DSC and assembled into devices.Current-voltage（I-V）at 100 mW cm^–22 under simulated AM 1.5 G solar light condition,incidentphoton-to-currentconversionefficiency（IPCE）,electrochemical impedance spectroscopy（EIS）were measured.The results showed that the PCE of D1 sensitizer is 3.91%and that of D2 sensitizer is5.18%when N719 is used as standard dye and the PCE of DSC device is8.66%.In the second part,new small molecular donor materials DP1 and DP2,were designed by DFT calculation.And then synthesized.The UV-visible absorption spectra and redox potential were measured.Atomic force microscopy（AFM）was used to test the films of these two molecules,and the film formation was observed.The organic thin-film solar cell devices are fabricated by matching the energy level and complementary absorption range of the materials with small molecules.The results show that the efficiency of ternary OSC devices is always lower than that of binary standard devices due to the low solubility and low film-forming properties of DP1.In order to develop it into a novel organic small molecular material with excellent performance,further structural optimization and modification should be carried out.