Synthesis And Application Of The Quinoxaline-based D-A-?-A Metal-free Organic Dyes For Dye-sensitized Solar Cells

In recent years,with the drastic reduction of traditional energy sources and the increasing environmental pollution,human beings have been seeking and developing new energy sources that are clean and efficient.The dye-sensitized solar cell?DSSC?is a new generation of solar cells.The green energy has become a hot spot in scientific research around the world due to its adjustable molecular structure design,simple process,low production cost,and high photoelectric conversion efficiency.Dye sensitizers,one of the most critical components in dye-sensitized solar cells,play a crucial role in light trapping and electron transport.In the past dozens of years,studies have shown that the introduction of an extra acceptor with an electron-withdrawing ability?D-A-?-A type structure?in a D-?-A type pure organic dye molecule is advantageous in broadening the UV-visible absorption spectrum.adjust the energy level,improve the photoelectric conversion efficiency.In this thesis,a series of novel pure organic dye molecules based on D-A-?-A were designed and synthesized,and successfully applied to the dye-sensitized solar cells.The relationship between dye molecular structure and properties was studied by evaluating the photoelectric properties of dyes.The specific research work is mainly divided into the following aspects:?1?A series of organic dyes with a D-A-?-A structure,containing dipentyldithieno[3,2-f:2',3'-h]quinoxaline?DPQ?unit as?-spacer,indolineas electron donor and cyanoacetic acid as electron acceptor were designed and synthesized.Dipentylquinoxaline and dipentylpyridopyrazine with electron-withdrawing ability were introduced into the dye molecule as additional acceptors.The dye molecules were characterized by ¹HNMR,¹³CNMR and HRMS.?2?UV-visible absorption spectrum,fluorescence emission spectrum,solid UV-visible absorption spectrum,open-circuit voltage,short-circuit current density,density functional theory calculations,dye adsorption amount,J-V curve and incident photon-to-current conversion efficiency were used to analyze the photophysics of the DSSCs.Photophysical properties,electrochemical properties,and photovoltaic properties.The results showed that IQT with 2,3-dipentylquinoxaline as an additional acceptor in the series of dyes obtained J_sc of 16.87 mA cm^-2 under standard global AM1.5G solar illumination conditions.The V_oc is 710 mV,the fill factor FF is 0.67,and the photoelectric conversion efficiency reaches a maximum test result of 7.98%,far higher than the photoelectric conversion efficiency of DQ5?7.12%?.The short circuit currents(J_sc)exhibited by the IT and IPT are 14.40 and 12.89 mA cm-2,respectively,and the open-circuit photovoltages(V_oc)are 0.70 and 0.65 V,respectively.The fill factor?FF?is 0.61 and 0.64,respectively.Conversion efficiency was 6.22%and5.32%,respectively.Compared with DQ5 inserted the BTD unit,IQT not only has different acceptor,but also introduces two alkyl chain structures on the additional acceptor,which can effectively increase the open circuit voltage,which can inhibit dye aggregation and electronic recombination,further improve the photoelectric conversion efficiency.When IPT was adsorbed on the TiO₂ film,the UV-visible absorption spectrum showed a wider absorption range due to the additional electron accepting ability of dipentylpyridopyrazine as an additional acceptor.Compared with IQT,it had 9 nm red shift.However,short-circuit current,open-circuit voltage and photoelectric conversion efficiency of IPT are very low,indicating that the electron-withdrawing ability of dipentylpyridopyrazine is too strong and“electron trap”is generated during the electron transport.Therefore,when the electron-withdrawing ability of the selected auxiliary acceptor is too strong,it may form an“electron-trap”and then restrain the electron transfer process.Thus,a moderate electron-withdrawing unit as an auxiliary acceptor inserted into the?-spacer of dye is a promising way to improve photovoltaic performance.