Preparation Of Diphenylpyrane And Their Performance In Organic Solar Cells

Dye-sensitized solar cells(DSSC)have attracted much attention in recent years because of their simple preparation,large-scale production and high photoelectric conversion efficiency.The classic sensitizer with high photoelectric conversion efficiency is mainly metal dyes,in which precious metals were used,with environmental complex pollution,In addition,the synthesis steps of metal complex dyes are complicated and difficult,and the low molar absorptivity limits their further application.However,metal-free organic dyes have a wide range of materials,low cost,simple synthesis and purification methods,adjustable structures,and high molar absorption coefficients,which have attracted widespread attention.At present,there are more studies on the donor and π bridge parts of metal-free organic dyes,but less on the acceptor part.Most of the molecular structure acceptor reported in the related literature of dye-sensitized solar cells are mainly anchored by a single cyanoacetic acid group in the para-position,and little research has been done on the substitution positions of anchor groups.Therefore,using diphenylpyranylidene material as the donor material and biphenyl as the π bridge,the effects of different structure moieties and anchoring positions on the photophysical and electrochemical properties of sensitizers and their electron injection and charge recombination processes in DSSC devices were studied.The structure of the sensitizer not only determines its light absorption performance,but also affects the electron injection into the titanium dioxide conduction band.the unreasonable molecular structure also causes a large degree of electron recombination.Therefore,it is an important way to optimize the performance of DSSC by adjusting the light absorption performance of sensitizer and controlling the electron transfer process in DSSC through the structure design of sensitizer.The first part of this thesis is firstly to designed and synthesized dye molecule W1 and W2.Extended π system dual-anchored dye molecule W2 with high molar absorptivity,which can compensate for the absorptivity of ruthenium-based N719 by photophysical measurements.Compared with the adsorption performance of the mono anchor dye molecule W1,W2 has better competitive adsorption performance.Therefore,it was co-sensitized with N719 to prepare DSSC devices.The current-voltage test(I-V)showed that the N719 and W2 co-sensitized system exhibited higher photocurrents due to their higher molar absorption coefficients and wider light absorption ranges,which makes the photocurrent conversion efficiency(PCE)of N719 from 7.77 % to 8.20%,and the photoelectric conversion efficiency of the system can be finally improved to 8.49% by adding a co-adsorbent.T To improve the optical absorption range of sensitizer,rhodamine-3-acetic acid group with strong electron-withdrawing properties was introduced into dye molecules as the acceptor parts to expand the optical absorption range of sensitizer WRh.The results show that WRh does widen the absorption range of the dye relative to W2,but due to the presence of a saturated methylene group in the rhodamine-3-acetic acid group,the conjugation performance of the entire molecule of WRh is blocked,and the PCE of W2 decreased from 4.77% to 0.65% of WRh.In the first part,it is found that cyanoacetic acid has better performance as anchoring group than rhodamine-3-acetic acid group.So,in the second part of this paper,sensitizers W-Ortho,W-Meta and W-Para were synthesized with the anchor groups in the ortho,meta and para positions.the structure of these sensitizers were calculated by density functional theory calculation(DFT)and characterization of UV absorption spectroscopy,cyclic voltammetry(CV)and differential pulse voltammetry(DPV)were captured as well.Finally the I-V,incident photon-to-current conversion efficiency(IPCE)and electrochemical impedance spectrogram(EIS)were also measured for the fabricated devices.It is shown that the presence of intramolecular hydrogen bonds in the abchored group of sensitizers can significantly improve the photoelectric conversion efficiency of DSSC devices.the sensitizers did not form intramolecular hydrogen bonds.the PCE of W-Para was 0.40%,and the PCE of W-Ortho and W-Meta were 0.24% and 0.18%,respectively.the higher PCE were obtained with better intramolecular charge transfer performance,better electron injection ability,larger composite resistance and longer electron lifetime.However,when intramolecular hydrogen bonding existed in the anchoring group of the ortho-anchor sensitizer W-Ortho,the hydrogen-oxygen bonding effect on the carboxyl group of the anchoring group was weakened due to the hydrogen bonding effect.Furthermore,the coupling between the anchoring group and the titanium dioxide film was promoted,the electron injection was enhanced,and the composite resistance was increased.In the end,W-Ortho achieved a high PCE of 0.73%.