Theoretical Study On The Photoelectric Properties Of Aniline Dyes In Dye-sensitized Solar Cells

With the rapid development of today's society,mankind's demand for energy is also growing.However,the depletion of fossil energy is far from meeting the needs of the rapid development of society today.Meanwhile,it will also lead to increasingly serious environmental pollution and energy shortages.Developing renewable energy is one of the effective ways to solve the above problems.Solar energy has unique advantages in renewable energy: 1.No geographical restrictions,the sun can be directly collected and used;2.solar energy is one of the best clean energy;3.Dequate energy reserves,the energy of sun radiates to the earth is equivalent to 130 trillion tons of coal a year.Solar cells are the most direct and effective way to use solar energy.There are all varieties of solar cells,including silicon-based solar cells,perovskite solar cell(PSCs)and dye-sensitized solar cells(DSSCs),etc..A considerable interest has been paid to dye-sensitized solar cells(DSSCs)presenting excellent photovoltaic performances due to their simple manufacturing process,low cost and environmental friendly.Sensitizers as one of the core components of DSSCs,greatly affect the overall efficiency of batteries.Compared with metal dyes,organic dyes have the advantages of abundant raw materials,high molar absorbance,simple preparation process and flexible structure.However,the photoelectric conversion efficiency of the organic sensitizer battery is generally low,which seriously restricts its large-scale commercial production.Therefore,the search for high efficiency and cheap sensitizers has become the research focus of scientists.There are many kinds of organic dyes,how to pick out excellent sensitizers from various dyes is the most important thing in the process of scientific research.In response to this problem,related researchers have proposed: Research Model of "Theoretical Design-Experimental Development".First,the overall performance of the dye was evaluated by theoretical simulation,then decide whether to conduct experimental synthesis.This can reduce unnecessary experimental synthesis and reduce research and development costs.Meantime,the accuracy of theoretical simulation becomes important.Nowadays,there are countless theoretical studies on organic sensitizers,but most of them have the following problems:limited to analysis of molecular structure of dye,dye front-line molecular orbitals(FMO)and absorption spectra,however,ignoring the interfacial properties of dyes and semiconductor materials,unable to fully evaluate the performance of dyes.In response to the above issues,the static properties of the dye molecules with different structure types and the interface properties of the dye-titanium dioxide adsorptionmodel are studied in detail.The effects of rich/electron-deficient groups as bridges and co-receptors on the overall structure and performance were studied.Most importantly,the short-circuit current(JSC)and open-circuit voltage(VOC)and the photoelectric conversion efficiency(?)were quantitatively calculated using different methods.The specific research content is as follows:1,Four dye molecules 1,2,3 and 4 with different ?-bridge groups were studied using density functional theory(DFT)and first-principles.They employ triphenylamine(TAA)group as donor,phenothiazine as auxiliary donor,cyanoacrylic acid as acceptor,and azobenzene derivatives as ? groups,respectively.1 and 2 are experimentally synthesized dyes.Based on dye reported in the literature,4H-cyclopenta[2,1-b:3,4-b']dithiophen(CPDT)and 3,4-ethylenedioxythiophene(EDOT)groups were introduced in ? bridge to design 3 and 4.The frontier molecular orbitals and absorption spectra are investigated by B3LYP/6-31G(d,p)level of theory.The results showed that in addition to the maximum absorption wavelength of dyes 3 and 4,there was another strong absorption at 400-550 nm.Quantitatively calculated that JSC of 3 and 4 is higher than 1 and 2.In addition to,explored the interface properties of dye-Ti O2,considering the adsorption energy,density of states(DOS)and partial wave density(PDOS)of all dyes.The quantitative results show that dyes 3 and 4 have higher open circuit voltage(VOC).In combination with 3 and 4 with larger JSC,we predict that the 3 and 4 will receive higher photoelectric conversion efficiency(?).Finally,considering the aggregation effect of molecules,a 10 ps dynamics simulations are performed for the dimer-Ti O2 adsorbed system.The average electron coupling of 3 is lowest,indicating the less aggregation effect.Therefore,it was proved that by introducing an electron-rich group combined with azobenzene as a ? bridge,JSC and VOC can be increased at the same time,which is conducive to improving the overall efficiency of the battery.2,According to experiment reported of a D-?-A-A type organic dye based on anthracene,we strategically designed a series of anthracene-based organic dyes 1-4 by introducing different ?-bridge or auxiliary acceptor groups.Their geometric configuration,frontier molecular orbitals,absorption spectra,and aromaticity were explored by the first-principles calculations.It is found that the introduction of electron-rich thieno[3,2-b]thiophene-based ?-spacer in dye 2 induces the blue-shifting of maximum absorption band with respect to dye 1,while the inclusion of electron-deficient diketopyrrolopyrrole-based?-bridge in dye 3 and thieno[3,4-b]pyrazine-based auxiliary acceptor in dye 4 can remarkably extend the optical absorption into the 550-650 nm region.From the aromatic analysis of dyes,it is plausible that dyes3 and 4 may have better characteristics of electron delocalization and electron transfer.The dye-semiconductor adsorption system was studied,and the results showed that the adsorption of 3 and 4was more stable and had shorter electron injection time.The short-circuit photocurrent density(JSC),open-circuit voltage(VOC),fill factor(FF),and the corresponding photoelectric conversion efficiency(?)have been estimated by the normal model(NM)and improved normal model(INM).INM model can reproduce the PCE of experimental molecule TY6 very well,which proves the accuracy of our calculation.We predict ? values of dyes 3 and 4 will exceed 32%,which can be considered as potential organic materials in DSSCs devices.3,Based on the experimental synthesis dye of D-A-?-A,DH-16,building a simple model compound1,which by using the ethyl substituted triphenylamine group as electron donor,benzothiadiazole(BTZ)as an auxiliary accepto,carbazole(CZ)as the bridge,cyanoacrylic acid as the electron acceptor/anchor group.Then,three new dye molecules were designed on the basis of three different strategies: Altering the positions of BTZ auxiliary acceptor and CZ-based ?-bridge in dye 1 obtained dye 2;Replacing the BTZ auxiliary acceptor in dye 1 with 2-ethyl-2H-naphtho[2,3-d][1,2,3]triazole(ENT)group resulted in dye 3;Substituting the CZ-based ?-bridge in dye 1 with thieno[3,2-b]thiophene(TT)group got dye 4.In this chapter,the geometrical configuration,electronic structure,and light absorption properties of all isolated dye molecules are carefully studied using density functional theory(DFT)and first-principles.The interface properties of the dye@Ti O2 adsorption system are also discussed.At the same time,the photoelectric conversion efficiency(PCE)of dyes is predicted by using the INM calculation model mentioned in the previous chapter.It is found that the resulting dye by switching the position of auxiliary acceptor and ?-bridge exhibits an increased power conversion efficiency of 12.94%,in comparison to7.42% observed in 1.The effect of changing the co-receptor on the photovoltaic performance is very small,slight increase in efficiency of dye 3.The dye featuring the thieno[3,2-b]thiophene ?-bridge shows a broad absorption at the near-infrared region,leading to the best photovoltaic performance of 16.49%.Therefore,changing ?-bridge group may be the best strategy for enhancing the photovoltaic performance of such D-A-?-A dye systems.