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Computational Methods For Excited States Of Donor-acceptor Complexes And The Theoretical Study On Dye Sensitizers C276,C277 And C278

Posted on:2019-06-22Degree:MasterType:Thesis
Country:ChinaCandidate:P XuFull Text:PDF
GTID:2371330596953880Subject:Condensed matter physics
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In recent years,the photovoltaic cells?PVs?,which transform inexhaustible solar energy into electricity,is therefore one of the most promising long-term solutions for clean,renewable energy.Although there are solar cell devices based on inorganic semiconductor to efficiently harvest solar energy,the cost of these conventional devices is too high to limit large-scale commercial application.Organic solar cells and dye-sensitized solar cells have the advantages of low production cost and ecofriendly.The synthesis of heterojunction solar attracted people's attention due to their short diffusion length and large increase in donor-accepter interface area.The properties of materials of the active layer are the most d etermining factor in the overall performances of polymer solar cells.Dye sensitizers are an important part of dye-sensitized solar cells,its light harvesting and electron transfer process directly affect the stability and performance of the cells.Therefore,in this paper,we study the properties of the electron-excited state of the interface at the acceptor-heterojunctionand give a reliable method for describing the electronic excited state.The second part is an in-depth study of the relationship between the molecular structure of the organic photosensitizer and the optoelectronic properties.Theoretical study on the charge transfer properties of organic heterojunction solar cells has important research significance.We find a way to reliably describe the electronically excited state at the interface to the acceptor.And hope that our research can give researchers theoretical basis and guidance in designing receptor materials.In order to get the balanced description of different excitation types for electron donor-acceptor systems,including singlet charge transfer?CT?and local excitations,as well as triplet excited states,several ab initio and density functional theory?DFT?methods for excited states calculations were evaluated based upon the selected model system benzene-tetracyanoethylene?B-TCNE?complexes.On the basis of benchmark calculations of equation-of-motion coupled-cluster with single and double excitations,the arithmetic mean of the absolute errors and standard errors of electronic excitation energies for the different computational methods suggest the M11 functional in DFT is superior to the other tested DFT functionals,and time dependent DFT?TDDFT?with Tamm-Dancoff approximation improves the accuracy of the calculated excitation energies relative to full TDDFT.The performance of M11 functional underlines the importance of kinetic energy density,spin density gradient and range separation in the development of novel DFT functional.According to TDDFT results,the performance of different TDDFT methods in CT properties of B-TCNE complexes were also analyzed.In dye-sensitized solar cells,sensitizers play a key role in absorbing photons and generating and transporting electrons.The dye sensitizer plays a very important role in generating the photo-induced electrons and injecting them into the conduction band of the Oxide semiconductor directly affect the performance of the cells.In this article,three dyes C276,C277,C278 were the most efficient metal-free donor/acceptor dye up to now,to screen out outstanding dyes for organic dye-sensitized solar cell?DSSC?.All three dyes are benzothiadiazoles benzoic acid as electron acceptors with different electron donors.Based on the analysis of th results,we know that the introduction of cyclanes in C277 and C278 can reduce the HOMO-LUMO gap and improve the intramolecular charge transfer process.An effective intramolecular charge transfer excitation occurs in C276,C277,and C278,and the electrons are efficiently transferred to the electron acceptor.The result of the absorption spectra show that after binding to the semiconductor,the absorption spectra of three dyes-TiO2 complexes are all red-shifted significantly as compared to that of the isolated dyes.Our study reveals the possibility of a favorable C276?C277?C278 dyes of electron transfer that the electron injection from the excited dyes to the nanoparticle TiO2 Cluster conduction band?CB?.Our work has verified the introduction of perylene and cyclopentane in C277 and C278,compare with C276,the energy gap of HOMO-LUMO is smaller,and the LUMO energy level is close to the conduction band of TiO2.At the same time,the oscillator strength corresponding to the maximum absorption peak is larger,which means thatis larger.The importance of this cyclanes for improving the conjugation degree of organic dye-sensitized solar cells was verified,and the photoelectric conversion property of the organic dye-sensitized solar cell is improved.
Keywords/Search Tags:Donor-accept complexes, TDDFT, Excited states, Charge transfer, Organic dyes, Electron injection
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