Theoretical Study On Intramolecular/intermolecular Charge Transfer Of Organic Photovoltaic Heterojunction

Dyadmolecularorganicphotovoltaicheterojunctionscontaining donor/acceptor have received widespread attention in recent years,which not only have the basic characteristics of light absorption,exciton dissociation and charge transport,but also have simple battery fabrication process,low cost and stable D/A interface morphology.D/A monomolecular organic heterojunction active materials,in particular fullerenes as acceptors,are the most typical and widely studied mode ls.Because porphyrin has strong two-photon absorption,effective electron transfer and good thermal stability,and fullerenes have the advantages of suitable reduction potential and low recombination energy.In this paper,the method of density functional theory and time-dependent density functional calculation is used to calculate geometry structure,electronic structure and excited state properties of(F₁₅P)ZnP-C₆₀ dyad to further understand its excited state properties and intramolecular charge transfer.The geometry,electronic structure and excited state properties of a monomer and dimers which is DPP as a donor,and fullerene as acceptor were studied.The intramolecular/intermolecular charge transfer mechanism of dyad molecular organic photovoltaic heterojunctions containing donor/acceptor was described and analyzed in detail.The main work of this thesis includes:1.The geometry,electronic structures,and excitation properties of three meso-pentafluorophenyl substituented zinc porphyrin fullerene(F ₁₅P)ZnP-C₆₀ dyad were analyzed based on density functional theory?DFT?and time dependent DFT?TDDFT?calculations.The geometrical parameters provide the D-A distance is about 18.19?.The electronic structure analysis indicate s that the highest occupied molecular orbital and the lowest unoccupied molecular orbital are localized in porphyrin core and C₆₀,respectively.The transition configurations and the MOs suggest the excited states at the absorption maxima are local excited states,while the charge transfer?CT?states are transient intermediate.The population analysis supports the first singlet/triplet excited states are local excitations in porphyrin?LEP?.Quasi-degeneracy of excited states between LEP and local excitation in C ₆₀?LEC?enable the partial delocalization of eigenstates and excitation-energies over the D and A in dyad,while the quasi-degeneracy between CT and LEP generate synergistic enhancement effects for CT.The results of this work could be helpful to understand optoelectronic properties of(F₁₅P)ZnP-C₆₀ dyad.2.Based on experiments,the photoelectric conversion efficiency of the diathiafulvalene-functionalized diketopyrrolopyrrole–fullerene?DPP-Ful?as an active layer was 2.2%.In order to study intramolecular charge transfer,intermolecular charge transfer and the photoelectric properties of DPP-Ful dyad monomers and dimers.We constructed a monomer model and three dimer isomers.The geometry,electronic structures,and excitation properties of the DPP-Ful dyad monomer and three dimer isomers were analyzed based on density functional theory?DFT?and time dependent DFT?TDDFT?calculations.Electronic structure analysis shows that the highest occupied molecular orbital and the lowest unoccupied molecular orbital are localized i n DPP and fullerene,respectively,meanwhile the HOMO-LUMO gap?HLG?by?B97XD/6-31G?d,p?calculating is very small,which is beneficial electronic transition.The transition configurations and the MOs suggest the excited states at the absorption maxima ar e local excited states.For the constituent dimers,analyz ing their transition configuration and MOs find that both intramolecular charge transfer and intermolecular charge transfer during electron excitation,and there are also localized excitations in pa rt of the same fullerene.However,most of the excited states are charge transfer states.This work will help us to further understand intramolecular charge transfer and intermolecular charge transfer.Also,it can help us understand the photoelectric properties of DPP-Ful dyad monomers and dimers.The above works studied the geometry,electronic structure and excited state properties of organic photovoltaic heterojunctions containing donor/acceptor dyad molecules by quantum theory.In addition,we further explored the electronic process,charge transfer characteristics and better understood the charge transfer mechanism.And understanding the charge transfer process can help us analyze the influencing factors of photoelectric conversion efficiency,which provides a strong theoretical basis for the experiment.