π-conjugated Organic Semiconductor Materials Ultrafast Kinetic Research

Organic optoelectronic materials are usually organic molecules withπ-conjugated structure and carbon atoms,which have photoelectric conversion characteristics and are widely used in organic transistors,organic light-emitting diodes,organic solar cells etc.Organic materials have many excellent characteristics,such as simple processing,low production cost,convenient structure and performance for material design,good film-forming and flexibility.In the research field of optoelectronic materials,due to the advantages of environmental protection,portability,flexibility and easy large-scale production,more and more researchers pay attention to organic optoelectronic materials and have great application prospects.The design and application of high-performance organic optoelectronic materials have always been the focus of research.In the organicπ-conjugated system,benzenes are the focus of research because of their unique photoelectric effect,including many excellent materials.For example,the singlet splitting material system can greatly improve the photoelectric conversion efficiency through the exciton splitting effect,which provides a promising research basis for the application of high-efficiency organic solar cells.Some of them have high blue fluorescence efficiency and have great potential in optoelectronic flexible devices.However,the understanding of the intrinsic properties of organicπ-conjugated organic materials,especially the photo generated carrier dynamics,is still not comprehensive,and the understanding of the basic mechanism is still not clear until now,which is a great obstacle to the further research and application of this kind of materials.So,we study the intrinsic characteristics ofπ-conjugated organic materials from the perspective of ultrafast carrier dynamics,and regulate the photogenerated carrier dynamics by adjusting the film morphology and preparation process.In this thesis,the photo generated carrier dynamics of TIPS-pentacene（6,13-bis（triisopropylsilylethynyl）pentacene）thin films was studied.The mechanism of singlet fission in TIPS-pentacene was studied by femtosecond transient absorption spectroscopy,and the existence of long-lived triplet pairs was confirmed.Then,by means of solvent annealing（SVA）and variable temperature testing,the relative relationship between triplet and triplet pairs of singlets splitting in tips pentacene was studied.The results are as follows（1）The intrinsic ultrafast dynamics of tips pentacene films excited by broadband light was investigated by using transient absorption spectroscopy with sub-10 femtosecond time resolution.By studying the transient absorption spectra in the near infrared band,the existence of long-lived"triplet pair"is confirmed.It is further confirmed that only part of the"triplet pair"will be decomposed into free triplet in the process of singlet splitting,which lays a foundation for the subsequent study of singlet splitting mechanism.（2）The steady absorption spectra,ultrafast spectra and carrier dynamics during the singlet splitting of tips pentacene thin films annealed in different solvents and at different temperatures were studied by solvent annealing and variable temperature measurement.The experimental results show that the longer the solvent annealing time is,the shorter the lifetime of the triplet T₁ and triplet to ¹（TT）,and the triplet to ¹（TT）is more sensitive to this change.In the absorption spectrum,the intensity of the absorption peak at 700 nm increases gradually,and the crystal form is better than that of the untreated film.As the temperature decreases,the relaxation lifetimes of T1 and ¹（TT）decrease,and the formation time of T₁ increases.It is speculated that these changes are due to the strong stacking interaction between neighboring molecules caused by lattice contraction.This research provides a new way to control the singlet splitting process by changing the morphology of the films.