Investigation Of Intermolecular Distance Dependence On Rubrene Molecular Singlet Exciton Fission

In recent years,more and more researchers start to study the singlet exciton fission process in our country and abroad,that referred to as exciton fission,exciton fission has attracted a broad interest in organic electronics.At present,the study of exciton fission mainly on the organic photovoltaic devices.The organic materials which can produce exciton fission,has be used as a new type of sensitizer,it can improve the photoelectric conversion efficiency apparent of the photovoltaic devices.the organic material which can happen exciton fission process,which absorbs a photon can be excited,and then a high energy singlet state exciton interacts with the molecule in the ground state,the singlet state exciton convert to a pair of low energy triplet state exciton,which will improve the photoelectric conversion efficiency of organic photovoltaic devices.Further the exciton of triplet state has longer lifetime than the singlet state exciton,hence the T1 state exciton diffusion range more wide,which is favorable for dissociate of the exciton,which can further improve the photoelectric conversion efficiency.At present,there are many scientific experiments that show the quantum conversion efficiency has been more than 100% in the organic thin film device.If the organic thin film material that have exciton fission process can be used in the industry,the energy problem will be solved.However,there are still many problems on singlet exciton fission process will be solved,and the researchers for the singlet exciton fission study technology is not mature.In this thesis,we will solve the following three problems.First,the question on fitting transient decay curve of the organic thin film materials.On the study of exciton fission process,the researchers mainly study the transient decay process of the organic material.There are two methods for fitting the transient decay curve: the one is a rate equation group coupling,the fitting curve agrees bad with the experimental curve.The other is a equation.Although the fitting curve agrees well with the experimental curve,but the physical meaning on the equation seems more like a mystery,our experimental group study the film transient decay process through different doping concentration of rubrene,to solve above problem.Second,the relationship between exciton fission rate and adjacent intermolecular distance of organic thin films with different doping concentrations.We study the films with different rubrene doping concentrations.Due to the different rubrene doping concentration will be lead to different intermolecular distance between adjacent rubrene molecular.Through study transient decay process of the films,we can obtain the rate of exciton fission,and then analysis of the relationship between the fission rate and the intermolecular distance.Third,about the physical mechanism of the exciton fission process.At present,there are two different views for the singlet exciton fission mechanism.One view believe that is "internal conversion" model;the other that is "double electron transfer" model.In this thesis,the singlet exciton fission mechanism is verified by the analysis of the exciton fission process.In the experiment,different concentrations of rubrene molecules were doped into the host material by two evaporative sources are vaporized method to made into organic thin film devices.Due to the different doping concentration of rubrene molecules can change the average intermolecular distance between adjacent rubrene molecular,the singlet exciton fission process is analyzed by the decay curves steady and photoluminescence spectra of the thin film devices measured at the steady state.In this dissertation mainly solves the above three problems.The main contents of each chapter are as follows:(1)The first chapter mainly introduces the kinetic process of singlet exciton fission,and that can produce several common materials of singlet exciton fission process can be occurred.At the same time,it explains the different viewpoints about the mechanism of singlet exciton fission.That also elaborates the research background about singlet exciton fission at nowadays,the problems and the development prospect of exciton fission at the present stage.(2)The second chapter,which mainly introduces that the preparation of the organic thin film device,and the measurement of the photoluminescence spectrum of the organic thin film device as well as the transient attenuation curve have been measurement.When we coating of the substrate,we usually use molecular beam epitaxy technology,the sample were evaporated should be under the conditions of the vacuum is about 10-5Pa.The chapter describes how should been use of the vacuum system as well as describes the monitoring system principles and operations in detail.At the same time,the photoluminescence spectra and transient decay curve of the organic thin film device made a brief introduction.(3)In the third chapter,the experiment measurements the photoluminescence and transient decay process of Alq3: rubrene(x%)organic thin films.We analyzed the results of the photoluminescence spectra show that the organic thin films emit light from the rubrene molecules.That also analysis of a set of rate equations that not only make the fitting curve can be agree well with the experimental curve,but also the group of rate equations with clear physical meaning.we also analysis the transient decay curves of the films has been doped with different concentrations rubrene molecular.The result shows that the relationship between singlet exciton fission rate and rubrene intermolecular distance is exponential descent.At the same time,the electron transition transfer process of singlet exciton fission process has been analyzed by the fitted transient decay curve,that results of the analysis show the mechanism of exciton fission is the "double electron transfer" model was identified.That will be helpful for analyzing the dynamics of the singlet exciton fission.