Study On The Dependence Of Singlet Exciton Fission Between On Temperature And Intermolecular

In recent years,the phenomenon of singlet exciton fission?SF or exciton fission?has attracted more and more attention in the fields of physics,chemistry and organic electronics.In the existing organic materials,polybenzenes and derivatives?for instance,pentacene,rubrene and tetracene?have such properties.Exciton fission is the process,through the absorption of photon to generate singlet exciton S₁ with a higher energy in organic materials,and its half of the energy will transfer to another unexcited S₀molecules.And then,singlet exciton S₁ and S₀ molecules through the fast adversion process,into two triplet exciton T₁ with low energy.Analysis of many theoretical research and experimental results,the organic photovoltaic equipment which prepared by the materials with fission features,by absorbing a photon can generate two excitons,if the two T1-state excitons can disintegrate into the hole-electron pair,result in the the exponential growth of the number of current carriers,which can greatly improve the energy conversion efficiency of photovoltaic devices.Therefore,serving such material with the properties of exciton fission as a new type of sensitizer,it can be used to improve the conversion efficiency of organic photovoltaic equipment's energy.Moreover,the lifetime of the T₁-state is longer than the S₁-state,which will be more beneficial to the separation and dissociation of the exciton.However,this new technology can't be widely apply because of the uncertainty of many factors.Therefore,the key point of this thesis is to study the dependence on these factors in the process of exciton fission.This thesis selects rubrene molecule as the object material,and the inert molecules that do not fission as the main material,and by the means of inert molecules'adulteration,to prepare the BCP:rubrene?x%?,TPBi:rubrene?x%?,NPB:rubrene?x%?organic hybrid films in different doping density,and it's like.What's more,measuring the fluorescence and fluorescence decay process under this sample.Regulating the temperature in the range of 100K-300K,experiments show that while E?S₁?<2E?T₁?,the rate of exciton fission process affected by the change of temperature;and at room temperature,compared with different doping density of doped materials,found that rubrene molecule in different doping density of fission affected by the change of molecular spacing.It is proved that the change of temperature and the different distance in molecules will have different effects on the exciton fission process.In order to study this problems,the contents of this thesis are setted as below:?1?Chapter one shows a detailed introduction to the kinetic process of the process of exciton fission and introduces the current progress in the background of the exciton fission.At the same moment,aiming at the existing experimental conclusions in our group,we found other factors that affect the physical mechanism of exciton fission on the micro level,and confirming the research topic and contents of the postgraduate period.The second chapter shows a detailed introduction of the preparation of techniques and methods,and the measurement of the samples.?2?In the third chapter,via the measurement of BCP:rubrene?x%?,TPBi:rubrene?x%?,NPB:rubrene?x%?organic hybrid films'fluorescence under different temperature spectroscopy and fluorescence decay curves,we get a qualitative conclusion that the rubrene molecule in the fission is a thermal excitation process.And its could be well fitted by using a set of coupled rate equations.Then the important rate constants involved in singlet exciton fission process were obtained by curve-fitting.Futhermore,according to the detailed balance condition of molecular reaction dynamics and Arrhenius laws,the experimentally determined energy different in endothermic reaction was consistent with its theoretical value.It shows that when the exciton fission process is a thermal excitation process,additional phonons are needed to make up the energy difference of the reaction during the fission process.?3?At the fourth chapter,via the measurement of NPB:rubrene?x%?organic hybrid films under different density of fluorescence and fluorescence decay curves.And its could be well fitted by using a set of coupled rate equations,Then it also can get this important rate constants by curve-fitting.And the relation between fission rate constant and molecular spacing.The experimental results shows that the rate constants take on exponential change with the distance between molecules.This law is very similar to the Dexter energy transfer process of the organic materials,comparing that of the physical image of two kinds of transfer process,resulting the similar function relationship.And in-depth research,founding that the two transfer process can be explained by double electron transfer model in the process,this process also known as the"super exchange model".