Competition And Regulation Of Exciton Reaction Process In Organic Doped Devices

Organic light-emitting diodes' s application in the display field is considered a grand technological revolution,beacsuse of it's great advantages in large amounts of materials,low cost,fast response,ultra-thinness and flexibility.Therefore,a large number of scientists have invested in the research of OLEDs,in order to look at their luminescence mechanism,and thus can effectively improve their luminous efficiency.In fact,the reactions inside the organic light emitting diodes are extremely complicated and not easily detectable.It has been found that the spin-related process inside OLEDs have sensitive response to the external magnetic field,thus the organic magnetic effect can be used as an indirect detection method to study the relevant processes.Among them,the magneto-electroluminescence(MEL)and the magneto-conductance(MC)can be used as two kinds of detection tools,which are respectively used for detecting light-emitting related process,as well as detecting charge injection and transport related carrier characteristics.Now,The fingerprint characteristics of MEL and MC for partial exciton reactions have been summarized,such as the MEL curves of both the Triplet-Triplet Annihilation and the Singlet Fission that affect the device's luminescence are showing completely opposite characteristics,and the MC fingerprints of the reaction between the triplet excited states and the charges are particular.Conversely,The organic magnetic effect feature fingerprints that had been known can be used to study the types of exciton reactions inside new devices and to explore the influencing factors of each reaction.In this thesis,we can control each type of reaction and achieve a horizontal comparison of all types of reactions when there are many kinds of excitonic reactions existing simultaneously inside the device.We selected materials and designed device structures to allow multiple exciton reactions coexist.The organic magnetic effect curves,the current-voltage curves,and the electroluminescence spectrum are observed by changing the doping concentration,the temperature,or the injection current of the device.Then we can analyze the the multiple reaction process,achieve the factors that affect various reactions and effectively regulate the specific processes.This work deepens the evolution of various types of excitons and provides theoretical guidance for the effective design of devices with high luminous efficiency and low energy consumption.The main contents of this thesis concludes the following four parts:In the chapter 1,we fist briefly describes the development history of organic electronics,and then introduces the device structure of organic light-emitting diodes,illustrates the electroluminescent mechanism and common microscopic processes.Finally,briefly states the basic concepts of the organic magneto-conductance(MC)and the organic magneto-electroluminescence(MEL),expounds the magnetic effect characteristic curves of the microscopic processes in the OLEDs,and reveals the development direction of the magnetic effect.Chapter 2 introduces the experimental equipment that required for manufacturing and measuring OLEDs,as well as describes the method steps for fabricating and measuring the devices.The manufacturing includes cleaning the substrate,spin-coating PEDOT:PSS aqueous solution and vapor-depositing organic functional layers and metal electrode.The device measurement includes measuring optoelectronic performance and measuring magnetic effects.The third chapter mainly introduces the light-emitting related processes,we fabricated the rubrene-doped devices.Its structure is ITO/PEDOT: PSS/NPB(40 nm)/Rubrene:DBP(1%)(x nm)/Rubrene((95-x)nm)/Bphen(25 nm)/LiF(1 nm)/Al(120 nm),the x represented the devices' s doped concentration.we made another reference device,Its structure is ITO/PEDOT:PSS/NPB(40 nm)/Rubrene(85 nm)/Rubrene: DBP(1%)(10 nm)/Bphen(25 nm)/LiF(1 nm)/Al(120 nm).we analyzed the MEL curves to study the exciton reaction processes in the doping system and found that there have three types of excitons inside the device,such as Triplet-Triplet Annihilation(TTA),Singlet-Triplet Annihilation(STA)and Singlet Fission(STT).Further studies have shown that these three reactions is sensitivity to the devices' s temperature,injection current,Rubrene:DBP(1%)layer's position and Rubrene: DBP(1%)layer's thickness.Both STA and STT were endothermic reactions,while TTA was enhanced at low temperatures;the TTA process and STA process had a requirement in relatively large injection currents,while the STT process required only a small injection currents to complete;the STA and TTA processes would occur when the Rubrene:DBP(1%)layer was close enough to the Al electrode,or when the Ruberne:DBP(1%)layer was thick.This work compares several types of exciton reactions that affect device luminescence,provids a theoretical reference for improving the luminescence properties in OLEDs.The fourth chapter mainly introduces the current-related exciton reactions,we fabricated devices with the structure ITO/PEDOT:PSS/m-MTDATA(40 nm)/CBP: x%DCM(40 nm)/Bphen(40 nm)/LiF(1 nm)/Al(120 nm)and found that the scattering of triplet-charge interaction(TQI)leaded to positive MC,while the dissociation of TQI leaded to negative MC through combining two non-Lorentzain formulas to fit the device's MC curves.The scattering process reduces the carrier conduction velocity that causes a decrease in current,while the restriction of the magnetic field on the scattering reaction makes the current larger,which is positive MC.The dissociation process increases the number of carriers that causes a larger current,while the restriction of the magnetic field on the dissociation reaction makes the current decrease,namely negative MC.Furthermore,when two kinds of reactions coexist,it was found that the concentration of triplet excitons is the main factor affecting the scattering and dissociation.The scattering reaction of TQI is more reactive in the excitonic reaction when the concentrations of triplet excitons are large enough;Inversely,the dissociation reaction of TQI is more reactive when the concentrations of triplet excitons are low enough.This work compares two exciton reactions that affect the current of the device and deepens the microscopic mechanism of the interaction between the charges and the excited states in the organic optoelectronic devices,provids a new way for the effective regulation of organic magnetic conductance.