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The Influence Of Regulation Of Electron Transport And Injection On The Performance Of Organic Semiconductor Devices

Posted on:2022-09-18Degree:DoctorType:Dissertation
Country:ChinaCandidate:D ZhaoFull Text:PDF
GTID:1488306524471054Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Along with the advent of the era of internet,blockchain,artificial intelligence,and6G,organic semiconductor devices(OSD)are playing an important role for display,photodetector,and sensing technology due to its advantages of light weight,low power,flexible.So far,Organic semiconductor devices,including organic light-emitting diode(OLED),Organic Photodetector(OPD)and Organic Thin-Film transistor(OTFT),are always the research hotspot in past 20 years.It is well known that the mismatch of transport and injection capability between electron and hole has always been a bottleneck problem in OSD.This results in the imbalance of charge in the OSD,which restricts the improvement of the device.Because the device structure,working principle and parameters are different between diverse kinds of OSD.It is necessary to propose solutions to solve the electron transport and injection problems of OSDs by combining the material design and synthesis,device structure construction,interface modification engineering and carrier regulation.Therefore,this work focused on charge carrier regulation to improve the performance of OSDs by regulating the transport and injection of electrons.The regulation mechanism is revealed from the aspects of material energy level,light field distribution and microstructure,which have four parts:1.Influence of heterojunction electron transport layer on the performance of OLEDAn electron transport layer composed of Copper(?)phthalocyanine(CuPc)and fullerene(C60)was introduced into the OLED.By optimizing the thickness of C60/CuPc,the light extraction efficiency and electron transport efficiency of the device were improved.Comparing with the current efficiency and power efficiency of control group,the optimized device was increased by 52%and 84%,respectively.In addition,the effects of C60/CuPc,CuPc and CuPc/C60 transport layers on the performance of red OLED devices were compared.It was shown that the charge generation capacity of C60/CuPc heterojunction promoted the electron transfer and injection,thus reducing the device driving voltage and improving the performance of device.At the same time,we studied the improvement of performance of C60/CuPc electronic transport layer in the red,green and blue OLED.Because there is an enough overlapping area between the emission spectrum of red emitting layer and the absorption spectrum of CuPc,a promising charge generation capacity and electron transport and injection capacity of the electron transport layer can be obtained due to the energy band bending of C60/CuPc.2.Influence of electron injection regulation of the intermediate layer on the emission color stability of white OLEDA white OLED consisting of red and blue emission units was fabricated by using C60/CuPc heterojunction as the intermediate layer.Because the electron injection ability of C60 into blue emitting unit is weaker than hole injection of CuPc into red light emitting unit,a color tunable OLED with maximum current efficiency of 20.4 cd/A is prepared.And emission color can gradually change from red to white with increasing voltage.Moreover,by switching the positions of red and blue light-emitting units,a white light OLED with(0.31,0.27)color coordinate was fabricated.To understand the principle of how the electron transfer and injection change the emission color stability of OLED,a theory model has been built according to the difference of energy level,utilization of triplet excitons and optical simulation light extraction.It provides a new way for the preparation of two kinds of OLED devices:color-tunable and white color-stable.3.Influence of conjugated polymeric modification for electron transport layer on performance of organic photodetectorTo avoid traditional modification method will reduce the photocurrent while suppressing the dark current of OPD,we use conjugated polymer poly[(9,9-bis(30-(N,N-dimethylamion)propyl)2,7-fluorene)-alt-2,7-(9,9-dioctyl)fluorene](PFN)to modify zinc oxide(ZnO)as electron transport layer for inverted OPD with 1 cm2 active area.The dark current of the device is reduced by two orders of magnitude,while the photocurrent remains almost the same,thus increasing the photo detectivity by 10 times.The results of interface morphology and energy level characterization show that PFN can reduce leakage current.At the same time,due to the enhancement of electron injection by energy level modification,a better emitting performance can be obtained,the brightness increased by 4.5 times,which indicates that the polymer modified method for electron transport layer is also suitable for OPD-OLED dual-function devices.4.Influence of polymeric grain boundary plasticizer on electronic transport performance of flexible OTFTA novel n-type OTFT device with high electron mobility and flexibility was prepared by using an end-functionalized polymer material as grain boundary plasticizer to plasticize the grain boundaries of high crystallinity electron-deficient small molecule films.The surface morphology,element distribution and film crystallization of semiconductor materials were characterized by atomic force microscopy(AFM),transmission electron microscopy(TEM)and grazing incidence wide-angle X-ray scattering(GIWAXS).The effects of grain boundary plasticizer on electron transport performance of organic semiconductor were investigated.The results show that thanks to the anchoring effect of the end modification and energy level optimization,this new plasticizer is embedded in the grain boundary of small molecules during the crystallization process,which not only plays the role of stress release in the bending process,but also improves the electron transport at the grain boundary.The electron mobility of fabricated flexible OTFT is comparable to that of the traditional OTFT,and the mobility of this flexible OTFT still retains 70%of the initial performance under the bending radius of 4 mm and bending times of 500 times.It reflects the advantage of grain boundary plasticizer in improving electron transport capacity and bending resistance.In conclusion,we focus on the regulation of electron transport and injection in organic semiconductor devices.The effects of interface energy levels,surface morphology and optical properties of materials on the performance of organic semiconductor devices,such as OLED,OPD and OTFT,was studied.Meanwhile,by combining with the theoretical model,the regulation mechanism was expounded,and the high-performance devices were fabricated.This work has reference and guiding value for the fabrication of integrated,multi-functional and flexible organic semiconductor devices,also for the synthesis of new electron transport and injection materials.
Keywords/Search Tags:Organic semiconductor device, Electron transport, Electron injection, Organic light-emitting diodes, Organic photodetectors, Organic thin film transistors
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