The Influence Of Hole Injection And Transport On The Performance Of Organic Optoelectronic Devices

The development of the organic materials and the thin-film optoelectronic devices promotes the progress of the organic optoelectronic field in the recent twenty years.Organic materials possess many superiorities over the inorganic materials,including the diverse fabricating process,wide resources of the materials,and the compatibility with the large-area fabricating process.Therefore,the organic material-based thin-film optoelectronic devices have promising applications in the fields of the flat panel display,radio frequency identification,ultra-violet detection,gas sensor,and electronic paper.The thin film optoelectronic devices mainly include three types,which are organic light-emitting device?OLED?,organic thin film transistor?OTFT?,and organic solar cell?OSC?.Based on the working mechanism of the OSC,the organic photodetector?OPD?can be fabricated to detect the light ranging from ultra-violet to ultra-red.Till now,the research on these three types of devices has obtained great progress.Among them,the injection and the transport of the charge carrier plays an important role in the device performance.Superior injection and transport of the charge carrier ensure the high performance of the organic electronic devices.Hence,to improve the device performance,better understand the working mechanism,and optimize the device structure,it is necessary to investigate the charge injection and the transport in the optoelectronic devices.Based on these three kinds of optoelectronic devices,this study focuses on optimizing the performance of the devices through selecting different kinds of hole transporting layers?HTL?.Four aspects are included:1.Stable white OLED devices based on different HTLs was studied.Highly color stable pure white OLEDs with a non-doped blue emitting layer?EML?was fabricated.The OLED adopting a 4-aryloxy-1,8-naphthalimide derivative FluONI combined with orange emitting exciplex at the interface of electron donor/FluONI.To modulate the exciplex emission band and the hole injection barrier,three kinds of hole transport materials consisting of amino groups with stepped highest occupied molecular orbital?HOMO?levels were introduced as electron donors.Pure white emission with a standard Commission Internationale de 1'Eclairage?CIE?coordinate of?0.33,0.33?was achieved by adopting N,N?-diphenyl-N,N?-bis?1-naphthyl?-1,1?-biphenyl-4,4?-diamine?NPB?as HTL with a relatively deep HOMO level and an optimized 30 nm-thick EML.Meanwhile,excellent color stability was also obtained.A slight CIE coordinates shift of?0.01,0.01?at a luminance range from 100 cd/m² to 4000 cd/m² was observed.According to the systematic analyses of the electroluminescence spectra,the pure white emission benefited from the broad emission bands of both FluONI and exciplex.Meanwhile,the pure white emission with high color stability at different drive voltages were attributed to the sustainable equilibrium between FluONI intrinsic emission and exciplex emission.2.The effect of the hole transporting material on the performance of pentacene based OTFT was investigated.Three kinds of hole transporting materials of subphthalocyanine chloride?SubPc?,triphenyldiamine derivative?TPD?,and 4,4?,4??-tris[3-methylphenyl?phenyl?amino]triphenylamine?m-MTDATA?were adopted as the hole transporting buffer layer.The effect of the buffer layer on the saturation current,the field-effect mobility,the on/off current ratio,and the threshold voltage were systematically studied.Meanwhile,the film thicknesses of these three kinds of buffer layers were optimized.The optimized thicknesses of SubPc,TPD and m-MTDATA were 3 nm,2 nm,and 2 nm,respectively.Moreover,it was found that OTFT with m-MTDATA hole injection layer exhibited the best performance of the charge carrier mobility at 0.67 cm²/Vs compared to other two kinds of materials.3.The effect of differenc HTL on the performance of the OSCs was studied.The effect of different organic hole injection meterials as HTL on the performance of the OSCs was studied.Five small-molecular materials working as HTL in poly?3-hexylthiophene??P3HT?:PCBM bulk heterojuncion based organic polymeric OSCs were studied:NPB,MoO3,4,4?,4??-tris?carbazol-9-yl?triphenylamine?TCTA?,4,4?-cyclohexylidenebis[N,N-bis?p-tolyl?aniline]?TAPC?,and m-MTDATA.When adopting NPB as the HTL,the performanc of the OSC was optimized to the maximum performance.Our results indicated that NPB could not only improve the hole mobility of the device,but also form a good ohmic contact between the active layer and the anode.Meanwhile,when NPB was evaporated on top of MoO₃,the performance of the OSC was further improved to 2.96%.This was because the energy of HTL was optimized and the oxygen defect on the surface of the MoO₃ was decreased.4.The effect of the double anode-buffer layer on the performance of the organic integrated device with ultra-violet photodetective and electroluminescent properties was analyzed.The effect of the poly?3,4-ethylenedioxythiophene?polystyrene sulfonate?PEDOT:PSS?and MoO₃ double anode-buffer layer on the CzPhONI based organic integrated device with ultra-violet photodetective and electroluminescent properties was studied.This integrated device was ultra-violet photodetective under reverse bias while exhibited electroluminescent properties under forward bias.When the double anode-buffer layer was introduced,for the light-detection model,the hole transfer between the anode and the active layer was enhanced,the detectivity was 5.4×10¹⁰ Jones under-2 V,which was 4.2 times higher than that of the control device.On the other hand,for the light-emitting model the band gap between the anode and the active layer was also modified with the introducc of the double anode-buffer layer,the optimized hole injection resulted the maximum brightness of 1107 cd/m²,which was 1.6 times higher than that of the control device.In summary,this thesis systematically studied the effect of the charge injection and the charge transport on the organic optoelectronic devices,paving a way to the mechanism study and the application of the HTL.