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Study On The Mechanism Of The Cathode And Anode Modification To Improve The Performances Of Polymer Light-emitting Diodes

Posted on:2018-01-19Degree:MasterType:Thesis
Country:ChinaCandidate:H S WuFull Text:PDF
GTID:2348330536979999Subject:Optical engineering
Abstract/Summary:PDF Full Text Request
Organic light-emitting devices(OLEDs),as a new generation of display technology,it not only overcomes the narrow perspective,low brightness,complex device process and other shortcomings,but also has the advantages of fast response,low energy consumption,all solid-state,ultrathin,self-luminous,wide operating range and the use of flexible substrates.According to the molecular weight of the luminescent material,OLEDs can be divided into two types: small molecular OLEDs(Sm-OLEDs)and polymer light-emitting devices(PLEDs).Compared with Sm-OLEDs,PLEDs have their unique advantages,such as simple preparation process,low cost and conducive to large area display development.However,despite the rapid development of PLEDs in recent years,the performance of the device such as efficiency,life,and stability,still need to be improved.That's to say the improvement on device configuration and material design still need to be developed and studied.Among the performances improving approaches,the modification of the electrode is a very effective way by improving the carrier injection,and therefore the charge balance inside the emissive layer.That is a simple,cheap and efficient method.It has been widely concerned and studied because of its advantages.Based on it,this article mainly improves the PLEDs performance via modifying the electrodes of PLEDs.Two approaches were used: the polar solvent treatment method and the electrode resistivity optimization method to enhance the carrier injection and charge balance of the PLEDs,thereby improving the efficiency of the device.The working mechanism is also studied.The specific research contents are divided into the following two parts:Part 1,the surface of the emissive layer P-PPV was modified with a polar solvent to improve the injection of electron,thereby improving the performance of PLEDs.Different from the alcoholic solvents such as methanol,ethanol or octafluoropentanol used in previous reports,we modified P-PPV with polar solvent DMF,which is non-alcoholic with large dipole moment.Experimental data show that compared to the untreated control device,methanol modification improved the current efficiency of the device by 17%,while the DMF modification increased the current efficiency of the device by 68%.Considering the higher boiling point of DMF,we mixed different volumes of DMF into methanol to modify the P-PPV surface,in order to control the residual of DMF.The experimental results show that the efficiency of mixed solvent modified device was improved greater than the methanol treatment.And with the increase of the doping volume of DMF in methanol from 5%,10%,20% and 40% to 60%,the luminous efficiency of device showed a parabolic variation,increased first and then reduced.When the doping ratio is 20%,the highest efficiency is achieved.The luminous efficiency of the PLEDs device is increased by up to 126% compared to the control device.It can be seen that a simple polar solvent treatment method can bring about a significant improvement in device performance.In order to study the reason for the considerable improvement of the luminous efficiency of PLEDs by solvent modification,the surface morphology and roughness,UV-visible absorption,surface potential and surface electron structure of P-PPV were examined.The enhancement of electron current density and open circuit voltage of PLED devices were verified.Part 2,PLEDs based on p-type Si(p-Si)anodes.Indium tin oxide(ITO)transparent conductive electrode was usually used for the anode of traditional PLEDs.However,the indium element in ITO is scarce in the earth.This problem will be exposed when ITO was widely used.The content of Si in the earth is 26%,which is only smaller than that of oxygen.Therefore,if Si was used as the anode,there will be no source material shortage problems.We fabricated high efficiency PLEDs based p-Si anode,and investigated the effect of the resistivity of p-Si anodes on the performance of PLED devices.The experimental results show that with the increase of p-Si resistivity,the current density of the device at the same voltage increases monotonically,and the luminous brightness and efficiency increase first and then decrease.When the p-Si resistivity is 0.1? · cm-3,the optimum power efficiency is obtained.
Keywords/Search Tags:Polymer light-emitting diodes(PLEDs), Electrode modification, Polar solvent, Charge balance
PDF Full Text Request
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