| Organic light-emitting diodes(OLEDs)are widely used in display and lighting industry due to their fast response,light weight,thin thickness and low power consumption.Although OLED luminous materials have achieved the theoretical internal quantum efficiency of 100%,light extraction efficiency is still a concern due to total reflection and optical waveguide effects,which prevent all the light produced by the luminous layer from being emitted.Optical microcavity is an effective light extraction technology,but it still faces many problems such as short circuit and incompatibility of production process.To this end,this study aims to further improve the device efficiency by optimizing the OLED microcavity effect.Firstly,we propose a novel device structure for traditional bottom-emitting OLED that incorporates an "external microcavity" by depositing translucent Ag as a metal cathode,followed by organic layer(NPB)and metal reflection layer(Al)in turn.The"external microcavity" does not affect the carrier transmission of the device,but its interference effect enhances light output efficiency.In the light-emitting device with Irppy2(acac)as the guest material,adopting the "external microcavity" structure increases current efficiency from 52.3 cd/A to 59.1 cd/A.Considering the optical loss due to metal surface plasma oscillation(SPP),we add a high dielectric constant material MoO3 between the translucent Ag and the NPB,further increasing current efficiency to 65 cd/A.By analyzing how the device’s spectrum changes with angle,we can determine that the luminescence of the "external microcavity" device deviates from the expected Lambertian distribution and exhibits a high intensity in the small angle emission range,demonstrating the gain effect of light convergence.The results show that the optimized bottom emission device has good device efficiency with "external microcavity ",and thus provides a device structure to increase the efficiency of light extraction.Secondly,to address the incompatibility issue between reflection anode and production process,we designed a new composite anode composed of Cr/Al/Cr,covered with an ultra-thin titanium nitride(TiN)layer as a protective layer.The resistance of anode to air and alkaline environment is improved.With the green light-emitting devices using Irppy2(acac)guest material and Mg:Ag transparent cathode,the top emission device(TEOLED)achieves a maximum current efficiency of 71.2 cd/A and a maximum power efficiency of 66.7 lm/W with the TiN coated anode,which are 81%and 90%higher than the reference devices,respectively.The Cr/Al/Cr/TiN composite anode used as the bottom anode optimizes the microcavity structure,and TE-OLED realizes high efficiency of light production,demonstrating its potential for industrial applications.Thirdly,we solve the short-circuit problem by designing an ITO/Ag/ITO multilayer structure,utilizing the protective effect of ITO to avoid silver layer discontinuity or whisker formation.With Irppy2(acac)guest material in green devices,TE-OLED achieves 134 cd/A current efficiency and 32.4%external quantum efficiency using the multilayer structure as the total reflection anode,which is 135%and 110%higher than the reference device,respectively.By reducing Ag thickness in the ITO/Ag/ITO multilayer structure,a stable semi-transparent electrode is obtained for bottom emission microcavity devices,achieving 2 times current density gain and 1.25 times external quantum efficiency gain.The results show that ITO/Ag/ITO multilayer structure can realize efficient light production of microcavity devices,and the use of flexible,has great application value.Overall,based on optical theory and material application,this study improves device performance and reduces production cost by optimizing microcavity effect,which provides a new basis and method for further study of high-performance OLED. |
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