Application Of ZnO/Mg:Ag/ZnO Transparent Composite Cathode In OLED

Organic light-emitting diode(OLED)has been widely used in various consumer electronic products.Their high contrast ratio,wide color gamut,large viewing angle,low energy consumption and fast response speed make them quickly seizing the traditional liquid crystal display(LCD)market.As one of the important research branches in the display field,top-emission and transparent OLEDs have always been an important research direction for researchers.To obtain more competitive light sources and displays,further improving OLED performance is still a challenge.As the intermediate layer of the OLED device,the organic functional layer has poor resistance to high radiation,solution and high temperature,so it has high requirements on the preparation process of the top cathode.When light escapes through the transparent cathode on the top of the device,the structure and composition of the transparent cathode and its deposition technology play an important role in the final performance of the device.The traditional sputtering technology is not suitable for the preparation of the top cathode,so the non-destructive thin film preparation technology is very popular.Cathodes made of Mg:Ag alloys are particularly popular in the industry due to their good charge injection characteristics,especially in the field of top-emitting OLEDs.However,its low transmittance has become a pain point in the industry,and finding a suitable solution has always been the direction of the efforts of enterprises and scientific researchers in universities.In the work of this paper,based on the industry pain points mentioned above,the transparent composite cathode in the OLED has become the core of this work.At the same time,we explore the parameters and process conditions that may affect the performance of the electrode,and analyzed the physical mechanisms involved.Furthermore,the designed composite cathode was applied to both top-emitting OLED and transparent OLED,and compared with the one prepared with Mg:Ag alloy as the cathode.The previous work mainly focuses on the optical and electrical properties of the electrode,deep theoretical analysis is rare.In this paper,by introducing the metal-semiconductor contact theory and combining with the test results of the Hall effect,a design concept of using a contact degeneracy mechanism to achieve a high transmittance and conductivity composite electrode is proposed,which is verified in the research project experiment with the enterprise.In this work,we developed a highly transparent(86%in the visible light range)conductive laminated cathode using atomic layer deposition.ALD ZnO is presented with the intention of protecting a vulnerable ultrathin Mg:Ag alloy layer while preserving its low WF in the entire structure.In this research,the top-emitting OLED prepared based on the novel laminated cathode achieved a 85.8%increase in brightness,compared with the devices made with Mg:Ag cathodes,In addition,the total luminance of transparent OLEDs increase 34.4%when compared with the devices prepared with Mg:Ag cathode.And the average transmittance of the device still reaches about 77.2%,in the visible light range.