Development Of New Flexible Electrodes And Their Application In Organic Electronic Devices

Flexible organic optoelectronic devices such as flexible organic light-emitting diodes?FOLEDs?and flexible organic solar cells?FOSCs?have gained much attention in recent years due to their flexibility,large-area and low cost,etc.In particular,FOLEDs with excellent properties of light weight,shock-resistance,and portability are called“dream displays”.FOSCs can be used to solar sailing boats and solar backpacks,etc,which are the ideal power source for many mobile electronic devices.However,there are still many technical problems hinder the commercial application of flexible organic optoelectronic devices.And the development of new flexible electrodes is one of the key factors.This paper focuses on the fabrication of flexible electrodes and their applications in organic optoelectronic devices.We achieved the optimized surface morphology and performance for graphite electrodes by using surface modification with ultrathin Ag layer.On the obave basis,we employed PEDOT:PSS to modify Ag nanowires?Ag NWs?as the top electrode for FOSCs.In order to further improve the comprehensive performance of Ag NWs electrode,we prepared a mixed dimension composite electrode?MDCE?combaining Ag nanoparticles?Ag NPs?,Ag NWs and Graphene.The main research contents are summarized as follow:Firstly,the surface properties of the graphite electrode were optimized by evaporating an ultra-thin Ag film on the surface of graphite electrode.The optical and electrical properties of modified graphite electrode were thoroughly investigated by controlling the thickness of the Ag film.The result shows that the graphite electrode modified by 1 nm Ag layer has the best performance with the low surface resistance of3.82?sq^-1 and the high reflectivity of 57.9%,respectively,as well as the excellent flexibility.We fabricated highly efficient red,green and blue top-emitting FOLEDs based on the optimized graphite as a flexible bottom electrode.And the maximum current efficiencies of red,green and blue devices are 15.0 cd A^-1,50.2 cd A^-1 and 16.8cd A^-1,respectively.Secondly,the performance of FOSCs by using PEDOT:PSS modified Ag NWs as the top electrode is studied.Here,we applied the Ag film modified graphite electrode as the bottom electrode to fabricate the top-illuminated FOSCs with the PTB7-Th:PC₇₁BM as active layer.The maximum power conversion?PCE?efficiency of the device is about 5.31%.Furthermore,we obtained a transferable Ag NWs top electrode structure by spin-coating Ag NWs dispersion on PDMS film.The optimized all-solution processed FOSC device using PEDOT:PSS modified Ag NWs as top electrode achieve a high PCE of 3.76%.More importantly,the device based on Ag NWs top electrode has excellent stability and flexibility.The PCE can still be maintained 80%of the original efficiency after being placed in the air for 10 days.Thirdly,based on the above work,we prepared a transparent MDCE by combining silver nanoparticles Ag NPs and Graphene to further improve the optical and electrical properties of Ag NWs electrodes and to replace the traditional largely used transparent electrode ITO.Ag NPs can effectively fill the gaps of the Ag NWs network,increasing the contact for Ag NWs and realizing the light absorption enhancement for the active layer by suface plasmon resonance effect.Graphene can effectively modify the surface of Ag NWs and improve the mechanical stability and air stability of the entire electrode structure.The result shows that the PCE of FOSCs based on optimal MDCE electrode structure reached to 2.23%and the stability of the device has also been greatly improved.Through the above research work,we not only solved the problem of low flexibility and stability for traditional electrode,but also prepared various flexible organic optoelectronic devices,which provide technical support for developing high-performance flexible and large-area organic optoelectronics.This paper also provides a guideline for the developing flexible electronic skin and wearable smart devices and their practical application in the future.