Transfer Of Graphene Films Oriented To Flexible Transparent Electrodes With Uniform Resistance

Transparent electrodes with high transparency,conductivity and uniformity are very important for touch screens,displays,solar cell,light emitting diode and other devices.Graphene is recognized as an ideal material to replace the traditional transparent electrode material indium tin oxide(ITO).At present,there are many mechanical defects and cracks in graphene films obtained by removing PMMA carriers with acetone,which leads to an unsatisfactory conductivity and uniformity.How to obtain a graphene film with high conductivity and uniformity is very important for the development of graphene film based transparent electrodes.The surface resistance of single layer graphene films obtained by crackless transfer method ranges from 820 to 3300Ω/cm~2 with a uniformity of 18.9%.The surface resistance of single-layer graphene produced by removing PMMA with acetone is in the range of 1500 to 5500Ω/cm~2 with a uniformity of 22.9%.It can be concluded that the surface resistance of graphene films obtained by crackless transfer method is reduced by50%and the uniformity is improved by 4%compared with that obtained by the traditional method,but it has not reached the standard including the conductivity of400-500Ω/cm~2 and the uniformity of less than 7%in the commercial ITO transparent electrodes.We further optimized the process of crackless transfer method.The surface resistance of the as-produced single layer graphene ranges from 660 to 790Ω/cm~2 with a uniformity of 3.57%,while that of the four layer graphene ranges from 190 to 230Ω/cm~2with a uniformity of 2.37%.Compared with the unimproved process,the surface resistance is reduced by 71%,and the uniformity is increased by 15%.At the same time,after bending under strain of±0.6%with 10,000 bending cycles or bending time of 3000hours,the normalized surface resistances are in the range of 80%to 110%and 95%are in the range of 90%to 110%.The graphene films obtained by the optimized method show an improved mechanical stability.This is due to that the optimized approach not only improves the continuity of graphene films,but also improves the roughness of the substrate supporting the graphene films.Therefore,the optimized crackles transfer method pave a way for the application of graphene in flexible transparent electrodes.