Abstract
Graphene with two-dimensional structure has attracted a significant interest due to its unique properties such as remarkable optical transmittance, electrical conductivity, and electron mobility. There are two representative methods to prepare the large-area graphene with properties suitable for organic electronics: chemical vapor deposition and solid carbon coating. In the former method, the graphene is synthesized using gasified carbon species (i.e. methane) deposited onto metal film as a catalyst at temperature as high as 800 oC. In the latter method, solid carbon sources such as polymer, graphite, and self-assembled monolayer are coated on the metal film, followed by thermal treatment at similar temperature to the former method. The graphene prepared by the methods exhibits superior properties to chemically converted graphene. However, the graphene grown on the metal substrate has to transfer on the other proper substrates such as Si wafer to apply for the electrodes of the organic electronics. The transfer process brings about the artificial defects, such as wrinkles, cracks, and vacancy, on the graphene, resulting in degradation of the graphene properties. In this study, we have introduced a novel and simple approach to prepare an atomically thin carbon nanosheet (CNS) similar to graphene properties. In addition, we have modulated the electronic properties the CNSs using chloride-based metal precursor. The CNSs were prepared using polyacrylonitrile (PAN) polymer spin-coated onto the quartz substrates. The polymer films were oxidized at 250 oC for 2 h in order to induce formation of ladder structure. The oxidized films were then heat-treated at 1150 oC under a H2/Ar mixture to promote inter- and intra-molecular bonding and remove heteroatoms bonded to the carbon atom. The structural and morphological properties of the CNS were analyzed by HR-TEM, Raman spectroscopy, XPS, and AFM. The CNS prepared using 0.5 wt% PAN solutions showed about 0.4 nm of thickness, 1600 S/cm of electrical conductivity, and 92% of transmittance. The CNS was mostly composed of sp2 carbon with a small amount of impurities such as oxygen and nitrogen analyzed by XPS. The metal ions in the precursors are easily reduced into the metal particles without post-treatment due to the electron transfer from the CNSs to the metal ions. The WFs of the CNSs doped with AuCl3, ZnCl2, and CoCl2 exhibit significantly higher values of 4.91, 4.77, and 4.69 eV, respectively, compared to the pristine CNSs (4.60 eV). The metal particles on the CNSs locally influence the electronic modification of the CNSs, leading to transparent conducting electrodes with high WFs and a high power conversion efficiency of ~ 2.01%. Therefore, we suggested that the CNS modified by metal precursor is a promising candidate as transparent and conductive electrodes for organic devices. The specific properties and the possibility of utilization of the CNS will be discussed.