Improved homogeneity and surface coverage of graphene oxide layers fabricated by horizontal-dip-coating for solution-processable organic semiconducting devices

We herein report an investigation of graphene oxide (GO) thin layers fabricated by simple horizontal-dip (H-dip) coating on an indium-tin-oxide (ITO) anode as used in solution-processable organic semiconducting devices. Homogeneous and smooth GO thin films were successfully deposited via an aqueous dispersion of GO on an ITO electrode, with a high surface coverage and low surface roughness, and a thickness controlled by H-dip coating. The use of an H-dip-coated GO film as a hole-injecting interfacial layer (IFL) in organic light-emitting diodes (OLEDs) resulted in a remarkable improvement in device performance (17 cd A(-1)), better than that (12 cd A(-1)) of a reference OLED with a spin-coated GO IFL. Stacked bi-IFLs of GO/poly(ethylenedioxythiophene):poly(styrene sulfonate) (GO/PEDOT:PSS) fabricated by H-dip coating were also investigated as hole-injecting IFLs in OLEDs, and these showed an even better device performance (23 cd A(-1)). Furthermore, it was also shown that polymer solar cells with H-dip-coated GO/PEDOT:PSS hole-collecting bi-IFLs exhibited a remarkable improvement in power conversion efficiency (6.9%), which was also higher than that (4.8%) obtained with spin-coated bi-IFLs. These results clearly indicate that the H-dip-coating of GO(/PEDOT:PSS) can effectively modify the ITO interface to yield efficient hole-selective IFLs, representing considerable promise for use as an alternative to spin-coated IFLs in the mass production of solution-processable organic semiconducting devices.