Work Function-Tunable Graphene-Polymer Composite Electrodes for Organic Light-Emitting Diodes

Graphene has been regarded as one of the most promising transparent electrodes in flexible optoelectronic devices. Tremendous efforts have been paid on tuning the work function of graphene, which make significant contributions to improve the device performance. In this work, we propose to modify a single-layer graphene film with ultrathin high dielectric polymers, including poly(vinylidene chloride) (PVDC) and poly(vinylidene difluoride) (PVDF), with the dielectric constants of 4.7 and 8.4, respectively. Ultraviolet photoelectron spectroscopy confirms the formation of interfacial dipoles induced by the high dielectric polymers, and the work function can be tuned from 4.6 eV for pristine graphene to 4.72 and 4.94 eV for PVDF- and PVDC-modified graphene, respectively. Accordingly, organic light-emitting diodes (OLEDs) are fabricated, and the one based on the PVDC-modified graphene composite electrode obtained the highest current efficiency of 80.0 cd/A with a 1.27-fold enhancement compared with the pristine counterpart. This work provides an alternative strategy of interfacial dipole to the surface chemical doping method to tune the work function of graphene electrodes, and the utilization of a polymer with high dielectric constant to modify graphene successfully realized the fabrication of highly efficient OLEDs.