Ultra-smooth and robust graphene-based hybrid anode for high-performance flexible organic light-emitting diodes

Abstract

Large surface roughness, especially caused by the large particles generated during both the transfer and the doping processes of graphene grown by chemical vapor deposition (CVD) is always a critical issue that impedes the utility of graphene in the next-generation flexible thin-film opto-electronic devices such as organic light-emitting diodes (OLEDs), because it yields pinhole defects, leakage current, and electrical shorts, etc., causing non-emitting areas and device performance degradation over time. Here, an extremely smooth and robust PEDOT:PSS/graphene/PET hybrid anode is reported, prepared by direct and polymer-free transfer of CVD-grown graphene onto the smooth PET substrate. Flexible OLEDs with such hybrid anodes have the maximum brightness, current efficiency (CE) and power efficiency (PE), as high as 19 000 cd m⁻², 76 cd A⁻¹ and 61 lm W⁻¹, respectively, which are superior to those of the ITO/glass-based OLEDs. Moreover, a 2.5-inch monolithic flexible OLED has been successfully fabricated. The luminescence is very uniform and no dark spots are observed in the unencapsulated OLEDs, demonstrating the effectiveness of our strategies and the great prospect of graphene-based flexible OLEDs in the future foldable and rollable displays.