Graphene oxide/exfoliated black phosphorus van der Waals heterojunctions for PEDOT:PSS‐free‐based organic light‐emitting diodes achieving excellent electroluminescence performance

Benefiting from high transparency, good electrical conductivity, and compatibility with solution processing, poly(3,4‐ethylenedioxythiophene)‐polystyrene sulfonate (PEDOT:PSS) has become one of the most widely used interfacial materials in optoelectronic devices. However, the intrinsic acidity and hygroscopic properties of PEDOT:PSS typically cause interface deterioration and long‐term instability, significantly limiting the operational lifetime and efficiency of optoelectronic devices. Here, we report a novel two‐dimensional heterojunction assembled from graphene oxide (GO) and exfoliated black phosphorus (EBP) via van der Waals interactions, which serves as an effective hole injection layer with outstanding electro‐optical properties for high‐performance organic light‐emitting diodes (OLEDs). Employing a facile exfoliation process, well‐dispersed EBP were combined with GO at a tailored ratio, yielding an ultrahigh transmittance of 99.4% at 550 nm, a low sheet resistance of 36.7 Ω sq −1 , and a smooth surface with a root‐mean‐square roughness of 3.0 nm. The resulting GO/EBP‐based green phosphorescent OLED achieves an impressive external quantum efficiency (EQE) of 23.1% and a current efficiency as high as 79.0 cd A −1 , representing improvements of 23.5% and 21.9% over conventional PEDOT:PSS devices. Notably, the optimized devices exhibit extremely low efficiency roll‐off, maintaining an EQE of 20.9% at 1000 cd/m 2 and 18.2% even at a high luminance of 10 000 cd/m 2 . Furthermore, three large‐area Red Green Blue OLEDs (20 mm × 25 mm) and flexible white devices (25 mm × 25 mm) were successfully realized with homogeneous emission, demonstrating the extraordinary promise of GO/EBP heterojunctions in next‐generation display technologies.