Lateral Diffusion of Holes in Anodic Buffer Layers and Its Application in Organic Light-Emitting Diodes

In organic light-emitting diodes (OLEDs), hole transport is typically about two orders of magnitude faster than electron transport. This leads to carrier complexation near the cathode and exciton bursting on the cathode metal surface, greatly reducing the luminescence efficiency of the device. To solve this problem, we constructed a composite buffer layer of poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS) synergized with silver nanoparticles (Ag NPs) and introduced it between the anode and the organic layer, which allows the holes to diffuse laterally under the influence of the concentration gradient, so that the luminescent region extended beyond the overlap of the cathode–anode. The lateral diffusion of holes can reduce the accumulation of holes in the device and improve the device stability. More importantly, adding the material C₇₀ with a high highest occupied molecular orbital (HOMO) energy level to form a heterojunction in this buffer layer can further control the lateral diffusion distance and the longitudinal injection rate of holes; when the ratio of the two is 1:1, the carrier balance of the OLED is optimal, and the optical performance is excellent. This work provides a new strategy for OLED current balancing and opens up a new avenue for fabricating high-efficiency OLEDs.