In conventional organic light-emitting diodes (OLEDs), current balance between electron and hole transport regions is typically achieved by leakage of the major carrier through the devices or by accumulation of the major carrier inside the devices. Both of these are known to reduce performances leading to reduction of efficiency and operation stability due to exciton-polaron annihilation, etc. We found that hole diffusion in a centimeter-scale can be achieved in a PEDOT:PSS layer via composition and interface engineering. This ultralong distance hole diffusion enables substantially enhanced hole diffusion current in the lateral direction perpendicular to the applied electric field in typical organic optoelectronic devices. By introducing this lateral hole diffusion layer (LHDL) at the anode side of OLEDs, reduced carrier accumulation, improved efficiency, and enhanced operation stability are demonstrated. The application of the LHDL provides a third strategy for current balancing with much reduced harmful effects from the previous two approaches.