We introduced Pt₃Co nanoparticles (NPs) into the hole-injection layer (HIL) in organic light-emitting devices and demonstrated a highly efficient green OLED. The Pt₃Co NPs as the hole-traps adjusted the hole transport property in the PEDOT:PSS layer, consequently resulting in a balanced charge injection into the emission layer and enhancing the efficiency of the devices. The theory analysis also indicated that the hole traps induced by Pt₃Co NPs played an important role in improving the charge balance in the Pt₃Co-containing devices. The studies on the transient resolution photoluminescence (TRPL) indicated that the lifetime of the excitons was not influenced by the Pt₃Co NPs, even though a very thin spacer was introduced. The Pt₃Co-containing device exhibited a 73% higher current efficiency compared with the conventional device without Pt₃Co NPs.