InP-Based Quantum Dot Light-Emitting Diode with a Blended Emissive Layer

We fabricated a homogeneous thin film by blending a hole-transporting organic molecule having long alkyl chains, N,N′-bis(3-methylphenyl)-N,N′-bis(phenyl)-9,9-dioctylfluorene (DOFL-TPD), with InP/ZnSe/ZnS quantum dots (QDs) and used it as an emissive layer (EML) in a light-emitting diode (LED). The blended QD EML-based device exhibited an external quantum efficiency of 18.6% and a maximum luminance of 128 577 cd/m2. Additionally, its operational lifetime significantly increased in comparison to that of the control devices without DOFL-TPD. We found that the uniform distribution of DOFL-TPD in the blended QD EML without any phase separation facilitated hole injection into the EML and energy transfer to QDs. Moreover, it was newly discovered that the blended QD EML suppressed electron injection into the hole transport/injection layers, thereby preventing structural degradation of the device. The homogeneously blended QD layer with an efficient charge transport material shows a strong potential to develop efficient and stable optoelectronic devices with balanced charge density.