Highly Efficient Organic Light‐Emitting Diode Using A Low Refractive Index Electron Transport Layer

A low refractive index electron transport layer (ETL) can be very effective in enhancing the out‐coupling efficiency of an organic light‐emitting diode (OLED). However, most organic films show a refractive index close to 1.8. In this work, it has been discovered that tris‐[3‐(3‐pyridyl)mesityl]borane (3TPYMB) has a low refractive index of 1.65 (at 550 nm), which is the lowest refractive index ETL among the commonly used ETLs up to date. Using 3TPYMB as an ETL, a solution processed OLED is demonstrated with nearly a 76% enhancement in external quantum efficiency (EQE). Optical simulation results of this study show that 59% of the enhancement comes from the low refractive index 3TPYMB, and the remaining 17% from the change in charge balance due to the 3TPYMB ETL in the OLED devices.