Superb lifetime of blue organic light-emitting diodes through engineering interface carrier blocking layers and adjusting electron leakage and an unusual efficiency variation at low electric field

An extremely long lifetime blue organic light-emitting diode (OLED) was developed through managing the electron density and an S-shaped variation of efficiency in blue fluorescent organic light-emitting diodes (FOLEDs) using carrier blocking layers and systematically analyzed in conjunction with the efficiency-lifetime interrelationship. Firstly, with a sensing layer, the majority carriers in the emitting layer were identified as a function of applied voltage and found to be electrons in our FOLEDs. In our reference device, both hole and electron leakage currents are present. To analyze the influence of leakage current on the efficiency variation and lifetime in our devices, two different classes of hole blocking layers were inserted between the emitting layer and the electron transport layer. By managing electron injection into the emitting layer, we successfully and simultaneously controlled the S-shape feature in efficiency and improved the operational stability, which resulted in a state of the art blue lifetime of 300 h at 500 cd m⁻² up to 97% of the initial luminance. The lifetime of the blue FOLEDs was extended by more than 5 times by introducing an electron-leakage suppressing carrier blocking material at the interface between charge transport layers and emitting layers.