Effects of charge mobilities and exciton blocking capabilities of charge blocking layers on the performance of organic light-emitting diodes

Blue thermally activated delayed fluorescence organic light-emitting diodes (OLEDs) have been fabricated using engineered charge blocking layers. It is found that the device efficiency increases with increasing the exciton blocking capability of electron blocking layer. But the device stability decreases concomitantly, mostly because the hole mobility of electron blocking layer decreases with exciton blocking capability increasing, thereby leading to the smaller width of exciton formation zone. In addition, the device stability decreases with the electron mobility of hole blocking layer decreasing, despite nearly same exciton blocking capabilities, mainly because the width of exciton formation zone decreases with the electron mobility of hole blocking layer decreasing. The width of exciton formation zone is understood based on the transit times for holes from anode to exciton formation zone and for electrons from cathode to exciton formation zone. We provide some in-depth insight useful for the delicate design of fluorescent, phosphorescent, and thermally activated delayed fluores-cence OLEDs.