Hole Transport Layer Modification for Highly Efficient Divalent Ion‐Doped Pure Blue Perovskite Light‐Emitting Diodes

Abstract Divalent ions‐doping has recently been developed as a new approach to blue perovskite light emitting diodes (LEDs) with improved spectral stability. However, the efficiency of these perovskite LEDs, especially in the pure blue region, is still far behind their red‐ and green‐emissive counterparts. Here, a method to improve the device efficiency of strontium ion (Sr 2+ )‐doped pure blue perovskite LEDs, prominently by modifying the hole transport layer, is reported. Mixing a small amount of poly(9,9‐di‐n‐octylfluorene‐alt‐(1,4‐phenylene‐(4‐sec‐butylphenyl)imino)‐1,4‐phenylene) (TFB) into the hole transport layer poly(9‐vinylcarbazole) (PVK) remarkably improves the morphology and reduces the trap states of Sr 2+ ‐doped perovskite films. As a result, a pure blue LED emitting at 470 nm is obtained and shows a high external quantum efficiency of 2.24% with stable electroluminescence spectra under a forward bias of up to 8 V, representing the best performance reported in the divalent ions‐doped pure blue perovskites so far. The work opens up the way for the development of efficient pure blue perovskite LEDs.