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

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 (Sr2+)‐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 Sr2+‐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. Effective optimizations of the perovskite precursor components and the hole transport layer process have been conducted to obtain a high‐efficiency pure blue perovskite light‐emitting diode, which shows a low turn‐on voltage of 3.0 V and peak external quantum efficiency of 2.24% with good spectral stability.