Gradient Hole\nInjection Inducing Efficient Exciton\nRecombination in Blue (475 nm) Perovskite QLEDs

Perovskite quantum dots (QDs) are emerging as excellent\nlight sources\nfor light-emitting diodes (LEDs). However, the performance of blue\nperovskite QD-based LEDs (QLEDs) still lags behind that of red and\ngreen counterparts, which is hindered by blue perovskite QDs with\nbroad bandgaps that tend to increase nonradiative recombination. Here,\nwe designed a gradient energy for hole injection utilizing multiple\nhole injection layers (HTLs) combined with carbazole-based small-molecule\nmodification to reduce the hole injection barrier between HTLs and\nQD layers and improve the hole injection efficiency, realizing efficient\nexciton recombination in blue perovskite QLEDs. Moreover, the QD film\non the designed HTLs demonstrates a lower surface roughness and improved\nphotoluminescence properties. The optimized blue CsPbCl<sub>3–<i>x</i></sub>Br<sub><i>x</i></sub> QLEDs exhibit an\nimpressive external quantum efficiency of 20.7% with an electroluminescence\npeak at 475 nm and a turn-on voltage of 2.6 V, representing the state-of-the-art\nfor blue perovskite LEDs emitting in the range of 460–480 nm.