Sufficient\nHole Injection for High-Performance Blue\nPerovskite Light-Emitting Diodes

Nickel\noxide (NiO<sub><i>x</i></sub>) has been extensively\nadopted as a promising hole transport material for perovskite light-emitting\ndiodes (PeLEDs). However, its shallow valence band induces a large\nhole injection barrier for pure-blue PeLEDs with moderate device performances.\nHerein, an ingenious interface layer of ammonium molybdate (AMM) is\nproposed to successfully tailor the NiO<sub><i>x</i></sub> energy band for fast hole injection. After careful comparisons with\npristine NiO<sub><i>x</i></sub> and conventional MoO<sub>3</sub> modification layer, we demonstrate the superior capacity\nof AMM to precisely tune the valence band of NiO<sub><i>x</i></sub> for efficient hole injection and thus, a balanced charge injection\nin the devices. As a result, we reveal the favorable energy band of\nNiO<sub><i>x</i></sub>-AMM for one of the best-performing\npure-blue PeLEDs with an impressive efficiency of 9.15% at 473 nm\nand a high brightness of 5550 cd m<sup>–2</sup>. More importantly,\nwe demonstrate a remarkably low turn-on voltage of 2.4 V, being the\nsmallest turn-on voltage for pure-blue PeLEDs through a sufficient\nhole injection. Consequently, this work contributes to a feasible\nand efficient approach to tailor the NiO<sub><i>x</i></sub> energy band for highly performing pure-blue PeLEDs.