Sufficient Hole Injection for High-Performance Blue Perovskite Light-Emitting Diodes

Nickel oxide (NiOx) has been extensively adopted as a promising hole transport material for perovskite light-emitting diodes (PeLEDs). However, its shallow valence band induces a large hole injection barrier for pure-blue PeLEDs with moderate device performances. Herein, an ingenious interface layer of ammonium molybdate (AMM) is proposed to successfully tailor the NiOx energy band for fast hole injection. After careful comparisons with pristine NiOx and conventional MoO3 modification layer, we demonstrate the superior capacity of AMM to precisely tune the valence band of NiOx for efficient hole injection and thus, a balanced charge injection in the devices. As a result, we reveal the favorable energy band of NiOx-AMM for one of the best-performing pure-blue PeLEDs with an impressive efficiency of 9.15% at 473 nm and a high brightness of 5550 cd m–2. More importantly, we demonstrate a remarkably low turn-on voltage of 2.4 V, being the smallest turn-on voltage for pure-blue PeLEDs through a sufficient hole injection. Consequently, this work contributes to a feasible and efficient approach to tailor the NiOx energy band for highly performing pure-blue PeLEDs.