Abstract

Nickel oxide (NiO_x) 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 NiO_x energy band for fast hole injection. After careful comparisons with pristine NiO_x and conventional MoO₃ modification layer, we demonstrate the superior capacity of AMM to precisely tune the valence band of NiO_x for efficient hole injection and thus, a balanced charge injection in the devices. As a result, we reveal the favorable energy band of NiO_x-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 NiO_x energy band for highly performing pure-blue PeLEDs.