Solution-processed quantum dot light-emitting diodes based on NiO nanocrystals hole injection layer

Nickel oxide (NiO), as a kind of p-type transition metal oxide (TMO) has shown promising applications in photoelectric devices. In our work, the NiO nanocrystals (NCs) are fabricated by a simple solvothermal method using tert-butyl alcohol and nickel acetylacetonate as precursors at 200 °C for different reaction times. The diameters and valence band edge of the prepared NiO NCs are increased with the increase reaction time from 12 h, 24 h–36 h. The band gaps of the NiO NCs were decreased with the increase time. Selected area electron diffraction (SAED) shows that the NiO NCs is polycrystalline structure. X-ray diffraction (XRD) indicates that the NiO NCs is cubic crystal form. X-ray photoelectron spectroscopy (XPS) shows that the as-prepared NiO NCs have a core of NiO and some form of Ni2O3 and NiOOH states on its surface. Further, the obtained NiO NCs is applied on quantum dot light-emitting diode (QLED) as hole injection layer (HILs), showing excellent hole injection properties. Particularly, the NiO NCs for 24 h obtains the best results due to its high band gap and pure cubic crystal phase. Highly bright orange-red QLED with peak luminance up to ∼25580 cd m−2, and current efficiency (CE) of 5.38 cd A−1 are achieved successfully based on the high performance NiO HIL, further, the device obtained relative long operational lifetime of 11491 h, which has been improved by more than 6- fold as compared to 1839 h for the device based on PEDOT.