Defect Engineering in ZnO and Ni-Doped ZnO Nanostructures for Efficient Organic Light Emitting Diode (OLED) Application

Zinc oxide has been actively studied for light-emitting diode (LED) applications and plays a pivotal role in modern lighting in both indoor and outdoor applications due to its fascinating properties. However, this material still struggles with an inefficient recombination process. This study proposes that nickel (Ni)-doped ZnO could overcome the issue in pure ZnO. In this work, pristine ZnO and Ni-doped ZnO were synthesized by the wet chemical route for organic light-emitting diode (OLED) applications. The structural and optical properties were investigated for the pristine ZnO and ZnO doped with various concentrations (0–10%) of Ni. X-ray diffraction patterns indicate that the pure and doped ZnO have a hexagonal wurtzite structure. Field-emission scanning electron microscopy (FESEM) results suggest that the pure and Ni-doped ZnO nanoparticles are spherical, and their size varies from 22 nm to 18 nm with varying concentrations of dopant. Ultraviolet (UV)-visible absorption spectroscopic results reveal the occurrence of a blue shift in the absorption edge of the pure and doped ZnO. PL spectroscopy was carried out for qualitative study of defects in the ZnO and Ni-doped ZnO. These materials were further utilized for OLED fabrication, for which the synthesized material was blended with poly[9,9-dioctylfluorenyl-2,7-diyl] (PFO). The fabricated OLED was studied by electroluminescence (EL) and I–V characteristics. The 5% Ni-ZnO/PFO showed the highest luminescence at 8 V in EL spectroscopy, which is due to the ‘e’-junction enhancement. Meanwhile, I–V characteristics showed that with up to 1% Ni-ZnO/PFO, the turn-on voltage is decreased from 5.6 V to 4.4 V, and beyond that the turn-on voltage is increased to 6.7 V compared to pure ZnO, which suggests that 1% Ni-ZnO/PFO could open the gateway for more efficient performance in OLED applications.