Investigation of improving organic light-emitting diodes efficiency using an ultra-thin ultraviolet-ozone-treated Nb-doped ZnO film as anode buffer layer

In this study, ultraviolet (UV)-ozone treated ultrathin Nb-doped ZnO (NZO) films are developed as an efficient anode buffer layer to improve the overall performance of organic light-emitting diodes (OLEDs). The results show that the UV-ozone treated NZO buffer layer containing 1 mol% of Nb2O5 possesses a higher oxygen content and a greater work function (5.22 eV) as compared to that of an indium tin oxide (ITO) film (similar to 4.7 eV) signifying a reduction in hole injection barrier and thus an improvement in the injection efficiency. In addition, UV-ozone treatment can increase the surface energy of NZO films while reducing their surface roughness. Importantly, the UV-ozone treated 1 nm-thick NZO film with a Nb2O5 doping concentration of 1 mol% can help to lower the turn-on voltage from 3.2 V to 2.8 V, increase the luminance from 10,450 cd/m(2) to 25370 cd/m(2), and improve the current efficiency from 3.46 cd/A to 5.26 cd/A, (similar to 52 % enhancement as compared to the standard OLED device). Moreover, OLEDs with the developed buffer layer reveal a significant improvement in the roll-off phenomenon under high current densities, indicating a key role of the optimized NZO film in enhancing the carrier balance of the devices. When applied to the p-i-n structure, the NZO film also lead to a superior device performance as compared to the conventional p-i-n structure using NPB:MoO3 as a hole injection layer, suggesting a widespread use of the developed thin film. These findings therefore show a promising use of the UV-ozone treated NZO ultrathin film as an effective anode buffer material for enhancing OLED overall performance. (C) 2022 Published by Elsevier B.V.

Automated summary

Ultraviolet (UV)-ozone treated ultrathin Nb-doped ZnO (NZO) films can act as efficient anode buffer layers to enhance the overall performance of organic light-emitting diodes (OLEDs). The UV-ozone treatment increases the oxygen content and work function of the NZO films, leading to a reduction in hole injection barrier and improved injection efficiency. Moreover, the treatment improves the surface energy and reduces the surface roughness of the NZO films, resulting in lower turn-on voltage, higher luminance, and improved current efficiency in the OLEDs.