Exceeding 4% external quantum efficiency in ultraviolet organic light-emitting diode using PEDOT:PSS/MoOx double-stacked hole injection layer

Abstract

An effective and simple method has been explored to construct an efficient ultraviolet organic light-emitting diode (OLED) by incorporating poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/MoOx double-stacked hole injection layer (HIL) and slightly retarding electron injection for achieving extremely balanced charge carriers. The device produces 4.6% external quantum efficiency with an attractive ultraviolet emission peak of 377 nm and full width at half maximum of 35 nm. Ultraviolet photoelectron spectroscopy and impedance spectroscopy analysis determine the substantially enhanced hole injection capacity of PEDOT:PSS/MoOx double-stacked HIL, which accordingly contributes to optimizing carrier balance. The results pave a way to advancing OLED in potential application towards short wavelength emission.

The Feasibility of Using Magnetron Sputtered MoO x as Effective Hole Injection Layer in Organic Light-Emitting Diode

“…It is well acknowledged that the WF of MoO x interlayer plays a key role in governing hole injection characteristics, which can be facilely obtained from the secondary electron cut‐off of UPS measurement. As shown in Figure (a), the cut‐off shifts toward lower binding energy with magnetron sputtered MoO x or thermally‐evaporated MoO x covering onto ITO surface, suggesting an enhanced WF, since the WF is supposed to be the difference between the energy of He I line (21.22 eV) and the calibrated cut‐off value of UPS spectrum . Based on our UPS measurements, the WFs are estimated to be ∼5.2 eV for thermally‐evaporated MoO x and ∼5.3 eV for magnetron sputtered MoO x , which are considerably enhanced as compared with ITO (∼4.8 eV).…”

“…The wide band‐gap insulating nature of GO limits hole injection engineering . Another well acknowledged HIL is formed by vacuum thermal evaporation of extra metal oxides such as MoO x , WO 3 , NiO, and V 2 O 5 . Which are proven to be effectively enhancing hole injection from ITO anode to adjacent organic materials.…”

Aqueous Solution‐Processed Vanadium Oxide for Efficient Hole Injection Interfacial Layer in Organic Light‐Emitting Diode

“…High impedance of about 10 5 Ω and phase of about −90° are observed in the studied HODs at voltage of less than 1 V. The impedance decreases sharply and the corresponding phase transits quickly to 0° with increasing voltage. It suggests that the HOD transits from insulating state to semi‐conducting state as a result of holes injecting from ITO anode . Furthermore, in comparison with other HODs, Cell H 2 behaves the lowest transition voltage in Z–V and φ–V curves.…”

Solution‐Processed Composite Interfacial Layer of MoOx‐Doped Graphene Oxide for Robust Hole Injection in Organic Light‐Emitting Diode

“…All HOCs exhibit phase of −90° at low voltage, as shown in phase versus voltage ( φ–V ) curves in Figure (c). A transition of impedance from high to low and phase from −90 to 0° is observed with increasing voltage, indicating transiting from insulating state to semi‐conducting state . It is clear that GO + MoO x shows the lowest transition voltage in Z–V and φ–V characteristics.…”

“…Favorite HILs of transition metal oxides such as MoO x , VO x , NiO x , La 2 O 3 , and WO 3 have developed toward solubilizing in recent years. MoO x with unique energetics of high work function and strong dipole effect attracted special attention in numerous works …”