Transparent Inverted Organic Light‐Emitting Diodes with a Tungsten Oxide Buffer Layer

Abstract

Organic light-emitting diodes (OLEDs) have already proven their readiness for commercialization in terms of lifetime and efficiency.[1] Nevertheless, it will be a challenge forOLEDs to compete against liquid-crystal displays (LCDs) for standard applications. While the angle-of-view dependency and the low contrast of liquid-crystal and plasma displays are no longer forceful arguments for OLED displays, high power efficiencies still render OLEDs a desirable display technique. Moreover, OLEDs could enable novel display applications; considerable relevance is attributed to the achievable high transparency of organic devices. The constituting layers of an OLED can be tailored to absorb only in the ultraviolet. The emission zone may exhibit a large Stokes shift. Thus, entirely see-through displays that can be integrated, for instance in automobile windshields to assist the driver, or provide additional visual information for a surgeon during a biopsy, may be realized.[2]The setup of transparent OLEDs requires transparent electrodes on the bottom and the top sides of the device. Currently, indium tin oxide (ITO) is the established conducting material, due to its high transparency. A 100 nm thick layer of ITO has a transparency above 80% throughout the visible part of the spectrum, and provides sufficiently large conductivity for OLED applications, of 20 V sq À1

Multifunctional oxides for integrated manufacturing of efficient graphene electrodes for organic electronics

“…In addition, MoO 3 and WO 3 have been identified as ITO sputtering protection layer in OLEDs and organic solar cells, where a 40-60 nm thick metal oxide layer can effectively prevent the sensitive organic layers from the high kinetic particle bombardment. [34][35][36] We note that thermally evaporated metal oxides, such as MoO 3 and WO 3 , grow as sub-stoichiometric thin film, which make these materials n-type conductive due to oxygen vacancies. 37 On the other hand, a very strong chemical reduction, e.g., as a result of high evaporation temperatures or adsorbates on the surface, leads to a different metal oxide composition with a high amount of MoO 2 and WO 2 suboxides.…”

“…37 On the other hand, a very strong chemical reduction, e.g., as a result of high evaporation temperatures or adsorbates on the surface, leads to a different metal oxide composition with a high amount of MoO 2 and WO 2 suboxides. 18,19,31,34 These species exhibit a low-band gap (<2.5 eV) leading to an increased absorption of the metal oxide films. 18,19,31,34 An O 2 plasma might partially counteract this deficiency of metal oxides.…”

Transition metal oxides on organic semiconductors

“…Recently, inverted optoelectronic devices including inverted OLEDs [25], inverted quantum dot-LEDs [26] and inverted OSCs [13,27] have been extensively studied, owning to their ability to further improve the device stability compared with conventional structures. In these devices, TMOs have been widely employed due to their capability we mentioned above that they can modify almost all electrodes for efficient hole injection/extraction.…”

Stable, Efficient, and All-Solution-Processed Quantum Dot Light-Emitting Diodes with Double-Sided Metal Oxide Nanoparticle Charge Transport Layers

“…26 Moreover, the WO 3 NPs are stable and therefore can act as a protection layer for the poly-TPD layer. 27 For the ZnO, because of the low band offset for Al/ZnO and small energetic barrier with QDs, the electron transport and injection into QDs are quite efficient. Meanwhile, ZnO with a large band gap and low-valence band level is also favorable for exciton blocking.…”