Atomic layer deposited zirconium oxide electron injection layer for efficient organic light emitting diodes

• Published in: Organic electronics Vol. 14; no. 1; pp. 312 - 319
• Main Authors: Vasilopoulou, Maria, Kennou, Stella, Ladas, Spyridon, Georga, Stavroula N., Botzakaki, Martha, Skarlatos, Dimitrios, Krontiras, Christoforos A., Stathopoulos, Nikolaos A., Argitis, Panagiotis, Palilis, Leonidas C.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-01-2013; Elsevier
• Subjects: Applied sciences; Atomic layer deposition (ALD); Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Electron and ion emission by liquids and solids; impact phenomena; Electron injection layer; Electronics; Exact sciences and technology; Fractures; Interfaces, heterostructures, nanostructures; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Optoelectronic devices; Organic light emitting diode (OLEDs); Other materials; Photoemission and photoelectron spectra; Physics; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Specific materials; Zirconium oxide (ZrO2); Organic light emitting diode (OLEDs); Electron injection layer; Zirconium oxide (ZrO2); Atomic layer deposition (ALD); Performance evaluation; Performance characteristic; Luminous efficiency; Thin film; Atomic layer epitaxial growth; Zirconium oxide; Optoelectronic device; Low temperature; Organic electronics; Damaging; Atomic layer method; Zirconium oxide (ZrO; Frontier orbital; Oxide layer; Photoelectron spectrum; Polymer; ); Fluorene derivative polymer; Light emitting diode; Thickness; Optical measurement; Electrical measurement; Organic light emitting diodes; Conduction band; Charge carrier injection
• ISSN: 1566-1199; 1878-5530
• DOI: 10.1016/j.orgel.2012.10.006

In this work, we demonstrate that a thin zirconium oxide (ZrO2) layer formed on top of the organic semiconductor by atomic layer deposition (ALD) in low temperature performs as an efficient electron injection/hole blocking layer in organic light emitting diodes with forward architecture. The improved device performance is attributed to enhanced current injection arising from excellent energy level alignment at the F8BT/ZrO2 interface. [Display omitted]
► Atomic layer zirconium oxide deposited at low temperature. ► ZrO2 as electron injection layer. ► Energy level alignment. ► Efficient hole blocking at the F8BT/ZrO2 interface. ► Improved outcoupling efficiency.
In this work, we demonstrate efficient polyfluorene-based light emitting diodes on which conformal, thin ZrO2 layers, formed by atomic layer deposition at a relatively low temperature (175°C), in order to avoid introducing any damage in the organic under layer, efficiently inject electrons from their high lying conduction band to the polymer’s LUMO. An optimal thickness of 2nm for ZrO2 results in a threefold improvement in luminous current efficiency compared to the reference device. The relationship between the thickness of the ZrO2 layer and the device operational characteristics is further investigated and the possible reasons for the improved device performance are discussed based on the experimental results obtained by a combination of photoemission spectroscopy and electrical/optical measurements.