Transition Metal Oxides for Organic Electronics: Energetics, Device Physics and Applications

Abstract

During the last few years, transition metal oxides (TMO) such as molybdenum tri-oxide (MoO(3) ), vanadium pent-oxide (V(2) O(5) ) or tungsten tri-oxide (WO(3) ) have been extensively studied because of their exceptional electronic properties for charge injection and extraction in organic electronic devices. These unique properties have led to the performance enhancement of several types of devices and to a variety of novel applications. TMOs have been used to realize efficient and long-term stable p-type doping of wide band gap organic materials, charge-generation junctions for stacked organic light emitting diodes (OLED), sputtering buffer layers for semi-transparent devices, and organic photovoltaic (OPV) cells with improved charge extraction, enhanced power conversion efficiency and substantially improved long term stability. Energetics in general play a key role in advancing device structure and performance in organic electronics; however, the literature provides a very inconsistent picture of the electronic structure of TMOs and the resulting interpretation of their role as functional constituents in organic electronics. With this review we intend to clarify some of the existing misconceptions. An overview of TMO-based device architectures ranging from transparent OLEDs to tandem OPV cells is also given. Various TMO film deposition methods are reviewed, addressing vacuum evaporation and recent approaches for solution-based processing. The specific properties of the resulting materials and their role as functional layers in organic devices are discussed.

Transition metal oxides as hole-selective contacts in silicon heterojunctions solar cells

“…By comparing with a-Si:H (calculated from extinction coefficient data [35]), all three oxides are less absorbent up to ~600 nm in wavelength, while MoO x is the most transparent. In parallel, electrical measurements of the oxide films at room temperature yielded rather low lateral conductivities (σ V2Ox ~8 x10 -8 S/cm, σ MoOx ~1.8 x10 -7 S/cm and σ WOx ~1.1 x10 -7 S/cm) in accordance with previous reports [9,18]. These results limit the oxide thickness on the final device to only a few nanometers and justifies the need for an ITO collecting electrode.…”

“…Another kind of materials that have demonstrated excellent carrier-selective properties are transition metal oxides (TMOs), wide bandgap semiconductors with a distinctive p-or n-type character and a broad range of work functions varying from 2 to 7 eV [9]. Many reports can be found in the literature regarding interface engineering with TMOs applied to organic light emitting diodes (OLEDs) and organic solar cells [10], such as molybdenum trioxide (MoO 3 ) [11], tungsten trioxide (WO 3 ) [12], vanadium pentoxide (V 2 O 5 ) [13] and rhenium trioxide (ReO 3 ) [14].…”

Transparent Electrodes for Efficient Optoelectronics

“…[181,182] Figure 4. a) Silicon heterojunction (SHJ) solar cell structure and b) zoom-in of the front TCO layer indicating the 1. metal/TCO interface, 2. bulk and 3.…”

Processing and charge state engineering of MoOx

“…This material system, particularly in the form of thin and ultra-thin films, finds applications in a variety of technologically relevant fields, including catalysis, 1 gas sensors, 2,3 optically switchable coatings, 4,5 high-energy density solid-state microbatteries, 6,7 smart windows technology, 8,9 flexible supercapacitors, 10 thin film transistors (TFTs) 11 and organic electronics. [12][13][14][15][16][17][18][19][20][21][22] Owing to its high work function -up to 6.9 eV [12] and to the layered structure of α-MoO 3 , MoO x is also employed as a 2D material beyond graphene and as efficient hole contact on 2D transition metal dichalcogenides for p-type field effect transistors (p-FETs). [23][24][25] In view of a reliable device performance, the control over the chemical and physical properties of the MoO x system is mandatory.…”