Pressure-assisted fabrication of organic light emitting diodes with MoO3 hole-injection layer materials

Abstract

MPa were applied to organic light emitting diodes containing either evaporated molybdenum trioxide (MoO 3) or spin-coated poly(3,4-ethylene dioxythiophene) doped with poly(styrene sulphonate) (PEDOT:PSS) hole-injection layers (HILs). The threshold voltages for both devices were reduced by about half, after the application of pressure. Furthermore, in an effort to understand the effects of pressure treatment, finite element simulations were used to study the evolution of surface contact between the HIL and emissive layer (EML) under pressure. The blister area due to interfacial impurities was also calculated. This was shown to reduce by about half, when the applied pressures were between $5 and 8 MPa. The finite element simulations used Young's modulus measurements of MoO 3 that were measured using the nanoindentation technique. They also incorporated measurements of the adhesion energy between the HIL and EML (measured by force microscopy during atomic force microscopy). Within a fracture mechanics framework, the implications of the results are then discussed for the pressure-assisted fabrication of robust organic electronic devices. V

Pressure effects on interfacial surface contacts and performance of organic solar cells

“…These can result in the increased performance of OPVs 16 and OLEDs. 5,15 Prior analytical models [18][19][20][21][22] have been used to study the surface contacts around interlocked particles during the application of pressure. Figure 1 shows the application of pressure on bilayer and complete device models with varying surface morphologies.…”

“…For a PEDOT:PSS film that forms a blister of radius, "r," upon sandwiching around a trapped particle (Fig. 1), Du et al, 5 Malyshev-Salganik et al, 21 and Wan-Mai et al 22 have idealized the contact with a penny crack in bending. Hence, by considering the relationships between the surface energies, as well as the stored energies and other variables, they were able to determine the adhesion energy (c) between the layers.…”

“…When the film's width compared with the height of the trapped particle is adequately small, then, the film will undergo stretching and bending. Hence, the total energy stored in the film (U T ) is given by Du et al 5 as…”

“…This gives high organic photovoltaic device performance. [2][3][4] Prior work [5][6][7] has explored a range of HTL materials for Organic Photovoltaics (OPVs) and Organic Light Emitting Devices (OLEDs). These include studies by Du et al, 5 Tong et al, 6 and Agyei-Tuffour et al 7 These studies have shown that the performance of different HTL materials can have significant effects on the performance of OLEDs and OPVs.…”

“…[2][3][4] Prior work [5][6][7] has explored a range of HTL materials for Organic Photovoltaics (OPVs) and Organic Light Emitting Devices (OLEDs). These include studies by Du et al, 5 Tong et al, 6 and Agyei-Tuffour et al 7 These studies have shown that the performance of different HTL materials can have significant effects on the performance of OLEDs and OPVs. Inorganic HTLs [vanadium pentoxide (V 2 O 5 ), nickel oxide (NiO), tungsten trioxide (W 2 O 3 ), and molybdenum trioxide (MoO 3 )] have also been shown to enhance the power conversion efficiencies of OLEDs, [8][9][10] while the application of pressure has been shown to enhance the surface contacts between layers in OLEDs and OPVs.…”