Tiffany Tong

Adhesion in organic electronic structures

This paper presents the results of atomic force microscopy (AFM) measurements of the adhesion between materials relevant to organic solar cells and organic light-emitting devices. The adhesion is quantified using pull-off forces obtained for organic-organic, organic-inorganic, and inorganic-inorganic interfaces. The measured pull-off forces and surface parameters are then incorporated into theoretical models for the estimation of surface energies. The implications of the results are then discussed for the design of enhanced robustness in organic electronic structures.

Adhesion and cyclic stretching of Au thin film on poly(dimethyl-siloxane) for stretchable electronics

This paper presents the results of an experimental study of the effects of cyclic damage and adhesion on nanoscale Au thin films deposited on a flexible poly(dimethyl-siloxane) substrate. The deformation and cracking mechanisms are elucidated as functions of film thickness. The implications of the results are also discussed for the design of stretchable electronic structures.

Adhesion in flexible organic and hybrid organic/inorganic light emitting device and solar cells

This paper presents the results of an experimental study of the adhesion between bi-material pairs that are relevant to organic light emitting devices, hybrid organic/inorganic light emitting devices, organic bulk heterojunction solar cells, and hybrid organic/inorganic solar cells on flexible substrates. Adhesion between the possible bi-material pairs is measured using force microscopy (AFM) techniques. These include: interfaces that are relevant to organic light emitting devices, hybrid organic/inorganic light emitting devices, bulk heterojunction solar cells, and hybrid combinations of titanium dioxide (TiO2) and poly(3-hexylthiophene). The results of AFM measurements are incorporated into the Derjaguin-Muller-Toporov model for the determination of adhesion energies. The implications of the results are then discussed for the design of robust organic and hybrid organic/inorganic electronic devices.

Adhesion and degradation of organic and hybrid organic-inorganic light-emitting devices

This paper presents the results of a combined analytical, computational, and experimental study of adhesion and degradation of Organic Light Emitting Devices (OLEDs). The adhesion between layers that are relevant to OLEDs is studied using an atomic force microscopy technique. The interfacial failure mechanisms associated with blister formation in OLEDs and those due to the addition of TiO2 nanoparticles into the active regions are then elucidated using a combination of fracture mechanics, finite element modeling and experiments. The blisters observed in the models are shown to be consistent with the results from adhesion, interfacial fracture mechanics models, and prior reports of diffusion-assisted phenomena. The implications of the work are then discussed for the design of OLED structures with improved lifetimes and robustness.

A Study of Factors that Influence the Adoption of Solar Powered Lanterns in a Rural Village in Kenya

The problem of access to electricity is still a major challenge to about 2 billion people that still live in rural and urban off-grid areas on incomes of

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

1-2/day. Since the cost of linking these people to the grid is high, there is a need to explore the development of alternative energy solutions for the provision of electricity in such contexts. There is also a need to develop new insights for the formulation of evidence-based policy that could enable the development of strategies to provide electricity to people that live in off-grid areas. This paper presents the results of a survey that provides insights for the formulation of evidence-based policy for the adoption of solar lanterns into rural/urban off-grid areas. The two year questionnaire study was carried out in Mpala Village in the Laikipia district of Kenya. The study identifies the factors that resulted in the adoption rate of 96% and a decrease of 14.7% in annual family expenditures. The social and health impacts are also elucidated before discussing the implications of the results for the formulation of evidence-based solar energy policy in developing countries.

Pressure Effects on the Lamination of Organic Light-Emitting Diodes

In this study, pressures of ∼5 to ∼8 MPa were applied to organic light emitting diodes containing either evaporated molybdenum trioxide (MoO3) 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 Youngs modulus measurements of MoO3 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)....

Dendrite growth in annealed polymer blends for use in bulk heterojunction solar cells

This paper presents the results of finite element simulations of the lamination process for the fabrication of organic light-emitting diodes (OLEDs). The simulations utilize mechanical properties of the individual layers of the OLED structures that are obtained using nanoindentation techniques. The simulations show that applied pressure can cause contact evolution and sink-in around dust particles that are interposed between the organic materials layers, or the organic/inorganic layers. The implications of the results are discussed for the fabrication of robust OLEDs.

Thermally induced surface instabilities in polymer light emitting diodes

This paper presents the evidence of growth of dendrites during the annealing of poly (3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) blends that are being explored for potential applications in bulk heterojunction polymer solar cells. These dendrites were observed in high resolution scanning electron microscopy to have morphologies that depend on the annealing temperature. Consistent with a recent eutectic phase diagram, the dendrites were not observed at 200 °C. The observations were explained by considering the effects of temperature on the kinetics of phase nucleation and growth in P3HT: PCBM blends. The implications of the results are also discussed for the stability of electrical properties in bulk heterojunction solar cells.

Mode Mixity Dependence of Interfacial Fracture Toughness in Organic Electronic Structures

The role of thermal gradients and their attendant mechanical stresses in the overall stability of organic electronic devices has been elucidated through the occurrence of spiral shaped blisters that develop on the surface of suitably biased polymer light emitting diodes. A model based on the spontaneous disordering (or ordering) of polymeric thin film systems has been used to explain the formation and growth of these blisters. The model is shown to provide insights into how thermal stresses affect the overall stability of organic electronic devices. The implications of the results are then discussed for the design of flexible organic electronic devices.