Encapsulation of OLED Devices
Introduction
Thin films and multilayer structures of organic molecules are receiving considerable attention in applications due to their exciting photonic and electronic properties. There are several reasons for this such as promises for inexpensive electronics, (short-time use and throw-away applications), integration with plastic (newspapers and video screens) and completely new applications (integration in clothes). MC2 at Chalmers University of Technology plans in the near future to draw attention to research on organic electronics. Devices of organic light emitting diodes (OLEDs) [1,2], solar cells, sensors and transistors have been demonstrated but are far from developed. The main reason is the relative limited knowledge on fabrication and especially material characterization and analysis. The sandwich-type structures of OLEDs are layers ranging from a few up to a hundred nanometers in thickness. The cathode material is often aluminium, while indium tin oxide (ITO) [3] is commonly used as anode because it is transparent and allows outcoupling of light. The substrate for organic electronic devices is usually Si-oxide, however also flexible substrates are of interest.
Aim and goal of the project
Aim of the project is to produce and optimize small-molecule devices. To be able to realize devices with long operating lifetime, low operating voltage, and a strong light emission, optimization of their physical properties and careful encapsulation are required.
In the schematic view of an organic device, the circles illustrate typical interface regions, which are crucial for a device operation, where more research is needed to solve structural and electronic problems affecting the function.
Encapsulation
layer
Scientific program
1. Growth and electrical/optical characterization of small-molecule, nm-layer structures
2. Encapsulation of organic structures
Growth and electrical/optical characterization of small-molecule layers (Applied Semiconductor Physics, MC2)
The molecular materials belong to the wide band gap semiconductors, which is the research field of the group of Applied Semiconductor Physics. We have grown small-molecule (green) OLEDs, doped organic layers with molecules synthesized at the Department of Organic Chemistry, Chalmers, and are now fabricating electronic devices. In addition growth on other substrates than ITO has been done. Some important issues that need to be addressed are: optimization of the structure for best possible performance such as long operating lifetime, low operating voltage and a strong light emission.
Encapsulation of organic structures (Electronics Production, MC2)
Organic devices are often sensitive to moisture. The presence of moisture may damage the functionality of a molecular device through hydrolysis. The objective is to formulate and characterize a low-cost and reliability encapsulation material to seal the organic devices.
In this project, we plan to formulate a Non-Conductive Adhesive Film (NCF) where we intend to use nano-sized monosphere inorganic particles to entrap the oxygen in the NCF. The fundamental idea is to form hydroxide or siloxane chains to decrease the diffusion rate of the moisture through the encapsulation layer. Several polymer resins will be tried including epoxy and acrylic systems. The formulated NCF has to meet the following requirements:
· Low moisture absorption
· Low curing temperature
· Short curing time
· Strong affinity to moisture
· Transparent to the visible light (desirable)
The developed material will be characterized using DSC, TGA and DMA. The following parameters will be characterized:
· Glass transition temperature (DMA)
· The effect of curing agents on the curing degree (DSC)
· Thermal expansion of coefficient as a function of temperature (TMA)
· Dynamic and static modulus as function of temperature (DMA)
· Polymer degradation behaviour in moisture induced environment (TGA)