Development of Vapor Deposition Processes for OLEDs
Tipus de documentTreball Final de Grau
Condicions d'accésAccés obert
This bachelor thesis describes the development of vapour deposition processes for the creation of a warm white OLED. An OLED is a layer or a stack of organic materials situated between two electrodes, which emits light when an electric current is injected into the device. The thesis starts with a short introduction about the history of the OLED, its main uses today (lightning and displays) and the disadvantages of the technology, such as lifetime, manufacturing costs and encapsulation. Right after the introduction, a set of basic concepts are introduced with the purpose of facilitating the understanding of the thesis’s contents. A short explanation about how a basic OLED stack emits light after an electron and hole recombine, is followed by a list of layers that are common to a modern OLED stack. A list of processes used during the experiments is also provided with a description for each one of them. This part ends with the introduction of some basic concepts about color and photometric quantities used during the thesis to better describe the OLEDs. Once the basic concepts have been introduced, the thesis follows by explaining the setup of the experimental environment. To operate the evaporation machine, a couple of recipes (sets of routines) have been developed for different purposes prior to the experiments. One such purpose is the calculation of the tooling factor for each of the sources, a parameter critical to the whole process to ensure that the thickness of the deposited material is the desired one. The main part of the thesis follows right after that. It describes the development of the OLED stack starting with a simple, basic stack. The first OLEDs created can be greatly improved upon by doping some of the layers to achieve better probability for electron-hole recombination. Doping the layers led to noticeable improvements in lifetime, brightness and efficiency. The next step in further improving the efficiency and changing the color of the OLED to the desired one, is to dope the emitting layer. This decision again led to many improvements related to brightness and efficiency and the discovery of possible current drain near the edges of the OLED. By creating a mask to achieve an insulation layer on the edges, this problem not only has been avoided but some efficiency and brightness improvements have been noticed again. The thesis closes with a short discussion about the results, problems encountered during the development of the thesis and a list of suggestions on how to improve the OLED’s capabilities even further.