Research of electroluminescent materials for use in optoelectronic devices

The main goal of the project was to provide spectroscopic characteristics of electroluminescent materials that can be of potential use in optoelectronic devices, such as organic light emitting diodes (OLED) and organic light-emitting transistors (OLEFET). The latter are a new generation of devices that combine emission properties of OLED and typical electrical properties of field effect transistors. Materials used in organic electronics must meet numerous conditions. Chief among them are high solid-state emission efficiency, good conductivity capabilities (for holes and electrons alike), the capability to form thin layers, thermal stability, resistance to oxygen and humidity, and emitted light colour purity.

With a view to developing the proper active layer for optoelectronic devices, several materials have been scrutinized, including small-molecule ones and polymers. In order to verify the legitimacy of their use as emitters in light-emitting devices, photophysical research has been conducted in solution and in solid state.

In the project, particular attention has been paid to host-guest systems, in which light-emitting dopant have been dispersed in a polymer matrix. In order to learn the mechanism of energy transfer between the molecules of the matrix and those of the emitter, detailed spectroscopy studies have been conducted: measurements of steady-state and time-resolved fluorescence with determining emission quantum yield , supplemented with studies of spectrally-resolved thermoluminescence. It has been established that the right match of energy levels of the matrix and the guest ensures effective energy transfer and results in efficient luminescence of the emitter. The most promising systems have been tested as active layers in the produced and characterized OLEDs.

Attempts have been made to develop an ambipolar material and use it in a horizontal light-emitting field-effect transistor. Tests have been carried out both on one-component organic layers and on blends composed of n- and p-doped semiconductors.  An alternative solution aimed at the creation of a light-emitting transistor has also been proposed. A vertical transistor with an evaporated gate electrode inserted between the hole and the electron transporting layers  has been constructed and characterised, its materials selected in such a way as to enable it to create a light-emitting exciplex. A method of controlling the current and the colour of the emitted light in a vertical organic field-effect transistor has been developed.  

The results of the project’s research will help in understanding the mechanisms of physical processes such as excitons formation and their radiative recombination, lying at the foundations of the operation of electroluminescent devices. The knowledge gathered in the course of the research can be used in designing and producing more efficient optoelectronic devices.

Dr. Eng. Gabriela Wiosna-Sałyga

Graduated from the Faculty of Chemistry, Lodz University of Technology. In 2009 she received her doctorate in chemistry at the Institute of Physical Chemistry of the Polish Academy of Sciences for her research on the relations between the structure, dynamics and reactivity of organic molecules, including systems with the hydrogen bond. Dr Gabriela Sałyga-Wiosna’s current interests concentrate on spectroscopy (in particular, emission spectroscopy) of materials that are of potential use for optoelectronics. She is involved in development, production and characterisation of optoelectronic devices (mainly OLEDs) and research on the mechanisms of processes responsible for effective emission of light in this category of devices.

Date of publication: 18^th Nov, 2016