Abstract
(Englisch)
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Organic semiconductor devices offer the advantages of easy processing, low cost and flexibility. Light-emitting diodes (OLED), thin-film transistors (OTFT) and solar cells (OSC) have been shown so far. The demonstration of the organic injection laser have been recently withdrawn. It is the purpose of this project to explore injection lasing in organic semiconductors at the solid state. The main difficulty for realizing an organic injection laser is that the device is to support the required high current density. We tackle this problem from two sides. We maximize the current-carrying capability of the device by using charge transport crystalline organic material in a TFT configuration. Simultaneously, efforts are done to limit the required current density, by using a highly efficient energy transfer light emitting system in which the energy acceptor and emitting site is a coordinated metal complex.
Objectives:
The main objective of the project is to explore the effect of organic injection lasing that is based on organic semiconductors in solid state. On the way to realizing this objective, several results and milestones of the proposal form sub-objectives, that are extremely useful in themselves:
1. The synthesis of coordinated metal complexes with high quantum yield and low lasing threshold, where the metal can either be a rare earth or a transition metal. Such complexes are valued for efficient organic electroluminescence;
2. The realization of efficient OLEDs with the synthesized new coordinated metal complexes.
3. Achieve effective ambipolar conduction in organic crystalline solid. This is useful for organic transistors, since ambipolar conduction is a cornerstone to implement complementary logic OTFT circuits.
Work description:
Our goal is to explore the effect of organic semiconductors injection lasing. The strategy to reach this goal includes work on three levels: device structure, organic semiconductor growth and material synthesis. The device will have a transistor (TFT)-like structure. The presence of a gate will allows balancing electron and hole injection for more efficient recombination. Furthermore, the organic transport layer can be grown as a crystalline with much higher in-plane mobility than in a vertical OLED structure with amorphous organic layers. Also, the electric field in the recombination region is smaller than for OLEDs, and hence exciting breaking can be avoided. The TFT structure can include optical cladding layers. Organic semiconductor growth is the second key to the project. The current density required for lasing is much higher than for the operation of an OLED, and it can only be supported if efficient ambipolar conduction is achieved. Our goal is to achieve ambipolar conduction in organic semiconductors.
With proper growth conditions in ultra high vacuum is possible to obtain crystalline solids, which will allow ambipolar conduction to occur. The third key element that we introduce is an efficient luminescent material. Energy transfer systems that employ coordinated metal complexes as acceptor can be synthesized to be very efficient emitters. In addition, the spontaneous radiative lifetime in such complexes is long. This allows reaching the population inversion threshold more easily, and hence to reduce the lasing threshold. New complexes will be designed, synthesised and characterized. They will be used as components of a Energy transfer system where transfer of the excitation from donor to acceptor will occur by both resonant transfer and exciting diffusion.
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