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Tuesday, 28 October 2014

Martijn Kemerink talks about Next generation organic electronic devices in an ICN2 Seminar

In a talk presented by Mónica Lira-Cantu, Group Leader of the ICN2 Nanostructured Materials for Photovoltaic Energy Group, the speaker discussed about devices at different levels of maturity based on (semi)conductive polymers.

Some four decades after the discovery of (semi)conductive polymers, three devices based on these materials have reached a high level of technological maturity: the organic LED, the organic solar cell and the organic field-effect transistor. At the same time there exists a large number of ‘niche devices’ at different levels of maturity, aiming for new or enhanced functionality. Many of these are hybrid devices where the aim is to combine attractive properties of organic semiconductors with those of inorganics, ferroelectrics, ions etc.

During his talk, Prof. Martijn Kemerink presented the work he leads at the Complex Materials and Devices Division of the University of Linköping (Sweden). The ICN2 Seminar was divided in three main parts: Hybrid ferroelectric/semiconducting memory; Light-emitting electrochemical cells (LECs); and, materials that harvest energy from temperature differences using the Seebeck effect. The speaker was invited and presented by CSIC Prof. Mónica Lira-Cantu, Group Leader of the ICN2 Nanostructured Materials for Photovoltaic Energy Group.

 

It is the abstract of the Seminar offered by Prof. Martijn Kemerink:

The hybrid ferroelectric/semiconducting memory that is entirely based on organic materials was introduced by Asadi et al. in 2008. To date, 1 kb arrays on this basis have been demonstrated, as are multi-level data storage and precise morphology control. Detailed understanding of the switching mechanism has been obtained using a combination of scanning probe techniques and numerical modeling. In combination, this allows making statements on attainable information densities and memory sizes using this technology.

The active layer of a light-emitting electrochemical cell (LEC) consists of an organic semiconductor and mobile ions. Field-driven redistribution of the ionic species leads to formation of a five-layered structure, with injection and transport layers sandwiching an intrinsic recombination zone. In view of the extremely complex (and expensive) layer stack used in modern OLEDs the LEC offers great potential for low-cost, large-area application. On basis of a quantitative analysis of the device and photophysics we could prove the presence of an exciton quenching process related to the inherent presence of doping. This limits the application window of LECs to applications were high-brightness is preferred over high efficiency.

In the third part, I will switch to organic materials that harvest energy from temperature differences using the Seebeck effect. This work is inspired by recently reported high Seebeck coefficients and good electrical conductivities at low thermal conductivities, leading to very promising figure-of-merit ZT values. While it will be shown that some of these results are likely flawed, insight in the charge transport mechanisms can still be obtained.