Light-Emitting Electrochemical Transistors

Abstract

Since the discovery of conductive polymers in 1977, the implementation of organic conjugated materials in electronic applications has been of great interest in both industry and academia. The goal of organic electronics is to realize large-area, inexpensive and mechanicallyflexible electronic applications.Organic light emitting diodes (OLEDs), as the first commercial product made from organic conjugated polymers, have successfully demonstrated that organic electronics can make possible a new generation of modern electronics. However, OLEDs are highly sensitive to materials selection and requires a complicated fabrication process.As a result, OLEDs are expensive to fabricate and are not suitable for low-cost printing or roll-to-roll process.This thesis studies an alternative to OLEDs: light-emitting electrochemical cells (LECs). The active materials in an LEC consist of a conjugated lightemitting polymer (LEP) and an electrolyte. Taking advantage of electrochemical doping of the LEP, an LEC features an in-situ formed emissive organic p-n junction which is easy to fabricate. We aim to control the electrochemical doping profile by employing a "gate" terminal on top of a conventional LEC, forming a light-emitting electrochemical transistor (LECT). We developed three generations of LECTs, in which the position of the light-emitting profile can be modified by the voltage applied at the gate electrode, as well as the geometry of the gate materials. Thus, one can use this structure to achieve a centered light-emitting zone to maximize the power-conversion efficiency. Alternatively, LECTs can be used for information display in a highly integrated system, as it combines the simultaneous modulation of photons and electrons.In addition, we use multiple LECs to construct reconfigurable circuits, based on the reversible electrochemical doping. We demonstrate an LEC-array where several different circuits can be created by forming diodes with different polarity at different locations. The thereby formed circuitry can be erased and turned into circuitry with other functionality.For example, the diodes of a digital AND gate can be re-programmed to form an analogue voltage limiter. These reprogrammable circuits are promising for fully-printed and large-area reconfigurable circuits with facile fabrication. Exempelvis kan dioderna i en digital AND-krets programmeras om till att istället forma en analog spänningsbegränsare. Dessa programmerbara kretsar är enkla att tillverka och är därför ett lovande koncept för tryckt elektronik på stora ytor. SVENSK SAMMANFATTNING AV AVHANDLINGEN ACKNOWLEDGEMENTS

Time-Resolved Chemical Mapping in Light-Emitting Electrochemical Cells

“…PEO needs to have an operational temperature above the melting temperature (T m ) to conduct ions effectively. 43,44 In this study, we used PEO with large molecular weight (average M v = 600 000), which has a T m above room temperature; therefore, the measurements were carried out at 60 °C. Twenty line-averaged spectra (parallel to the electrodes) were extracted from each FTIR image to characterize chemical structure changes at different positions between the electrodes.…”

“…Experiments were conducted with a 4 V bias because higher applied voltages caused faster degradation of the exposed active layer due to the remaining small amount of oxygen in the purged measurement chamber. PEO needs to have an operational temperature above the melting temperature ( T m ) to conduct ions effectively. , In this study, we used PEO with large molecular weight (average M v = 600 000), which has a T m above room temperature; therefore, the measurements were carried out at 60 °C. Twenty line-averaged spectra (parallel to the electrodes) were extracted from each FTIR image to characterize chemical structure changes at different positions between the electrodes.…”