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Towards Long-lived and Efficient Organic Light-emitting Electrochemical Cells

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Ground-breaking research for efficient long-life lighting

Thanks to their good electroluminescence efficiency, there is increasing interest in organic 'Light-emitting electrochemical cells' (LECs) as solid-state luminescence sources. New research reveals how to further improve efficiency and what limits the lifetime of this optoelectronic device.

Energy

Generating light from either electrical energy or chemical reactions, LECs hold great promise for diverse applications such as large-area lighting. Despite the technology's high potential for smarter energy management compared to incandescent light bulbs, limited device lifetime and efficiency hold back widespread use. Within the EU-funded LEOLEC (Towards long-lived and efficient organic light-emitting electrochemical cells) project, scientists thoroughly studied factors affecting the position of the illumination zone, which is key to understanding what limits organic LEC lifetime. The team prepared LECs using several different light-emitting polymers, seeking to understand why light emission usually takes place close to the cathode. They concluded that the LEC emission position largely depends on the negatively charged carriers in the light-emitting polymer. For example, for a polymer containing oxygen elements, light emission takes place close to the cathode. For another polymer containing only hydrogen and carbon, light emission takes place at a different position – in the middle of the two conductive electrodes. Scientists demonstrated a novel approach to improve the efficiency of white-light organic LEC devices by incorporating protein polymers into the device. They successfully prepared a novel light-emitting device, where emission stemmed from a very thin layer of fibrils containing emissive metal complexes. Photophysical experiments shed further light on the exact protein function. As organic LEC technology features novel form factors such as flexibility and large-area emission, this newly developed method is compatible with printing processes. Project work took a step closer to understanding the charge-generation mechanism in organic solar cells. Scientists measured the cell open-circuit voltages at different temperatures and compared different donor-acceptor interfaces. Results demonstrated a decrease in open-circuit voltage at low temperatures. Reduced charge separation at low temperatures accounted for this decrease. LEOLEC findings should help research reach a point where LEC energy efficiency and lifetime will make them useful for commercial applications. Findings are also expected to increase European Research Area (ERA) competitiveness in the organic LEC field.

Keywords

Lighting, light-emitting electrochemical cells, polymers, charge-generation

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8 June 2020