Bright Future for Next-Generation Organic Lighting Systems; High-performance Polymer-Based White-Light-Emitting Electrochemical Cells

Recent technological advancement has seen significant improvements in the fields of display and lighting. This has attracted significant attention of many researchers owing to the ever-increasing demand of such devices like smartphones. To this note, researchers have been looking for alternatives and have identified organic light emitting diodes as a promising solution for meeting the new applications demand. They exhibit excellent properties like flexibility and lightweight.

Among the available types of organic light emitting diodes, light-emitting electrochemical cells have remarkable advantages over the organic light emitting diodes. They can be produced in large scale at low costs and also use air stable electrode. On the other hand, polymer-based light-emitting electrochemical cells are compatible with roll-to-roll coating and solution-based screen printing. Generally, lighting and display applications require white light. White light-emitting electrochemical cells can be achieved through light mixing methods that comprises of red-green-blue. To improve their efficiency, they have been fabricated using iridium phosphorous as the guest and fluorescent conjugated polymer as the host.

Recently, a group of researchers at Waseda University: Tetsuyuki Cho, Professor Kenichi Oyaizu and Professor Hiroyuki Nishide and led by Professor Yoshinori Nishikitani in collaboration with Dr. Soichi Uchida and Dr. Suzushi Nishimura at JXTG Nippon Oil & Energy Corporation developed a white polymer-based light-emitting electrochemical cells with significantly high color rendering indices. Their research work is published in the research journal, ChemPlusChem.

Briefly, the authors commenced their experimental work by fabricating the light-emitting electrochemical cells using blended films of emitting materials consisting of red-phosphorescent iridium complexes and blue-green fluorescent polyfluorenes. They purposed to obtain very high color rendering indices and suitable Commission de Internationale de I’Eclairage coordinates through red-blue-green color mixing.

From the experimental results, the authors observed efficient energy transfer from the excited poly(9,9-dioctylfluorene-co-benzothiadiazole) to iridium complexes. This was attributed to the emission mechanism property of the light-emitting electrochemical cells. Consequently, for white light-emitting electrochemical cells, the emission color was tuned by changing the mixing ratio of materials. This was a superior advantage of utilizing mixed films of red-phosphorescent iridium complexes and blue-green fluorescent polymers as compared to single emitter systems. Furthermore, high color-rendering indices were achieved effectively using blue-green-red light mixing strategy than by using only two-color systems.

In a nutshell, the research team successfully developed white light-emitting electrochemical cells with distinct properties and efficiency as compared to the initially made organic light emitting diodes. For instance, they exhibit very high color-rendering indices which makes them a promising solution for numerous applications in lighting and displays and beyond. Therefore, light-emitting electrochemical cells based on blue-green fluorescent conjugated polymer and red iridium complexes are not only a promising solution to the design and construction of high-performance white light emitting devices but also a platform for future studies aimed at improving the functionality of such devices.