EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Light-emitting electrochemical cells (LECs) are efficient, air-stable, low-cost, and single-layered lighting sources fabricated using sustainable solution-based techniques. They consist of two electrodes sandwiching a thin film of electroluminescent material doped with ionic electrolyte, which allows for charge transport, recombination, and light-emission processes. The most commonly employed active layer is constituted by Ir(III)-based ionic transition metal complexes (Ir-iTMCs). These reached efficacies of >50 cd/A, stabilities of thousands of hours, and luminances of 10,000 cd/m2. However, Iridium is a rare and expensive metal, and its use hampers large-scale production of LECs. As such, the search for sustainable and well-performing emitters is of utter interest. Herein, the most recent advances in our group are described.
Firstly, bright, stable, and efficient red emitting SM-LECs were achieved. They featured high irradiances (>220 μW/cm2, long stabilities of > 200 h and an external quantum efficiency (EQE) of 0.78%, which accounts for 75% of the theoretical EQE. Secondly, we reported on a hexa-peri-hexa-benzoborazinocoronene that gave rise to single-component WLECs luminances of 50 cd/m2, stabilities of 25 h and efficacy of 3.1 cd/A, and with electroluminescence spanning the whole visible range – i.e., x/y CIE coordinates of 0.29-31/0.31-38 and average color rendering index (CRI) of 87.[1] We rationalized the electroluminescence behavior consisting of a ternary emission mechanism involving fluorescence and thermally activated dual phosphorescence. The latter is enhanced by both temperature, which can be as high as 80 °C upon device driving, and electric field. This represents the first example of ternary emission activated in lighting devices.

[1] E. Fresta, J. Dosso, J. Cabanillas-Gonzalez, D. Bonifazi, R. D. Costa, Adv. Funct. Mater. 2020, 30, 1906830.