Proceedings Article | 1 April 2020
Light-emitting electrochemical cells (LECs) are highly efficient, air-stable, low-cost, and single-layered lighting sources fabricated using up-scalable and sustainable solution-based techniques.[1] They consist of two electrodes sandwiching a thin film of electroluminescent material doped with ionic electrolyte, that allows for charge transport, recombination, and light-emission processes. In this context, white LECs (WLECs) still represents a challenge. Commonly, the active layer is constituted by a mixture of blue, green, red ionic transition metal complexes (iTMCs), or conjugated polymers, reaching efficacy of >10 cd/A, stability of tens of hours, and luminances of 10,000 cd/m2. Herein, the most recent advances in our group are described.
Firstly, deep-red emitting Cu-iTMCs were reported. They featured high irradiances (>100 μW/cm2, long stabilities of > 20 h and excellent color stability (x/y 0.66/0.32).[3] By combining the best performing Cu-iTMC, featuring Xantphos as P^P ligand, with the high-bandgap hole transport material 4,4′-Bis(9-carbazolyl)-1,1′-biphenyl (CBP), proof-of-concept WLECs with x/y color coordinates of 0.32/0.31, and high CRI of 92 were achieved. These results open the way to fabricate all-Cu(I) based WLECs.
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 when driven at pulsed current of 5 mA, 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.[4] 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] a) E. Fresta, R. D. Costa, J. Mater. Chem. C 2017, 5, 5643. b) R. D. Costa, Light-emitting electrochemical cells. Concepts, advances and challenges.; 1st ed.; Springer International Publishing: Basel, 2017.
[2] E. Fresta, M. D. Weber, J. Fernández-Cestau, R. D. Costa, Adv. Opt. Mater. 2019, DOI: 10.1002/adom.201900830.
[3] J. Dosso, J. Tasseroul, F. Fasano, D. Marinelli, N. Biot, A. Fermi, D. Bonifazi, Angew. Chem. Int. Ed. 2017, 56, 4483.
[4] E. Fresta, J. Dosso, J. Cabanillas-Gonzalez, D. Bonifazi, R. D. Costa, Adv. Funct. Mater. 2019, under reviewer.
