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. 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). 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. 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.
 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.
 E. Fresta, M. D. Weber, J. Fernández-Cestau, R. D. Costa, Adv. Opt. Mater. 2019, DOI: 10.1002/adom.201900830.
 J. Dosso, J. Tasseroul, F. Fasano, D. Marinelli, N. Biot, A. Fermi, D. Bonifazi, Angew. Chem. Int. Ed. 2017, 56, 4483.
 E. Fresta, J. Dosso, J. Cabanillas-Gonzalez, D. Bonifazi, R. D. Costa, Adv. Funct. Mater. 2019, under reviewer.
A new, but archetype compound [Ir(ppy-F2)2Me4phen]PF6, where ppy-F2 is 2-(2',4'-
fluorophenyl)pyridine and Me4phen is 3,4,7,8-tetramethyl-1,10-phenanthroline, was synthesized and used
to prepare a solid-state light-emitting electrochemical cell (LEC). This complex emits blue light with a
maximum at 476 nm when photoexcited in a thin film, with a photoluminescence quantum yield of 52 %.
It yields an efficient single-component solid-state electroluminescence device with a current efficiency
reaching 5.5 cd/A and a maximum power efficiency of 5.8 Lm/Watt. However, the electroluminiscence
spectrum is shifted with respect to the photoluminiscence spectrum by 80 nm resulting in the emission of
green light. We demonstrate that this unexpected shift in emission spectrum is not originating from the
way of excitation, nor from the presence of large concentrations of ions, but is related to the concentration
of the ionic transition metal complex in the thin film. The origin of the concentration dependent emission
is extensively commented and argued to be related to the population of either 3LC π-π* or 3MLCT triplet
states, in diluted and concentrated films, respectively. Using quantum chemical calculations we
demonstrate that three low-energy triplet states are present with only 0.1 eV difference in energy and that
their associated emission wavelengths differ by as much as 60 nm from each other.