Efficient and Long‐Living Light‐Emitting Electrochemical Cells

Abstract

Three new heteroleptic iridium complexes that combine two approaches, one leading to a high stability and the other yielding a high luminescence efficiency, are presented. All complexes contain a phenyl group at the 6‐position of the neutral bpy ligand, which holds an additional, increasingly bulky substituent on the 4‐position. The phenyl group allows for intramolecular π–π stacking, which renders the complex more stable and yields long‐living light‐emitting electrochemical cells (LECs). The additional substituent increases the intersite distance between the cations in the film, reducing the quenching of the excitons, and should improve the efficiency of the LECs. Density functional theory calculations indicate that the three complexes have the desired π–π intramolecular interactions between the pendant phenyl ring of the bpy ligand and the phenyl ring of one of the ppy ligands in the ground and the excited states. The photoluminescence quantum efficiency of concentrated films of the complexes improves with the increasing size of the bulky groups indicating that the adopted strategy for improving the efficiency is successful. Indeed, LEC devices employing these complexes as the primary active component show shorter turn‐on times, higher efficiencies and luminances, and, surprisingly, also demonstrate longer device stabilities.

Highly Stable and Efficient Light-Emitting Electrochemical Cells Based on Cationic Iridium Complexes Bearing Arylazole Ancillary Ligands

“…23,29 However, bulky groups are known to slow down the migration of the ions in the device inducing long turn-on times. 30,31 Hence, there is still room to explore new strategies and ligands in search for higher performances and stabilities. In this work, we introduce a series of new complexes with arylazole-based ancillary ligands without bulky groups, and use them to prepare LEC devices trying to reach high stabilities without affecting the turn-on times.…”

Transient and d.c. analysis of the operation mechanism of light-emitting electrochemical cells

“…-Organic light-emitting devices constitute an important branch in organic optoelectronics due to their great potential to be used in a wide range of applications, from dot-pixels for color displays to large-area panels for ambient illumination [1][2][3][4][5][6]. Differently from organic/polymeric light-emitting diodes (OLEDs/PLEDs), whose technology is already quite well developed, polymeric light-emitting electrochemical cells, LECs [7], are devices whose performance is still not satisfactory for commercial applications, but had presented a growing interest in recent years [8][9][10][11][12]. The main feature of a LEC is that the active layer comprises a blend of a conjugated electroluminescent polymer (EP) and a polymer electrolyte, which confers to them advantageous characteristics like bipolar operation (in forward or in reverse bias) and low operating voltages, regardless of the work function of the electrodes and of the thickness of the active layer [7].…”

On-demand photochemical stabilization of doping in light-emitting electrochemical cells

“…[12][13][14] The light-emitting electrochemical cell (LEC) comprises a blend of a conjugated polymer and mobile ions as the active material sandwiched between two electrodes. [15][16][17][18][19][20][21][22][23][24][25] An LEC actually makes use of the mobility of the ions for the in-situ electrochemical formation of doped conjugated polymer regions at the electrode interfaces, and the subsequent establishment of a light-emitting p-n junction within the bulk of the active material, under the direction of an externally applied voltage. [26,27] However, the pn junction in LECs is dynamic and only stable as long as the applied voltage remains, and for applications where a fast, repeatable response and rectification of current and light emission are required this represents a problem.…”