Ruthenium Tetrazole-Based Electroluminescent Device: The Key Role of Counter-Ions for the Light Emission Properties

TL;DR

This study shows that using BF4- counter ions in ruthenium tetrazole complexes significantly improves the efficiency, luminance, and stability of light-emitting electrochemical cells, advancing solid-state lighting technology.

Contribution

It demonstrates the key role of BF4- counter ions in enhancing the light emission and stability of ruthenium tetrazole-based electroluminescent devices, which was not previously established.

Findings

BF4- ions reduce turn-on voltage from 7V to 5V

Complexes with BF4- show double luminance compared to neutral complexes

Enhanced stability of luminance over time with BF4- counter ions

Abstract

Light-emitting electrochemical cells (LECs), thanks to their simple device structure and the tunable emission wavelength of the light-emitting layer, are emerging as a class of electrochemical device candidate for the development of next-generation solid-state lighting. The possibility to tune on-demand the energy levels of Ruthenium(II) polypyridyl complexes, makes them ideal candidates as light-emitting layer. However, the optimization of the latter is not trivial and several issues, such as charge injection and electron and hole transport, have still to be solved to enhance the LEC performances. Here, we demonstrate how the exploitation of small counter anion (BF4-) enhances the light emission performance of ruthenium tetrazole complexes in light-emitting diodes. In comparison with neutral ruthenium tetrazole complexes, cationic Ru tetrazole ones, containing BF4- ion, show a reduction of turn-on voltage from7 to 5 V, at high luminous efficiency (1.49 cd/A) and applied voltage of 12 V, and a twofold improvement of the luminance. Moreover, complexes containing BF4- counter ion show better stability of luminance over time than other complexes without counter ion.