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Keywords:

  • cation transport;
  • transition metals;
  • iridium complexes;
  • light-emitting;
  • organic light-emitting diodes

Abstract

Here, a new method is presented to increase the turn-on time and stability of light-emitting electrochemical cells (LECs). To this end, a neutral iridium complex (5) containing a pendant Na+ ion that is generally known to have a faster mobility in the solid film than bulky anions is introduced, instead of the classic ionic transition metal complex (iTMC) with counter anion (7). Synthesis, photophysical and electrochemical studies of these complexes are reported. In the device configuration of ITO/5 or 7+PEO (polyethylene oxide) (100–110 nm)/Au, as the voltage increases, complex 5 emits red light at −3.6 V while complex 7 appears at –5.6 V, although their electrochemical and photophysical gap are similar. Furthermore, at constant voltage, –3 V, the turn-on time of complex 5 was less than 0.5 min, which is a 60-fold faster turn-on time compared to the iTMC (7) with PF6. These results are presumably due to the faster delivery of the Na+ ions to the electrode compared to PF6 ions. Also, the device lifetime of complex 5 exhibits a six-fold increase in stability and a three-fold shorter time to reach maximum brightness at constant bias compared to the device made with complex 7.