New Approach Toward Fast Response Light‐Emitting Electrochemical Cells Based on Neutral Iridium Complexes via Cation Transport

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 PF 6 − . These results are presumably due to the faster delivery of the Na + ions to the electrode compared to PF 6 − 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 .