Light-emitting electrochemical cells with ionic transition metal complexes (iTMCs) comprising the active layer have great potential for lighting applications, but to date high luminance and fast turn on times have been challenging to attain without significant loss of lifetime. Here, we demonstrate iridium iTMC devices with high luminances of 3000–5000 cd/m2, reduced turn on times, and long lifetimes through incorporation of ionic additives. Furthermore, we show additional reduction of turn on time to seconds through heat processing. We rationalize these results as the enhancement of carrier injection through improved double-layer formation at the electrodes.