Effect of residual solvent on Ru(bpy)3(ClO4)2-based light-emitting electrochemical cells

The effect of residual water (H2O) and acetonitrile (MeCN) on the performance of tris(2,2'-bipyridine)ruthenium(II) perchlorate (Ru(bpy)(3)(ClO4)(2))-based light-emitting electrochemical cells (LECs) was investigated by treating and operating the cells under high-vacuum conditions. The results show that treating the Ru(bpy)(3)(ClO4)(2) film in a conventional vacuum oven (50-100 mTorr) at 125 degrees C for 48 h is not enough to dry the films. Simply leaving the film in a high vacuum (2 x 10(-7) Torr) for 12 h raised the turn-on voltage to 2.6 V from 2.1 V and improved the device stability. After further drying of the film in an ultrahigh vacuum (UHV) chamber (6 x 10(-10) Torr) at 143 degrees C for 4 h, the film still released H2O and MeCN. When the film was baked in UHV for 24 h, the turn-on voltage rose to 6.1 V and the device was further stabilized. As indicated earlier, solvent increases the mobility of the anions and, thus, facilitates the formation of a double layer at the electrode interfaces. When the film was dried in UHV, the film resistance increased, resulting in a higher turn-on voltage with weaker emission. However, H2O also probably leads to quencher formation, so its removal increases stability.