Solid-state light-emitting electrochemical cells employing phosphor-sensitized fluorescence

We report highly efficient phosphor-sensitized solid-state light-emitting electrochemical cells (LECs) utilizing a phosphorescent cationic iridium complex [Ir(dFppy)₂(SB)]⁺(PF₆^-) as the host and a fluorescent cationic dye (R6G) as the guest. Photophysical studies show that R6G retains a high photoluminescence quantum yield (PLQY) in highly polar media, revealing its suitable use as an emitting guest in an ionic host matrix. Such solid-state LECs achieve quantum efficiency (cd A^-1) efficiency, and power efficiency up to 5.5% photon/electron, 19 cd A^-1 and 21.3 lm W^-1, respectively. The device quantum efficiency achieved is among the highest reported for fluorescent LECs and is higher than one would expect from the PLQY of the R6G fluorescent dye in the host film, thus indicating that phosphor-sensitization is useful for achieving highly efficient fluorescent LECs. Moreover, using narrow-band fluorescent emitters, such as R6G (FWHM, ∼50 nm), is effective in improving the color saturation of solid-state LECs based on cationic complexes.