Phosphorescent sensitized fluorescent solid-state near-infrared light-emitting electrochemical cells

We report phosphorescent sensitized fluorescent near-infrared (NIR) light-emitting electrochemical cells (LECs) utilizing a phosphorescent cationic transition metal complex [Ir(ppy) ₂(dasb)] ⁺(PF ₆ ^-) (where ppy is 2-phenylpyridine and dasb is 4,5-diaza-9,9′-spirobifluorene) as the host and two fluorescent ionic NIR emitting dyes 3,3′-diethyl-2,2′-oxathiacarbocyanine iodide (DOTCI) and 3,3′-diethylthiatricarbocyanine iodide (DTTCI) as the guests. Photoluminescence measurements show that the host-guest films containing low guest concentrations effectively quench host emission due to efficient host-guest energy transfer. Electroluminescence (EL) measurements reveal that the EL spectra of the NIR LECs doped with DOTCI and DTTCI center at ca. 730 and 810 nm, respectively. Moreover, the DOTCI and DTTCI doped NIR LECs achieve peak EQE (power efficiency) up to 0.80% (5.65 mW W ^-1) and 1.24% (7.84 mW W ^-1), respectively. The device efficiencies achieved are among the highest reported for NIR LECs and thus confirm that phosphorescent sensitized fluorescence is useful for achieving efficient NIR LECs. This journal is