A green organic light-emitting device (OLED) with an extremely high power efficiency of over 100 lm W-1 is realized through energy transfer from an exciplex. An optimized OLED showed a maximum external efficiency of 25.7%, and a power efficiency of 79.4 lm W-1 at 1000 cd m(-2), which is 1.6-times higher than that of state-of-the-art green thermally activated delayed fluorescence (TADF) OLEDs.