In this letter, the authors had quantitatively investigated the recombination zone in the mixed-host (MH) emitting layer (EML) of an organic light-emitting device with different mixed ratios experimentally and theoretically. The MH-EML consisted of a hole-transport layer (HTL) and an electron-transport layer fabricated by coevaporation. When the mixed ratio of the HTL in the EML increases, the driving voltage increases then decreases; this can be well demonstrated by an electrical model with different carrier mobilities. A blueshift was also observed due to the solid state solvation effect combined with the exciton shift from the anode to the cathode side.

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