The luminous efficiency of the organic light-emitting devices (OLEDs) with a mixed layer in a hole transport layer (HTL) and an emitting layer (EML) was highest among the fabricated OLEDs, and the luminous efficiency of the OLEDs with a mixed layer at 10 mA/cm(-2) was 6.5 cd/A. The Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of the OLEDs fabricated utilizing a mixed layer became stabilized, and the CIE chromaticity coordinates of the OLEDs at 15 V was (0.457, 0.510), indicative of a deep yellow color. The efficiency enhancement and the color stabilization of the OLEDs with a mixed layer were attributed to the exciplex emission process.