An organic light-emitting device and a flat panel display, the device including an anode; a cathode; and an organic layer therebetween, the organic layer including an EML, the EML including a first host and a second host that are different from one another, a hole transport region between the anode and the EML, the hole transport region including at least one of a hole injection layer (HIL), a hole transport layer (HTL), a buffer layer, or an electron blocking layer (EBL), an electron transport region between the EML and the cathode, the electron transport region including at least one of a hole blocking layer (HBL), an electron transport layer (ETL), or an electron injection layer (EIL), and an intermediate layer between the EML and the electron transport region; wherein the intermediate layer includes a compound having an electron affinity of more than 0 eV and less than 2.5 eV.