Organic light emitting devices (OLEDs) are described, the OLEDs comprising an anode; a cathode; and an organic region, disposed between the anode and the cathode, comprising a first complex and a second complex; wherein when a voltage is applied across the anode and cathode at room temperature, the OLED emits a luminescent radiation that comprises one or more luminescent radiation components resulting from the formation of at least one exciplex; wherein the exciplex is formed by at least one of the following aggregate types: 1) at least one aggregate within the first complex, and at least one aggregate within the second complex; 2) at least one aggregate between the first and the second complex; and 3) both 1 and 2.