An organic light-emitting device and a display panel are provided. The organic light-emitting device has an anode, a cathode opposite to the anode, and a light-emitting layer between the anode and the cathode. The light-emitting layer has a host material, a light-emitting guest, and an auxiliary guest, wherein the light-emitting guest is a fluorescent dye, and the auxiliary guest is an organic substance having a thermally activated delayed fluorescence property, wherein a section in which a doping concentration of the auxiliary guest gradually increases or gradually decreases is present along a direction from the anode toward the cathode.