The present invention relates to a display technical field, especially to an organic light emitting device which includes from the bottom to the top: a substrate, an anode layer, a hole injection layer, a hole transport layer, an exciton blocking layer, an organic light emitting layer, an electron transport layer, an electron injection layer and a cathode layer; the material of the organic light emitting layer includes benzimidazole derivative as illustrated in Formula 1, wherein P1, P2 and P3 are benzene rings, and at least one of R1˜R12 is a substituent having hole transport ability. The present invention further provides preparing methods for the organic light emitting layer and device.