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OLEDs are charge injection devices,which require the simultaneous injection of both electrons and holes into the electroluminescent material sandwiched between two electrodes[1].To meet this demand,two strategies including the fabrication of multilayer devices[2] and integrating hole-transporting,electron-transporting and light emitting components into a single layer[3,4],have been developed.In this work,non-doped red-emitting single-layer organic light-emitting devices based on an ambipolar small molecule,4,9-bis(4-(2,2-diphenylvinyl)phenyl)naphtho[2,3-c] [1,2,5]thiadiazole (BDPNTD)[5,6],have been studied.The hole injection barrier between ITO and BDPNTD is 0.92 eV,which is relatively large.To achieve a balance of electron and hole injection inside light-emitting layer,we inserted buffer layers,such as MoO3[7],WO3[8] and Au[9],between ITO and BDPNTD.The device configurations used in our experiments are:(i) ITO/WO3 (1 nm)/ BDPNTD (80 nm)/Mg∶Ag (10∶1,150 nm)/Ag (100 nm); (ii) ITO/MoO3 (1 nm)/BDPNTD (80 nm)/Mg∶Ag (10∶1,150 nm)/Ag (100 nm); (iii) ITO/Au (5 nm)/BDPNTD (80 nm)/Mg∶Ag (10∶1,150 nm)/Ag (100 nm).By utilizing a WO3 buffer layer,optimized single-layer device shows low turn-on voltage (2.4 V) and high luminance (4950 cd/m2) with pure red emission.