Highly efficient inverted blue light-emitting diodes by thermal annealing and interfacial modification

Inverted polymer light-emitting diodes (IPLED) were fabricated by using polyfluorene (PF-FSO10) as the emissive layer, polyethyleneimine ethoxylate (PEIE) as the interlayer, and 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI) as the electron-transport layer with the configuration of ITO/ZnO/PEIE/TPBI/PF-FSO10/MoO3/Al. Thermal annealing PF-FSO10 made the hole transporting ability decreased, the electron transporting ability enhanced, and thus, jointly promoted the carrier balances in the emissive layer. Inserting a TPBI layer between the PEIE and PF-FSO10 much enhanced the electron transportation and reduced the exciton quench on the ZnO interface. Therefore, the inverted blue light-emitting diode was obtained with a luminous efficiency of 6.8 cd A−1 (an external quantum efficiency of 7.1%), and the CIE color coordinates of (0.15, 0.15), which was among the highest efficiency values in solution-processed inverted blue fluorescent light-emitting diodes.