1, RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama, Japan
We report the application of calcium niobate (CNO) perovskite nanosheets for electron injection layers (EILs) in organic light-emitting diodes (OLEDs). Four kinds of tetraalkylammonium hydroxides having different alkyl lengths were utilized as the exfoliation agents of a layered compound precursor HCa2Nb3O10 to synthesize CNO nanosheets, including tetramethylammonium hydroxide (TMAOH), tetraethylammonium hydroxide (TEAOH), tetrapropylammonium hydroxide (TPAOH), and tetrabutylammonium hydroxide (TBAOH). CNO nanosheet EILs were applied in fluorescent poly(9,9-dioctylfluorene-alt-benzothiadiazole), poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT) polymer-based OLEDs. The effects of dispersion concentrations and alkyl chain length on the device performances were investigated. The results demonstrated that OLED performances were related to the coverage ratio of the CNO nanosheets, their thicknesses, and their workfunction values. Among the four exfoliation agents, the device with CNO nanosheets exfoliated by TPAOH showed the lowest driving voltage. The OLEDs with the CNO nanosheet EILs showed lower driving voltages compared with the devices with conventional EIL material lithium 8-quinolate.