Photo- and Electroluminescence of Doped Polymers in Langmuir-Blodgett Structures

Light emitting diodes consisting of molecular-doped polymeric LB films with alternating electron-transport and hole-transport emitting layers are first described. Electroluminescent cells were prepared using standard ITO and Mg/Ag electrodes. PMMA/PBD (1:3) composition was used to form the electron-transport layers (I). The hole-transport one (II) was formed from PVK/TPB (3% mol.). Three cell types have been studied. Two of them had the same structure ITO/II(50 nm)/I(50nm)/Mg/Ag but were prepared using different methods: spin-coating and LB technique. The third cell type had a multilayer LB structure: ITOh(10 nm)/II(4nm)/I(10 nm)/II(4 nm)/I(4 nm)/II(10 nm)/Mg/Ag. Considerable distinctions were observed in electroluminescence spectra of spin-coated and LB structures. Possible reasons for those distinctions are discussed. The multilayer LB structure was one decimal order more stable in air than the bilayer one.