Disorder‐Induced Dispersive Magneto‐Electroluminescence of Blue Emitters in Organic Light Emitting Diodes

Disorder-induced inhomogeneity in blue-fluorescent-based organic light-emitting diodes (OLEDs) based on mixtures of host and guest molecules is studied using magneto-electroluminescence, MEL(B), response based on the so called “Δg mechanism”, where Δg is the difference in the Landé g-factor of electrons and holes. The disorder in the organic active layer is manifested by a unique non-Lorentzian MEL(B) response that is analyzed using a distribution of spin lifetimes for the injected electron–hole pairs that is determined by a dispersive parameter, α (<1). The carriers’ inhomogeneous response also influences the free carrier absorption spectrum, which shows characteristic properties described by a dispersive parameter β (<1). From the measured MEL(B) response at various injection conditions it is found that α is robust at increasing current density showing that the inhomogeneity is governed by intrinsic disorder in the device active layer. Also the obtained increase in α at low temperature indicates that the organic layer becomes more ordered, where longer-lived electron–hole spin pairs are formed.