Samsung Advanced Institute of Technology

Disorder-induced inhomogeneity in blue-fluorescent based organic light emitting diodes (OLEDs) based on mixtures of host and guest molecules has been studied using magneto-electroluminescence, MEL(B) response based on the so called 'Dg mechanism’, where Dg is the difference in the Land？ 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, a (<1). The carriers’ inhomogeneous response also influences the free carrier absorption spectrum, which shows characteristic properties described by a dispersive parameter b (<1). From the measured MEL(B) response at various injection conditions we found that a 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 a at low temperature indicates that the organic layer becomes more ordered, where longer-lived electron-hole spin pairs are formed.