Field-induced dissociation of electron-hole pairs in organic light emitting diodes monitored directly from bias-dependent magnetic resonance techniques

The conversion processes of electron-hole (e-h) pairs into carriers and excitons in organic light emitting diodes (OLEDs) have been explored by simultaneous photoluminescence-and photocurrent-detected magnetic resonance (PLDMR and PCDMR) techniques as a function of bias. Both PLDMR and PCDMR signals are shown to disappear or extremely reduce with increasing the field strength, whereas photoluminescence intensity is unchanged and photocurrent rather increases. This is clear evidence that e-h pairs are dissociated by the field. A simple model for pair dissociation is proposed and explains the field dependence of PLDMR intensity.