Oral: Interfacial Exciton-Polaron Quenching in Organic Light-Emitting Diodes

In organic light-emitting diodes (OLEDs), bound pairs of hole and electron polarons—termed excitons—can either recombine to emit light or be quenched through self-dissipation or non-radiative energy transfer. Among the various quenching mechanisms, exciton-polaron quenching (EPQ), where excitons transfer their energy to polarons, plays a critical role in limiting OLED performance. Most research has focused on mitigating EPQ within the bulk of the OLED emission layer (EML), as this layer contains both polarons and excitons.

In this talk, we introduce a previously overlooked yet critical form of EPQ, occurring ‘at the interface’ between the EML and adjacent charge transport layers (CTLs), termed interfacial EPQ (Inf. EPQ). When the polaron injection barrier from the CTL to the EML exceeds 0.2 eV – often seen as minor but present in most OLEDs – polarons accumulate at the interface. Excitons in the EML then transfer their energy remotely to these accumulated polarons over distances of up to 4 nm, causing significant efficiency loss. We developed a method to directly probe Inf. EPQ, identifying three key factors that govern its behavior. Our findings show that Inf. EPQ has a greater impact on OLED performance than bulk EPQ and occurs universally, across different emission wavelengths and luminescent mechanisms.

By managing Inf. EPQ, we achieved a ~70% improvement in both efficiency and lifetime of blue phosphorescent OLEDs. The discovery can directly enhance the performance of commercial OLEDs.