Samsung Advanced Institute of Technology

In organic light-emitting diodes (OLEDs), understanding the efficiency loss mechanism known as exciton-polaron quenching (EPQ) has been a longstanding challenge. Traditionally, EPQ was believed to occur mainly within the bulk of the OLED emission layer (EML) due to the coexistence of polarons and excitons, limiting our understanding of its full impact. Here, we report a previously overlooked phenomenon termed "interfacial EPQ (Inf. EPQ)", which occurs at the heterointerface between the EML and the adjacent charge transport layer (CTL). We observe the direct transfer of EML excitons to CTL polarons across this interface, spanning distances of up to ？ 4 nm. Notably, Inf. EPQ exceeds EPQ within the EML bulk, even in  devices  with  a  slight interfacial  energy  barrier  (>  0.2 eV).  Our  proposed  methodology enables independent probing of Inf. EPQ, systematic validation of its essential parameters, and the identification of Dexter energy transfer as its governing mechanism. Importantly, our findings highlight Inf. EPQ as a ubiquitous phenomenon across devices with various emission wavelengths, mechanisms, and injection  levels. By effectively addressing Inf. EPQ, we achieve efficiency enhancements in red, green and blue phosphorescent OLEDs, by 70 ± 8 %, 47 ± 5 % and 66 ± 6 %, respectively. Our work advances the physical understanding of exciton and polaron dynamics at organic heterointerfaces, providing universally applicable solutions to Inf. EPQ-related issues in practical devices.