Operando analysis for understanding the parasite exciton dynamics in blue phosphorescent OLEDs using electrically pumped spectroscopy

Investigating exciton dynamics and device physics in phosphorescent organic light-emitting diodes (Ph-OLEDs) is important for developing highly efficient devices with optimal color purity. Herein, we conduct an in-depth exploration of the recombination zone and various radiative transitions within blue Ph-OLEDs using operando electrically pumped spectroscopy. It serves as a versatile tool enabling the simultaneous analysis of time-resolved electroluminescence and photoluminescence. Our findings reveal that Ph-OLEDs with thin emission layers (3–5 nm) predominantly exhibit electromer emissions with minor interface exciplex formation, causing a reduction in efficiency. Conversely, thicker emission layers (30–40 nm) promote exciplex formation at the hole transport layer/emission layer interface, manipulating device color purity due to charge balance and recombination zone issues. Hence, electrically pumped spectroscopy is beneficial in deciphering parasitic excitons and their role in the efficiency/color purity of Ph-OLEDs. This operando investigation lays a foundation for understanding exciton dynamics and developing highly efficient device architectures.