In-operando investigation of Purcell effect on efficiency roll-off in top-emitting phosphorescent organic light emitting diodes

Efficiency roll-off is a major issue for applications of organic light emitting diodes (OLEDs) that require high brightness. The underlying processes leading to efficiency roll-off in phosphorescent OLEDs include triplet-polaron (TPA) and triplet-triplet annihilation (TTA). Hence, decreasing the triplet exciton lifetime by enhancing radiative decay rates can be an effective method to manage efficiency roll-off in phosphorescent OLEDs. Here we use in-operando measurement to study the Purcell effect and engineer efficiency roll-off. By changing the cavity parameters and measuring electroluminescence (EL) and photoluminescence (PL) on operating devices, we find that devices with higher Purcell factor have a smaller efficiency roll-off, suggesting a route to improve the performance of OLEDs in high brightness applications.