Spontaneous orientation polarization (SOP) results in excess charge accumulation at the interfaces within OLEDs. The excess charge accumulation leads to significant exciton-polaron quenching (EPQ) and correlates to the device degradation. While SOP is observed in various OLED materials, the optimized SOP configuration remains not well understood. In this study, we demonstrated the correlations of the interface charge accumulation and device characteristics, particularly focusing on EPQ and device degradation, by the simultaneous measurement technique of displacement current and photoluminescence intensity (DCM-PL).
We demonstrate a method to control charge accumulation at the hetero interfaces of organic light-emitting diodes (OLEDs) using dipolar doping of hole transport layers (HTLs). Dipolar doping enables spontaneous orientation polarization (SOP) even in nonpolar HTLs, and consequently compensates the negative interface charge originating from SOP of the adjacent layer. This concept was applied to tris-(8-hydroxyquinolate) aluminum (Alq3) and tris (2- phenylpyridine)iridium (Ir(ppy)3)-based OLEDs. We confirmed that dipolar doping modifies the density and polarity of the net interface charge and reduces the luminescence loss due to both hole and electron accumulations via exciton polaron quenching.
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