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Fluorescence quenching by electric charges is an important loss mechanism in high-brightness organic light-emitting diodes (OLEDs), but its effect is difficult to quantify in working devices. Here, we combine an electrochemical technique to control the charge density with time-resolved photoluminescence to distinguish between different quenching mechanisms. The material studied was the blue electroluminescent polymer poly(9,9-dioctylfluorene) with β-phase. Our results show that quenching occurs by Forster resonance energy transfer and is mediated by exciton diffusion. We determine the quenching parameters over a wide range of charge concentrations and estimate their impact on the OLED efficiency roll-off at high current density. We find that fluorescence quenching by charges and singlet–triplet exciton annihilation are the two main mechanisms leading to the efficiency roll-off. Our results suggest that hole polarons are not very effective quenchers of singlet excitons, which is important for understanding...

Exciton–Polaron Interactions in Polyfluorene Films with β-Phase