The triplet-triplet annihilation process of triplet to singlet excitons to fluorescence in polymer light-emitting diodes.

Abstract We investigate the possible triplet-triplet annihilation (TTA) process involving the conversion of triplet to singlet excitons by measuring the magnetoconductance (MC) and magnetoelectroluminescence (MEL) responses of the phenyl-substituted poly(p -phenylene vinylene) copolymer (super yellow, SY-PPV)-based polymer light-emitting diodes (PLEDs). Under low applied magnetic field (< 200 Oe), both the positive MC and MEL are observed. However, at high magnetic field (> 200 Oe), the magnitude of MEL decreases as a consequence of the decreased TTA process of triplet to singlet excitons and the fluorescence. We increase the concentration and lifetime of the triplet excitons by biasing SY-PPV-based PLEDs at the high current density and in the low temperature regime, respectively, to verify the TTA process. We observe an evident drop in MEL magnitude at 1000 Oe for the device constantly biased with 166.67 mA/cm2 at 100 K, which is correlated with the reduced TTA process under the high magnetic field. The TTA process may harvest the energy from triplet to singlet excitons in SY-PPY active layer and in part contribute the emission to fluorescence in PLEDs especially in the high current density regime. Graphical abstract Image 1 Highlights • The magnitude of MEL decreases as a consequence of the decreased TTA process of triplet to singlet excitons. • Biasing SY-PPV-based PLEDs at the high current density and in the low temperature regime increases TTA process. • TTA process harvests the energy from triplet to singlet excitons in SY-PPY active layer and in part contributes the emission to fluorescence in PLEDs. [ABSTRACT FROM AUTHOR]