Triplet dynamics and charge carrier trapping in triplet-emitter doped conjugated polymers

Abstract

Phosphorescent (Ph) properties and charge carrier trapping have been studied in conjugated polymer CNPPP with incorporated red-emitting Btp 2Ir(acac) metal–organic complex by time-resolved photoluminescence and thermally-stimulated luminescence (TSL) techniques. We characterized intrinsic Ph of CNPPP matrix and dynamics of triplet excitations of Btp 2Ir(acac) confined by the polymer host. Combined studies of time and intensity dependence of guest Ph have demonstrated that the observed decrease in the Ph efficiency in CNPPP:Btp 2Ir(acac) system at increasing excitation intensity is dominated by mutual host–guest triplet–triplet annihilation. We observed Ph spectral diffusion effects at 10 wt.% of Btp 2Ir(acac) dispersed in a polymer matrix, which is a proof for the triplet excitons migration though the manifold of triplet-emitter sites, and which governs the Ph concentration quenching effect. TSL measurements have provided direct evidence that the triplet-emitter molecules create a deep charge trap in the conjugated polymer and allowed trap characterization.