Trap-Assisted Triplet Emission in Ladder-Polymer-Based Light-Emitting Diodes

Abstract

The charge transport and recombination in light-emitting diodes (LEDs) based on a methyl-substituted poly(p-phenylene) ladder polymer (Me-LPPP) are investigated. The transport is characterized by a high room-temperature hole mobility of 2 × 10−8 m2 V−1 s−1 combined with anomalously strong electron trapping. Their electroluminescence (EL) spectrum is characterized by a blue singlet emission, a broad green featureless peak, and a yellow-orange triplet emission. The voltage dependence of the EL spectrum and negative contribution to the capacitance indicate that the triplet-emission is of trap-assisted nature, consistent with the strong electron trapping. Consequently, the color purity of the blue emissive Me-LPPP polymer LEDs can be strongly improved using trap dilution.