Efficient single-layer OLEDs

The efficiency and stability of single-layer polymer light-emitting diodes is compromised by unbalanced charge transport, the absence of triplet-exciton harvesting and low photoluminescence quantum efficiencies. We demonstrate that using thermally delayed activated fluorescence emitters in combination with trap-free transport internal quantum efficiencies of unity are obtained, resulting in high external quantum efficiencies of 28%. Our results show that OLEDs with a simplified single-layer structure can rival the efficiencies of complex multilayer stacks.