Flexible light-emitting diodes with EQE approaching 26.4% from horizontal dipole-oriented metal nanoclusters

Metal nanoclusters, as unique metallic molecules comprising a few to hundreds of metal atoms and stabilized by organic monolayer ligands, have recently emerged as a novel class of chromophores and hold great promise for flexible light-emitting diodes. However, the fabrication of flexible metal nanoclusters-based light-emitting diodes is still hindered by low photoluminescence quantum yields, suboptimal solution processability, and consequently compromised emitter-film quality with random dipole orientations. This work addresses these limitations through strategic molecular engineering by employing 1, 3-di(9H-carbazol-9-yl)benzene as a π-conjugated mediator. This approach enables supramolecular assembly to achieve π-π coupling-mediated horizontal dipole alignment in nanocluster solid films, allowing an external quantum efficiency of up to 26.4% in flexible light-emitting diodes with a maximum brightness of 41,365 cd m−2, and retaining more than 94% of initial efficiency after 2000 bending cycles at 3 mm curvature radius. Metal nanoclusters are promising for flexible light-emitting diodes but face efficiency and stability challenges. Here, the authors employ a π-conjugated mediator to align dipole alignment, yielding devices with 26.4% external quantum efficiency and 94% efficiency retention after 2000 bending cycles.