High efficiency and optical anisotropy in double-heterojunction nanorod light-emitting diodes

Recent advances in colloidal quantum dot light-emitting diodes (QD-LEDs) have led to efficiencies and brightness that rival the best organic LEDs. Nearly ideal internal quantum efficiency being achieved leaves light outcoupling as the only remaining means to improve external quantum efficiency (EQE) but that might require radically different device design and reoptimization. However, the current state-of-the-art QD-LEDs are based on spherical core/shell QDs, and the effects of shape and optical anisotropy remain essentially unexplored. Here, we demonstrate solution-processed, red-emitting double-heterojunction nanorod (DHNR)-LEDs with efficient hole transport exhibiting low threshold voltage and high brightness (76»000 cd m^-2) and efficiencies (EQE = 12%, current efficiency = 27.5 cd A^-1, and power efficiency = 34.6 lm W^-1). EQE exceeding the expected upper limit of ∼8% (based on ∼20% light outcoupling and solution photoluminescence quantum yield of ∼40%) suggests shape anisotropy and directional band offsets designed into DHNRs play an important role in enhancing light outcoupling.