Dual-functioning displays, which can simultaneously transmit and receive information and energy through visible light, would enable enhanced user interfaces and device-to-device interactivity. We demonstrate that double heterojunctions designed into colloidal semiconductor nanorods allow both efficient photocurrent generation through a photovoltaic response and electroluminescence within a single device. These dual-functioning, all-solution-processed double-heterojunction nanorod light-responsive light-emitting diodes open feasible routes to a variety of advanced applications, from touchless interactive screens to energy harvesting and scavenging displays and massively parallel display-to-display data communication.

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.

As semiconductor heterostructures play critical roles in today's electronics and optoelectronics, the introduction of active heterojunctions can impart new and improved capabilities that will enable the use of solution-processable colloidal quantum dots in future devices. Such heterojunctions incorporated into colloidal nanorods may be especially promising, since the inherent shape anisotropy can provide additional benefits of directionality and accessibility in band structure engineering and assembly. Here we develop doubleheterojunction nanorods where two distinct semiconductor materials with type II staggered band offset are both in contact with one smaller band gap material. The double heterojunction can provide independent control over the electron and hole injection/ extraction processes while maintaining high photoluminescence yields. Light-emitting diodes utilizing double-heterojunction nanorods as the electroluminescent layer are demonstrated with low threshold voltage, narrow bandwidth and high efficiencies.

In the synthesis of anisotropic colloidal nanocrystal heterostructures, the interplay between many complicating factors such as interfacial chemistry, lattice strain, and coordinating ligands can make precise control over spatial distribution of composition extremely challenging. However, understanding how each complicating factor contributes to the growth mechanism can lead to otherwise difficult-to-achieve or unique structures and the means to tune their electronic/optical properties. Here, we report on the effects of lattice strain and the choice of ligands on the formation of Cu 2−x S/I-III-VI 2 colloidal nanorod heterostructures through partial cation exchange starting from Cu 2−x S nanorods. Lattice strain can induce alternating Cu 2−x S/CuGaS 2 segments along a colloidal nanorod if CuGaS 2 can nucleate easily from the sides of the nanorods. The choice in coordinating ligands can alter this preference to favor tip nucleation, in which case the resulting heterostructure has CuGaS 2 /Cu 2−x S/CuGaS 2 rod/rod/rod geometry. In the less strained CuInS 2 case, superlattice-like alternating segmentation does not occur but the ligand induced difference in the preference of where nucleation initiates can still lead to distinct heterostructure morphologies. These results demonstrate how surface accessibility varied by the choice of ligands can be exploited synergistically with the driving force that creates interfaces to provide synthetic control over nanoscale heterostructure formation.

Controlling the crystal structure and shape and/or faceting of colloidal nanocrystals during growth through easily variable reaction parameters is highly desirable. The choice of precursors is one such parameter that can significantly impact achievable shapes and phases. Here, we examine how different Cu precursors in the synthesis of colloidal copper sulfide nanocrystals affect the resulting shape and crystal phase. An observed decreasing aspect ratio in one-dimensional nanorods (eventually transitioning to two-dimensional nanodisks) is consistent with the expected effects of decreasing Cu precursor reactivity. Nanorods are predominantly chalcocite at the early stages of growth, but a phase transition to djurleite occurs and is accompanied by a change in tip faceting upon further growth. In contrast, nanodisks appear in the djurleite phase early on and remain so upon continued growth. Localized surface plasmon resonance in various shapes of nanocrystals achieved is enhanced with chemical oxidation, and the near-field enhancement is also simulated.