Organometal halide perovskite has recently emerged as a very promising family of materials with augmented performance in electronic and optoelectronic applications including photovoltaic devices, photodetectors, and light-emitting diodes. Herein, we propose and demonstrate facile solution synthesis of a series of colloidal organometal halide perovskite CH3NH3PbX3 (X = halides) nanoparticles with amorphous structure, which exhibit high quantum yield and tunable emission from ultraviolet to near-infrared. The growth mechanism and photoluminescence properties of the perovskite amorphous nanoparticles were studied in detail. A high-efficiency green-light-emitting diode based on amorphous CH3NH3PbBr3 nanoparticles was demonstrated. The perovskite amorphous nanoparticle-based light-emitting diode shows a maximum luminous efficiency of 11.49 cd/A, a power efficiency of 7.84 lm/W, and an external quantum efficiency of 3.8%, which is 3.5 times higher than that of the best colloidal perovskite quantum-dot-based light-emitting diodes previously reported. Our findings indicate the great potential of colloidal perovskite amorphous nanoparticles in light-emitting devices.

2Lead-halide perovskites have been attracting attention for potential use in solid-state lighting.Following the footsteps of solar cells, the field of perovskite light-emitting diodes (PeLEDs) has been growing rapidly. Their application prospects in lighting, however, remain still uncertain due to a variety of shortcomings in device performance including their limited levels of luminous efficiency achievable thus far. Here we show high-efficiency PeLEDs based on colloidal perovskite nanocrystals (PeNCs) synthesized at room temperature possessing dominant first-order excitonic radiation (enabling a photoluminescence quantum yield of 71% in solid film), unlike in the case of bulk perovskites with slow electron-hole bimolecular radiative recombination (a second-order process). In these PeLEDs, by reaching charge balance in the recombination zone, we find that the Auger nonradiative recombination, with its significant role in emission quenching, is effectively suppressed in low driving current density range. In consequence, these devices reach a record high maximum external quantum efficiency of 12.9% reported to date and an unprecedentedly high power efficiency of 30.3 lm W -1 at luminance levels above 1000 cd m -2 as required for various applications. These findings suggest that, with feasible levels of device performance, the PeNCs hold great promise for their use in LED lighting and displays.

The performance of a photovoltaic device is strongly dependent on the light harvesting properties of the absorber layer as well as the charge separation at the donor/acceptor interfaces. Atomically thin two-dimensional transition metal dichalcogenides (2-D TMDCs) exhibit strong light-matter interaction, large optical conductivity, and high electron mobility; thus they can be highly promising materials for next-generation ultrathin solar cells and optoelectronics. However, the short optical absorption path inherent in such atomically thin layers limits practical applications. A heterostructure geometry comprising 2-D TMDCs (e.g., MoS2) and a strongly absorbing material with long electron-hole diffusion lengths such as methylammonium lead halide perovskites (CH3NH3PbI3) may overcome this constraint to some extent, provided the charge transfer at the heterostructure interface is not hampered by their band offsets. Herein, we demonstrate that the intrinsic band offset at the CH3NH3PbI3/MoS2 interface can be overcome by creating sulfur vacancies in MoS2 using a mild plasma treatment; ultrafast hole transfer from CH3NH3PbI3 to MoS2 occurs within 320 fs with 83% efficiency following photoexcitation. Importantly, our work highlights the feasibility of applying defect-engineered 2-D TMDCs as charge-extraction layers in perovskite-based optoelectronic devices.

Gold nanostars (GNSs) have received considerable attention in surface-enhanced spectroscopies, catalysis, biosensing, photothermal therapy, and photovoltaics because of their unique optical properties arising from the anisotropic structure. GNSs typically consisting of a central core and several protruding tips are usually synthesized by a seed-mediated growth approach, but the growth mechanism and optical properties have yet to be fully understood. Here, we systematically investigate the seed-mediated growth process of GNSs to gain an insight into the growth mechanism and evolution of their optical and photothermal properties. By tailoring the core size, tip length and tip angle, the main localized surface plasmon resonance (LSPR) peak wavelength can be broadly tuned from the visible to near-infrared (NIR) region. Our observations show that the protruding tips grow rapidly away from the central core at the initial growth stage, leading to a red-shift of the main LSPR peak. The preferential deposition of gold atoms onto the gold core takes place at the later growth stage, gradually blue-shifting the main LSPR peak. GNSs exhibit a large molar extinction coefficient ranging from 4.0 × 10 M cm to 4.5 × 10 M cm, the log value of which correlates linearly with the main LSPR peak wavelength and accordingly allows for facile determination of the GNS concentration in a suspension. In addition, GNSs are excellent NIR photothermal materials with the LSPR-dependent photothermal conversion efficiency. The maximum photothermal conversion efficiency of GNSs occurs at a LSPR wavelength of 740 nm, blue-shifted from the incident laser wavelength. Our present work suggests that GNSs exhibit excellent optical and photothermal properties that can be optimized by tailoring the dimensional parameters.

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