Pseudohalogen Resurfaced CsPbBr3 Nanocrystals for Bright, Efficient, and Stable Green-Light-Emitting Diodes

Lead halide perovskite nanocrystals (LHP NCs) are regarded as promising emitters for next-generation ultrahigh-definition displays due to their high color purity and wide color gamut. Recently, the external quantum efficiency (EQE) of LHP NC based light-emitting diodes (PNC LEDs) has been rapidly improved to a level required by practical applications. However, the poor operational stability of the device, caused by halide ion migration at the grain boundary of LHP NC thin films, remains a great challenge. Herein, we report a resurfacing strategy via pseudohalogen ions to mitigate detrimental halide ion migration, aiming to stabilize PNC LEDs. We employ a thiocyanate solution processed post-treatment method to efficiently resurface CsPbBr₃ NCs and demonstrate that the thiocyanate ions can effectively inhibit bromide ion migration in LHP NC thin films. Owing to thiocyanate resurfacing, we fabricated LEDs with a high EQE of 17.3%, a maximum brightness of 48000 cd m^-2, and an excellent operation half-life time.

Solution-processed whispering-gallery-mode microsphere lasers based on colloidal CsPbBr3perovskite nanocrystals

Perovskite nanocrystals (NCs) have emerged as attractive gain materials for solution-processed microlasers. Despite the recent surge of reports in this field, it is still challenging to develop low-cost perovskite NC-based microlasers with high performance. Herein, we demonstrate low-threshold, spectrally tunable lasing from ensembles of CsPbBr₃NCs deposited on silica microspheres. Multiple whispering-gallery-mode lasing is achieved from individual NC/microspheres with a low threshold of ∼3.1μJ cm^-2and cavity quality factor of ∼1193. Through time-resolved photoluminescence measurements, electron-hole plasma recombination is elucidated as the lasing mechanism. By tuning the microsphere diameter, the desirable single-mode lasing is successfully achieved. Remarkably, the CsPbBr₃NCs display durable room-temperature lasing under ∼10⁷shots of pulsed laser excitation, substantially exceeding the stability of conventional colloidal NCs. These CsPbBr₃NC-based microlasers can be potentially useful in photonic applications.

Colorimetric sensing of chloride in sweat based on fluorescence wavelength shift via halide exchange of CsPbBr3 perovskite nanocrystals

Considering the high importance of the rapid detection of chloride ion (Cl^-) in sweat for the diagnosis of fibrotic cysts, we have investigated the heterogeneous halide exchange between CsPbBr₃ perovskite nanocrystals (PNCs) in n-hexane and Cl^- in aqueous solution. The results show that CsPbBr₃ PNCs could achieve fast halide exchange with Cl^- in the aqueous phase under magnetic stirring at pH = 1, accompanied by a significant wavelength blue shift and vivid fluorescence color changes from green to blue. Therefore, a fluorescence wavelength shift-based colorimetric sensing of Cl^- based on the halide exchange of CsPbBr₃ PNCs has been developed to realize the rapid detection of Cl^- in sweat. Compared with the conventional fluorescence intensity-based method, this method is of high convenience since the whole procedure could be achieved within 5 min without any sample pretreatment (even no dilution), demonstrating promising application prospects. Graphical Abstract Fluorescence wavelength-shift based colorimetric sensing of chloride in sweat via halide exchange of CsPbBr₃ perovskite nanocrystals.

Composite Films of CsPbBr3 Perovskite Nanocrystals in a Hydrophobic Fluoropolymer for Temperature Imaging in Digital Microfluidics

A composite film material that combines CsPbBr₃ perovskite nanocrystals with a Hyflon AD 60 fluoropolymer was developed and utilized for high-resolution optical temperature imaging. It exhibited bright luminescence and, most importantly, long-term stability in an aqueous medium. CsPbBr₃ nanocrystal-Hyflon films immersed in aqueous solutions showed stable luminescence over at least 4 months and exhibited a fully reversible pronounced temperature sensitivity of 1.2% K^-1 between 20 and 80 °C. They were incorporated into a digital microfluidic (electrowetting on dielectric) platform and were used for spatially resolved temperature measurements during droplet movements. Thermal mapping with a CsPbBr₃ nanocrystal-Hyflon sensing layer in a room temperature environment (22.0 °C) revealed an increase in local temperatures of up to 40.2 °C upon voltage-driven droplet manipulations in a digital microfluidic system, corresponding to a local temperature change of up to 18.2 °C.

Composite Films of CsPbBr3 Perovskite Nanocrystals in a Hydrophobic Fluoropolymer for Temperature Imaging in Digital Microfluidics

A composite film material that combines CsPbBr₃ perovskite nanocrystals with a Hyflon AD 60 fluoropolymer was developed and utilized for high-resolution optical temperature imaging. It exhibited bright luminescence and, most importantly, long-term stability in an aqueous medium. CsPbBr₃ nanocrystal-Hyflon films immersed in aqueous solutions showed stable luminescence over at least 4 months and exhibited a fully reversible pronounced temperature sensitivity of 1.2% K^-1 between 20 and 80 °C. They were incorporated into a digital microfluidic (electrowetting on dielectric) platform and were used for spatially resolved temperature measurements during droplet movements. Thermal mapping with a CsPbBr₃ nanocrystal-Hyflon sensing layer in a room temperature environment (22.0 °C) revealed an increase in local temperatures of up to 40.2 °C upon voltage-driven droplet manipulations in a digital microfluidic system, corresponding to a local temperature change of up to 18.2 °C.

Terahertz Conductivity within Colloidal CsPbBr3 Perovskite Nanocrystals: Remarkably High Carrier Mobilities and Large Diffusion Lengths

Colloidal CsPbBr3 perovskite nanocrystals (NCs) have emerged as an excellent light emitting material in last one year. Using time domain and time-resolved THz spectroscopy and density functional theory based calculations, we establish 3-fold free carrier recombination mechanism, namely, nonradiative Auger, bimolecular electron-hole recombination, and inefficient trap-assisted recombination in 11 nm sized colloidal CsPbBr3 NCs. Our results confirm a negligible influence of surface defects in trapping charge carriers, which in turn results into desirable intrinsic transport properties, from the perspective of device applications, such as remarkably high carrier mobility (∼4500 cm(2) V(-1) s(-1)), large diffusion length (>9.2 μm), and high luminescence quantum yield (80%). Despite being solution processed and possessing a large surface to volume ratio, this combination of high carrier mobility and diffusion length, along with nearly ideal photoluminescence quantum yield, is unique compared to any other colloidal quantum dot system.