Yajing Chang

Shape and phase evolution from CsPbBr3 perovskite nanocubes to tetragonal CsPb2Br5 nanosheets with an indirect bandgap

Tetragonal CsPb2Br5 nanosheets were obtained by an oriented attachment of orthorhombic CsPbBr3 nanocubes, involving a lateral shape evolution from octagonal to square. Meanwhile, the experimental results, together with DFT simulation results, indicated that the tetragonal CsPb2Br5 is an indirect bandgap semiconductor that is PL-inactive with a bandgap of 2.979 eV.

A water–ethanol phase assisted co-precipitation approach toward high quality quantum dot–inorganic salt composites and their application for WLEDs

A green and efficient synthesis of aqueous CdTe quantum dots (QDs) embedded in inorganic salt enabled by co-precipitation is demonstrated, providing a new type of solid-state conversion material with emission colors covering green to red spectral regions. CdTe QDs were synthesized in the water phase, followed by incorporation into inorganic salt with the assistance of ethanol. Due to the protection of the tight matrix, the resulting composites exhibit good stability and processability as well as high photoluminescence properties. A white light emitting diode (WLED) applying the composites as a red color conversion layer with good luminescence properties is also fabricated, suggesting the promising application of the composites in solid-state lighting systems.

Preparation of highly luminescent BaSO4 protected CdTe quantum dots as conversion materials for excellent color-rendering white LEDs

The incorporation of colloidal CdTe quantum dots into an inorganic matrix, BaSO4, through a handy and rapid co-precipitation method is demonstrated for the first time. Owing to the protection of the BaSO4 matrix, the resulting composites show stronger luminescence, longer fluorescent lifetime, and higher photo- and thermal stability as well as being more anti-acid compared to the parental CdTe QDs. Moreover, the composites hold several advantages for industrial applications. White light-emitting diodes (WLEDs) utilizing the composites as a red color conversion layer are fabricated, and produce bright white light with high color-rendering properties including a CIE coordinate of (0.34, 0.33), an Ra of 88, and a Tc of 5112 K at 20 mA, suggesting their great potential application in a solid-state lighting system with high color-rendering properties.

Construction of crossed heterojunctions from p-ZnTe and n-CdSe nanoribbons and their photoresponse properties

Sb-doped p-type ZnTe nanoribbons (NRs) and Ga-doped n-type CdSe NRs were synthesized via a co-thermal evaporation method in a horizontal tube furnace, respectively. Crossbar heterojunction diode (HD) devices were constructed from p-ZnTe:Sb NRs and n-CdSe NRs by a convenient route. The p-ZnTe/n-CdSe NR HD device exhibits a significant rectification characteristic with a rectification ratio up to 103 within ±5 V and a low turn-on voltage of 2.6 V. Photoresponse analysis reveals that such HD devices were highly sensitive to light illumination with excellent stability, reproducibility and fast response speeds of 37/118 μs at reverse bias voltage. It is expected that such HD devices will have great potential applications in electronic and optoelectronic devices in the future.

PbS Quantum-Dot Depleted Heterojunction Solar Cells Employing CdS Nanorod Arrays as the Electron Acceptor with Enhanced Efficiency

Depleted heterojunction (DH) solar cells have shown great potential in power conversion. A 3-D DH structure was first designed and fabricated through a layer-by-layer spin-coating technique to increase the interfacial contact of p-type PbS quantum dots (QDs) and n-type CdS nanorod arrays. As a result, a decent power conversion efficiency of 4.78% in this structure was achieved, which is five times the efficiency of a planar heterojunction structure of a similar thickness. In the 3-D DH structure, n-type CdS nanorod arrays (NRs) were grown vertically as electron acceptors, on which p-type PbS quantum dots were deposited as absorbing materials in a layer-by-layer spin-coating fashion. The results are discussed in view of effective transportation of electrons through CdS NRs than the hopping transportation in large nanoparticle-based CdS film, the enlarged interfacial area, and shortened carrier diffusion distance.

Full-spectra hyperfluorescence cesium lead halide perovskite nanocrystals obtained by efficient halogen anion exchange using zinc halogenide salts

Herein, we demonstrate a facile and less costly approach to deliberately modulate the composition of CsPbX3 (X = Cl, Br, I) NCs. Taking advantage of the highly ionic nature of perovskite structures, complete anion-exchange could be realized on the basis of directly synthesized CsPbBr3 employing zinc halogenide salts as anion source, which embraces the advantages of remarkably short exchange time and room-temperature reaction environment while maintaining the cubic phase for all CsPbX3 NCs, as well as accessing superior perovskite NC qualities with high stability and narrow full width at half maximum peak widths of 18 nm to 38 nm. By controlling the relative concentration of halide anions in a CsPbX3 NC-dispersed solution, their photoluminescence spectra can be finely tuned with ease covering the entire visible spectral region of 410–700 nm.

Ammonium hydroxide modulated synthesis of high-quality fluorescent carbon dots for white LEDs with excellent color rendering properties.

A novel type of aqueous fluorescent carbon dot (CD) was synthesized using citric acid as the only carbon source via an ammonium hydroxide modulated method, providing a blue color gamut. The amino group is considered to be the key factor in the high fluorescence of CDs and a model is established to investigate the mechanism of fluorescence. In addition, white light-emitting diodes (WLEDs) are fabricated by utilizing the prepared CDs and rare earth luminescent materials (SrSi2O2N2:Eu and Sr2Si5N8:Eu) as color conversion layers and UV-LED chips as the excitation light source. The WLEDs produce bright white light with attractive color rendering properties including a color rendering index of up to 95.1, a CIE coordinate of (0.33, 0.37), and a T c of 5447 K under a 100 mA driven current, indicating that the CDs are promising in the field of optoelectronic devices.

High performance visible-near-infrared PbS-quantum-dots/indium Schottky diodes for photodetectors

Here we fabricate self-powered photodetectors based on PbS-quantum-dots/indium Schottky barrier diodes successfully. These devices exhibit excellent repeatability and stability at a high frequency (up to1 MHz), and show a typical fast rise time/fall time of ∼0.8 μs/3.2 μs. They also show excellent rectification ratios up to 104 with bias from -0.5 V to +0.5 V in the dark and a pronounced photovoltaic performance under light illumination. Moreover, the devices demonstrate high sensitivity in weak light illumination detection (detectivity) approaching 1012 Jones and low noise currents <1 pAHz-1/2. These findings suggest great application potential of PbS-quantum-dots for advanced fast response, low noise current, high detectivity and high stability photodetectors.

Interface engineering using a perovskite derivative phase for efficient and stable CsPbBr3 solar cells

Inorganic perovskite materials have great potential for application in optoelectronic devices, especially solar cells, due to their outstanding photoelectric properties and high stability. In this work, we demonstrated CsPbBr3 inorganic perovskite solar cells (PSCs) composed of a derivative-phase CsPb2Br5 for the first time by precisely controlling the film thickness of precursor materials. The presence of CsPb2Br5 at the interface of CsPbBr3 crystals can increase the grain size of the inorganic perovskite and effectively passivate grain defects and the electron transport layer. The derivative phase will lower the energy barrier and reduce the carrier recombination in the active layer. Remarkably, this self-passivation results in a respectable power conversion efficiency (PCE) of 8.34% with a CsBr : PbBr2 ratio of 1 : 1.1. Besides, the device exhibits a superior stability for more than 1000 h without any degradation. Insights into the derivative phase formation and self-passivation mechanisms are demonstrated, providing a novel approach to improve the performance of perovskite solar cells.

All-Inorganic Perovskite Nanocrystals with a Stellar Set of Stabilities and Their Use in White Light-Emitting Diodes

We report a simple, robust, and inexpensive strategy to enable all-inorganic CsPbX3 perovskite nanocrystals (NCs) with a set of markedly improved stabilities, that is, water stability, compositional stability, phase stability, and phase segregation stability via impregnating them in solid organic salt matrices (i.e., metal stearate; MSt). In addition to acting as matrices, MSt also functions as the ligand bound to the surface of CsPbX3 NCs, thereby eliminating the potential damage of NCs commonly encountered during purification as in copious past work. Quite intriguingly, the resulting CsPbX3-MSt nanocomposites display an outstanding suite of stabilities. First, they retain high emission in the presence of water because of the insolubility of MSt in water, signifying their excellent water stability. Second, anion exchange between CsPbBr3-MSt and CsPbI3-MSt nanocomposites is greatly suppressed. This can be ascribed to the efficient coating of MSt, thus effectively isolating the contact between CsPbBr3 and CsPbI3 NCs, reflecting notable compositional stability. Third, remarkably, after being impregnated by MSt, the resulting CsPbI3-MSt nanocomposites sustain the cubic phase of CsPbI3 and high emission, manifesting the strikingly improved phase stability. Finally, phase segregation of CsPbBr1.5I1.5 NCs is arrested via the MSt encapsulation (i.e., no formation of the respective CsPbBr3 and CsPbI3), thus rendering pure and stable photoluminescence (i.e., demonstration of phase segregation stability). Notably, when assembled into typical white light-emitting diode architecture, CsPbBr1.5I1.5-MSt nanocomposites exhibit appealing performance, including a high color rendering index ( Ra) and a low color temperature ( Tc). As such, the judicious encapsulation of perovskite NCs into organic salts represents a facile and robust strategy for creating high-quality solid-state luminophores for use in optoelectronic devices.