Guopeng Li

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.

Crystallographic-plane tuned Prussian-blue wrapped with RGO: a high-capacity, long-life cathode for sodium-ion batteries

Designing Prussian blue with optimally exposed crystal planes and confining it in a conductive matrix are critical issues for improving its sodium storage performance, and will result in much improved sodium ion adsorption and diffusion, together with improved electron mobility. Here, we firstly illustrate through DFT simulations that the {100} lattice planes and [100] direction of the KxFeFe(CN)6 crystal are the preferred occupation sites and diffusion route for sodium ions. In addition, through coupling with RGO, KxFeFe(CN)6 electrodes exhibit better electronic conductivity. Accordingly, {100} plane-capped cubic K0.33FeFe(CN)6 wrapped in RGO was fabricated using a facile CTAB-assisted method. Due to the highly robust framework, higher specific surface area, greatly reduced number of lattice water defects and conductive RGO coating, K0.33FeFe(CN)6/RGO exhibits superior electrochemical performance in sodium-ion batteries. As a cathode, the RGO-coated K0.33FeFe(CN)6 yields an initial discharge–charge capacity of 160 mA h g−1 at a rate of 0.5C, and an excellent capacity retention of 92.2% at 0.5C and 90.1% at 10C after 1000 and 500 cycles. Furthermore, XRD, DFT simulation, XANES and EXAFS verified that the structural changes during the Na-ion insertion–extraction processes are highly reversible. All these results suggest that {100} plane-capped K0.33FeFe(CN)6/RGO has excellent potential as a cathode for sodium-ion batteries.

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.

Dual‐Phase CsPbBr3–CsPb2Br5 Perovskite Thin Films via Vapor Deposition for High‐Performance Rigid and Flexible Photodetectors

Inorganic perovskites with special semiconducting properties and structures have attracted great attention and are regarded as next generation candidates for optoelectronic devices. Herein, using a physical vapor deposition process with a controlled excess of PbBr2 , dual-phase all-inorganic perovskite composite CsPbBr3 -CsPb2 Br5 thin films are prepared as light-harvesting layers and incorporated in a photodetector (PD). The PD has a high responsivity and detectivity of 0.375 A W-1 and 1011 Jones, respectively, and a fast response time (from 10% to 90% of the maximum photocurrent) of ≈280 µs/640 µs. The device also shows an excellent stability in air for more than 65 d without encapsulation. Tetragonal CsPb2 Br5 provides satisfactory passivation to reduce the recombination of the charge carriers, and with its lower free energy, it enhances the stability of the inorganic perovskite devices. Remarkably, the same inorganic perovskite photodetector is also highly flexible and exhibits an exceptional bending performance (>1000 cycles). These results highlight the great potential of dual-phase inorganic perovskite films in the development of optoelectronic devices, especially for flexible device applications.

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.

Three-dimensional architecture hybrid perovskite solar cells using CdS nanorod arrays as an electron transport layer

Three-dimensional (3D) architecture perovskite solar cells (PSCs) using CdS nanorod (NR) arrays as an electron transport layer were designed and prepared layer-by-layer via a physical-chemical vapor deposition (P-CVD) process. The CdS NRs not only provided a scaffold to the perovskite film, but also increased the interfacial contact between the perovskite film and electron transport layer. As an optimized result, a high power conversion efficiency of 12.46% with a short-circuit current density of 19.88 mA cm-2, an open-circuit voltage of 1.01 V and a fill factor of 62.06% was obtained after 12 h growth of CdS NRs. It was four times the efficiency of contrast planar structure with a similar thickness. The P-CVD method assisted in achieving flat and voidless CH3NH3PbI3-x Cl x perovskite film and binding the CdS NRs and perovskite film together. The different density of CdS NRs had obvious effects on light transmittance of 350-550 nm, the interfacial area and the difficulty of combining layers. Moreover, the efficient 1D transport paths for electrons and multiple absorption of light, which are generated in 3D architecture, were beneficial to realize a decent power conversion efficiency.