Xiaosheng Tang

Femtosecond laser direct writing of microholes on roughened ZnO for output power enhancement of InGaN light-emitting diodes.

A significant enhancement of light extraction efficiency from InGaN light-emitting diodes (LEDs) with microhole arrays and roughened ZnO was experimentally demonstrated. The roughened ZnO was fabricated using an Ar and H2 plasma treatment of ZnO films pre-coated on a p-GaN layer. When followed by a femtosecond laser direct writing technique, a periodic array of microholes could be added to the surface. The diameter of the microhole was varied by changing the output power of the femtosecond laser. Compared to conventional LEDs on the same wafer, the output power of LEDs with roughened ZnOs and a microhole (diameter of 2 μm) array was increased by 58.4% when operated with an injection current of 220 mA. Moreover, it was found that LEDs fabricated with roughened ZnO and the microhole array had similar current-voltage (I-V) characteristics to those of conventional LEDs and no degrading effect was observed.

Synthesis of MoS 2 /g-C 3 N 4 nanocomposites with enhanced visible-light photocatalytic activity for the removal of nitric oxide (NO)

Molybdenum disulfide and graphitic carbon nitride (MoS₂-g-C₃N₄) nanocomposites with visible-light induced photocatalytic activity were successfully synthesized by a facile ultrasonic dispersion method. The crystalline structure and morphology of the MoS₂-g-C₃N₄ nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microcopy (TEM), high-resolution TEM (HRTEM) and scanning electron microscopy (SEM). The optical property of the as-prepared nanocomposites was studied by ultraviolet visible diffusion reflection (UV-vis) and photoluminescence(PL) spectrum. It could be observed from the TEM image that the MoS₂ nanosheets and g-C₃N₄ nanoparticles were well combined together. Moreover, the photocatalytic activity of MoS₂-g-C₃N₄ composites was evaluated by the removal of nitric oxide under visible light irradiation (>400nm). The experimental results demonstrated that the nanocomposites with the MoS₂ content of 1.5 wt% exhibited optimal photocatalytic activity and the corresponding removal rate of NO achieved 51.67%, higher than that of pure g-C₃N₄ nanoparticles. A possible photocatalytic mechanism for the MoS₂-g-C₃N₄ nanocomposites with enhanced photocatalytic activity could be ascribed to the hetero-structure of MoS₂ and g-C₃N₄.

Performance improvement of perovskite solar cells by employing a CdSe quantum dot/PCBM composite as an electron transport layer

Organic–inorganic hybrid perovskites have recently attracted considerable interest for application in solar cells due to their low cost, high absorption coefficient and high power conversion efficiency (PCE). Herein, we utilize a CdSe quantum dot/PCBM composite as an electron transport layer (ETL) to investigate the structure, stability and PCE of CH3NH3PbI3−xClx perovskite solar cells. It is found that adsorption of the CdSe/PCBM composite reduces the roughness of the perovskite, leading to a high-quality film with a compact morphology. Density functional theory (DFT) based first-principles calculations show that CdSe enhances the chemical stability of CH3NH3PbI3−xClx involving strong atomic orbital hybridization. Interestingly, an inorganic-terminated perovskite surface has much stronger interaction with CdSe compared to the surface with organic CH3NH3 termination, with noticeable interfacial charge redistribution. Experiments on solar cells incorporating the CdSe/PCBM composite as the ETL show enhanced photocurrent and fill factor, which is related to the in-built electric field between CH3NH3PbI3−xClx and CdSe that greatly facilitates the separation of electron and hole pairs. We show an improved PCE of 13.7% with enhanced device stability in a highly humid atmosphere. These joint theoretical–experimental results may provide a new aspect for improving the structural stability and operating performance of optoelectronic devices based on perovskite structures.

Flexible All-Inorganic Perovskite CsPbBr3 Nonvolatile Memory Device

All-inorganic perovskite CsPbX3 (X = Cl, Br, or I) is widely used in a variety of photoelectric devices such as solar cells, light-emitting diodes, lasers, and photodetectors. However, studies to understand the flexible CsPbX3 electrical application are relatively scarce, mainly due to the limitations of the low-temperature fabricating process. In this study, all-inorganic perovskite CsPbBr3 films were successfully fabricated at 75 °C through a two-step method. The highly crystallized films were first employed as a resistive switching layer in the Al/CsPbBr3/PEDOT:PSS/ITO/PET structure for flexible nonvolatile memory application. The resistive switching operations and endurance performance demonstrated the as-prepared flexible resistive random access memory devices possess reproducible and reliable memory characteristics. Electrical reliability and mechanical stability of the nonvolatile device were further tested by the robust current-voltage curves under different bending angles and consecutive flexing cycles. Moreover, a model of the formation and rupture of filaments through the CsPbBr3 layer was proposed to explain the resistive switching effect. It is believed that this study will offer a new setting to understand and design all-inorganic perovskite materials for future stable flexible electronic devices.

Enhanced Stability and Tunable Photoluminescence in Perovskite CsPbX3/ZnS Quantum Dot Heterostructure

All-inorganic perovskite CsPbX3 (X = Cl, Br, I) and related materials are promising candidates for potential solar cells, light emitting diodes, and photodetectors. Here, a novel architecture made of CsPbX3 /ZnS quantum dot heterodimers synthesized via a facile solution-phase process is reported. Microscopic measurements show that CsPbX3 /ZnS heterodimer has high crystalline quality with enhanced chemical stability, as also evidenced by systematic density functional theory based first-principles calculations. Remarkably, depending on the interface structure, ZnS induces either n-type or p-type doping in CsPbX3 and both type-I and type-II heterojunctions can be achieved, leading to rich electronic properties. Photoluminescence measurement results show a strong blue-shift and decrease of recombination lifetime with increasing sulfurization, which is beneficial for charge diffusion in solar cells and photovoltaic applications. These findings are expected to shed light on further understanding and design of novel perovskite heterostructures for stable, tunable optoelectronic devices.

Inverted Planar Perovskite Solar Cells with a High Fill Factor and Negligible Hysteresis by the Dual Effect of NaCl-Doped PEDOT:PSS

The performance of inverted perovskite solar cells is highly dependent on hole extraction and surface properties of hole transport layers. To highlight the important role of hole transport layers, a facile and simple method is developed by adding sodium chloride (NaCl) into poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The average power conversion efficiency of the perovskite solar cells prepared on NaCl-doped PEDOT:PSS is 17.1% with negligible hysteresis, compared favorably to the control devices (15.1%). Particularly, they exhibit markedly improved Voc and fill factor (FF), with the best FF as high as 81.9%. The enhancement of photovoltaic performance is ascribed to two effects. Better conductivity and hole extraction of PEDOT:PSS are observed after NaCl doping. More intriguingly, the perovskite polycrystalline film shows a preferred orientation along the (001) direction on NaCl-doped PEDOT:PSS, leading to a more uniform thin film. The comparison of the crystal structure between NaCl and MAPbCl3 indicates a lattice constant mismatch less than 2% and a matched chlorine atom arrangement on the (001) surface, which implies that the NaCl crystallites on the top surface of PEDOT:PSS might serve as seeds guiding the growth of perovskite crystals. This simple method is fully compatible with printing technologies to mass-produce perovskite solar cells with high efficiency and tunable crystal orientations.

Robust Subwavelength Single-Mode Perovskite Nanocuboid Laser

On-chip photonic information processing systems require great research efforts toward miniaturization of the optical components. However, when approaching the classical diffraction limit, conventional dielectric lasers with all dimensions in nanoscale are difficult to realize due to the ultimate miniaturization limit of the cavity length and the extremely high requirement of optical gain to overcome the cavity loss. Herein, we have succeeded in reducing the laser size to subwavelength scale in three dimensions using an individual CsPbBr3 perovskite nanocuboid. Even though the side length of the nanocuboid laser is only ∼400 nm, single-mode Fabry-Pérot lasing at room temperature with laser thresholds of 40.2 and 374 μJ/cm2 for one- and two-photon excitation has been achieved, respectively, with the corresponding quality factors of 2075 and 1859. In addition, temperature-insensitive properties from 180 to 380 K have been demonstrated. The physical volume of a CsPbBr3 nanocuboid laser is only ∼0.49λ3 (where λ is the lasing wavelength in air). Its three-dimensional subwavelength size, excellent stable lasing performance at room temperature, frequency up-conversion ability, and temperature-insensitive properties may lead to a miniaturized platform for nanolasers and integrated on-chip photonic devices in nanoscale.

Transient multiexponential signals analysis using Bayesian deconvolution

A new method based on Bayesian deconvolution is proposed for multiexponential transient signal analysis. The multiexponential signal is initially converted to a convolution model using logarithmic and differential transformation after which the Bayesian iteration is used to deconvolve the data. The numerical simulation is applied on four different multiexponential signals with different levels of noise. Thermal transient experiment data of the high power light emitting diodes are also analyzed using the proposed method. Simulation and experimental results indicate that the present method performs efficiently in accurately estimating the decay rates except at low SNR case.

All-inorganic CsPbBr3 perovskite quantum dots as a photoluminescent probe for ultrasensitive Cu2+ detection

Pollution triggered by highly toxic heavy metal ions has become a worldwide issue of concern, and has aroused increasing research interest, but it is still a challenge to carry out its trace detection in the organic phase using inorganic fluorescent colloidal nanocrystals (NCs). Herein, we report fully inorganic CsPbBr3 perovskite quantum dots (PQDs), which were synthesized via a hot-injection method, as a fluorescent probe for the selective detection of copper ions in hexane. The photoluminescence (PL) intensity of CsPbBr3 PQDs is significantly quenched within several seconds after the addition of Cu2+ due to effective electron transfer from the PQDs to the added Cu2+, which is experimentally verified via analyzing absorption spectra and PL decay lifetime. The sensor, in turn-off mode, has a detection range from 0 to 100 nM with a limit of detection (LOD) as low as 0.1 nM, indicating great potential for practical applications. This study paves the way for PQD-based fluorescent probes for heavy metal detection in the organic phase.

A high-sensitivity zero-biased magnetoelectric sensor using five-phase laminate composites based on FeCoV nanocrystalline soft magnetic alloy

This paper present a high-sensitivity zero-biased ME sensor consists of FeCoV/Terfenol-D/Pb(Zr1-x,Tix)O3(PZT)/Terfenol-D/FeCoV (FMPMF), whose magnetoelectric (ME) coupling characteristics and ME sensing performance have been investigated. Compared to traditional Terfenol-D/PZT/Terfenol-D (MPM) sensor, the zero-biased ME coupling characteristics of FMPMF sensor were significantly improved. Meanwhile, the induced zero-biased ME voltage of FMPMF sensor shows an excellent linear relationship to ac magnetic field both at the low frequency (1kHz) and the resonant frequency (115.14 kHz). The measured sensitivity at resonance is 1.95 V/Oe and the output resolution is approximately 2.43×10-8T. The proposed FMPMF sensors still have very good performance in the current sensing. The measured results shows an average sensitivity of 1.14 mV/A with highly linear behavior in the current range 1 A to 10 A at 50 Hz. Remarkably, it indicates that the proposed zero-biased miniature ME sensor give the prospect of being able t...