Yijun Xu

Selenium-Doped Black Phosphorus for High-Responsivity 2D Photodetectors

Se-doped black phosphorus (BP) crystal, in centimeter scale, is synthesized by a scalable gas-phase growth method under mild conditions. The Se-doped BP exhibits high quality with excellent electrical properties. The Se dope induces over 20-fold enhancement of responsivity (R) for BP-based 2D photodetectors, resulting in a high R and external quantum efficiency of 15.33 A W-1 and 2993%, respectively.

All-Solid-State High-Energy Asymmetric Supercapacitors Enabled by Three-Dimensional Mixed-Valent MnOx Nanospike and Graphene Electrodes

Three-dimensional (3D) nanostructures enable high-energy storage devices. Here we report a 3D manganese oxide nanospike (NSP) array electrode fabricated by anodization and subsequent electrodeposition. All-solid-state asymmetric supercapacitors were assembled with the 3D Al@Ni@MnOx NSP as the positive electrode, chemically converted graphene (CCG) as the negative electrode, and Na2SO4/poly(vinyl alcohol) (PVA) as the polymer gel electrolyte. Taking advantage of the different potential windows of Al@Ni@MnOx NSP and CCG electrodes, the asymmetric supercapacitor showed an ideal capacitive behavior with a cell voltage up to 1.8 V, capable of lighting up a red LED indicator (nominal voltage of 1.8 V). The device could deliver an energy density of 23.02 W h kg(-1) at a current density of 1 A g(-1). It could also preserve 96.3% of its initial capacitance at a current density of 2 A g(-1) after 10000 charging/discharging cycles. The remarkable performance is attributed to the unique 3D NSP array structure that could play an important role in increasing the effective electrode surface area, facilitating electrolyte permeation, and shortening the electron pathway in the active materials.

Synthesis of three-dimensional hyperbranched TiO2 nanowire arrays with significantly enhanced photoelectrochemical hydrogen production

The three-dimensional (3D) hierarchical nanostructure is one of the promising candidates for high performance photoelectrochemical (PEC) water splitting electrodes due to the reduced carrier diffusion distance, improved light absorption efficiency and charge collection efficiency. Here, by growing omnidirectional, densely packed branches on TiO2 nanowires, we demonstrated a 3D hyperbranched hierarchical TiO2 nanowire (HHNW) architecture that could significantly enhance the performance of PEC water splitting. Under a solar simulator with chopped AM 1.5G light of 100 mW cm−2 intensity, the HHNW electrode yielded a photocurrent density of 1.21 mA cm−2 at 1.23 V with respect to the reversible hydrogen electrode (RHE), which was about four times higher than that of TiO2 nanowires (NWs) (0.34 mA cm−2). The highest incident photon-to-current conversion efficiency (IPCE) obtained from our HHNWs was 77% at 365–425 nm. This greatly improved PEC performance can be attributed to the improved light absorption efficiency and the increased contact surface areas at the TiO2/electrolyte interface.

Few-layer selenium-doped black phosphorus: synthesis, nonlinear optical properties and ultrafast photonics applications

We reported on the synthesis of high quality bulk selenium (Se)-doped black phosphorus (BP) crystals using a mineralizer assisted gas-phase transformation in a mild growth condition and employed a liquid phase exfoliation approach to obtain few-layer (FL) Se-doped BP nano-sheets from the bulk counterpart. We experimentally found that FL Se-doped BP shows enhanced optical saturable absorption with long term stability, which may originate from selenium doping-induced changes of intrinsic carrier density. Taking advantage of its nonlinear optical property, we designed an optical saturable absorber (SA) device based on FL Se-doped BP, allowing the generation of a femto-second pulse in the fiber laser. Our results not only provide a new strategy in tailoring the nonlinear optical response of BP through element doping, but also suggest that FL Se-doped BP can be developed as a excellent candidate for ultrafast photonics.

Interfacial Energy-Level Alignment for High-Performance All-Inorganic Perovskite CsPbBr3 Quantum Dot-Based Inverted Light-Emitting Diodes

All-inorganic perovskite light-emitting diode (PeLED) has a high stability in ambient atmosphere, but it is a big challenge to achieve high performance of the device. Basically, device design, control of energy-level alignment, and reducing the energy barrier between adjacent layers in the architecture of PeLED are important factors to achieve high efficiency. In this study, we report a CsPbBr3-based PeLED with an inverted architecture using lithium-doped TiO2 nanoparticles as the electron transport layer (ETL). The optimal lithium doping balances the charge carrier injection between the hole transport layer and ETL, leading to superior device performance. The device exhibits a current efficiency of 3 cd A-1, a luminance efficiency of 2210 cd m-2, and a low turn-on voltage of 2.3 V. The turn-on voltage is one of the lowest values among reported CsPbBr3-based PeLEDs. A 7-fold increase in device efficiencies has been obtained for lithium-doped TiO2 compared to that for undoped TiO2-based devices.