Wenxiao Huang

Thickness dependence of the MoO3 blocking layers on ZnO nanorod-inverted organic photovoltaic devices

Organic solar cells based on vertically aligned zinc oxide nanorod arrays (ZNR) in an inverted structure of indium tin oxide (ITO)/ZNR/poly(3-hexylthiophene): (6,6)-phenyl C61 butyric acid methyl ester(P3HT:PCBM)/MoO3/aluminum(Al) were studied. We found that the optimum MoO3 layer thickness condition of 20 nm, the MoO3 can effectively decrease the probability of bimolecular recombination either at the Al interface or within the active layer itself. For this optimum condition we get a power conversion efficiency of 2.15%, a short-circuit current density of 9.02 mA/cm2, an open-circuit voltage of 0.55V, and a fill factor of 0.44 under 100 mW/cm2 irradiation. Our investigations also show that the highly crystallized ZNR can create short and continuous pathways for electron transport and increase the contact area between the ZNR and the organic materials.

Field electron emission of layered Bi2Se3 nanosheets with atom-thick sharp edges

Field electron emission properties of solution processed few-layer Bi₂Se₃ nanosheets are studied for the first time, which exhibit a low turn-on field of 2.3 V μm(-1), a high field enhancement factor of up to 6860 and good field emission stability. This performance is better than that of the as reported layered MoS₂f sheets and is comparable to that of single layer graphene films. The efficient field emission behaviours are found to be not only attributed to their lower work function but also related to their numerous sharp edges or protrusion decorated structure based on our simulation results. Besides, the contribution of possible two-dimensional electron gas surface states of atom-thick layered Bi₂Se₃ nanosheets is discussed in this paper. We anticipate that these solution processed layered Bi₂Se₃ nanosheets have great potential as robust high-performance vertical structure electron emitters for future light weight and highly flexible vacuum micro/nano-electronic device applications.

Effects of electrode modification using calcium on the performance of alternating current field-induced polymer electroluminescent devices

In this work, the effects of electrode modification by calcium (Ca) on the performance of AC field induced polymer electroluminescence (FIPEL) devices are studied. The FIPEL device with Ca/Al electrode exhibits 550 cd m−2, which is 27.5 times higher than that of the device with only an Al electrode (20 cd m−2). Both holes and electrons are injected from one electrode in our FIPEL device. We found that the electron injection can be significantly enhanced by a Ca modification on the Al electrode without greatly affecting the hole injection. Therefore, the electrons and holes can be effectively recombined in the emissive layer to form more excitons under the AC voltage, leading to effective light emission. The device emitted much brighter light than other AC-based organic EL devices. This result provides an easy and effective way to improve FIPEL performance.

Cu2ZnSnSxO4−x and Cu2ZnSnSxSe4−x: First principles simulations of optimal alloy configurations and their energies

With the aim of exploring oxidation and selenization of the photovoltaic material Cu2ZnSnS4, we used first principles methods to study the structure and stability of Cu2ZnSnSxO4−x and Cu2ZnSnSxSe4−x alloys for 0 ≤ x ≤ 4. Pure Cu2ZnSnO4 was found to have the lowest heat of formation, followed by Cu2ZnSnS4, and finally Cu2ZnSnSe4. This suggests that oxidization is very likely to occur, whereas selenization can only be accomplished under high temperature. For the alloys, the energetically favorable chalcogen configurations are very different for oxygen and selenium. While the energies of the selenium alloys are insensitive to the distribution of S and Se configurations, the lowest energy oxygen alloys have alternating S and O sites in the a–b planes. In considering the heats of formation of the Cu2ZnSnSxO4−x alloys, we find that they are unstable with respect to decomposition into binary oxides and sulfides except for small concentrations of O. Our results also show that it is energetically more favorable to...

Imbedded Nanocrystals of CsPbBr3 in Cs4PbBr6: Kinetics, Enhanced Oscillator Strength, and Application in Light-Emitting Diodes

Solution-grown films of CsPbBr3 nanocrystals imbedded in Cs4 PbBr6 are incorporated as the recombination layer in light-emitting diode (LED) structures. The kinetics at high carrier density of pure (extended) CsPbBr3 and the nanoinclusion composite are measured and analyzed, indicating second-order kinetics in extended and mainly first-order kinetics in the confined CsPbBr3 , respectively. Analysis of absorption strength of this all-perovskite, all-inorganic imbedded nanocrystal composite relative to pure CsPbBr3 indicates enhanced oscillator strength consistent with earlier published attribution of the sub-nanosecond exciton radiative lifetime in nanoprecipitates of CsPbBr3 in melt-grown CsBr host crystals and CsPbBr3 evaporated films.

Enhanced stabilization of inorganic cesium lead triiodide (CsPbI3) perovskite quantum dots with tri-octylphosphine

In recent years, significant attention has been paid to perovskite materials. In particular, lead triiodide-based perovskites have exhibited superb optoelectronic properties. Enhancing the stability of these materials is an essential step towards large-scale applications. In this study, by simply adding trioctylphosphine (TOP) as part of the post-synthesis treatment, we significantly enhance the stability of CsPbI3 quantum dots (QDs) in the solution phase, which otherwise decay rapidly in hours. For CsPbI3 QDs treated with TOP, the absorption and photoluminescence emission properties are unchanged over the course of weeks, and the quantum yield remains almost constant at 30% even after 1 month. The morphologies of both treated and untreated QDs are initially cubic; however, the treated QDs largely maintain their initial size and shape, while the untreated ones lose size uniformity, which is a sign of degradation. Infrared spectroscopy and X-ray photoelectron spectroscopy confirm the presence of P in the TOP-treated QDs. We insights that help to resolve the intrinsic instability issue of triiodide perovskite materials and devices.

Solution-processed yellow-white light-emitting diodes based on mixed-solvent dispersed luminescent ZnO nanocrystals

Yellow-white light emitting diodes (LEDs) using ZnO nanocrystals (NCs) as the active materials have been fabricated based on a solution-processed technology. By utilizing a polar-nonpolar mixed-solvent dispersion strategy, uniform dispersion of ZnO NCs with enhanced emission properties has been achieved. The ZnO NCs based LED devices prepared from the mixed-solvent strategy show much improved electroluminescence properties that exhibit a broad yellow-white emission peaks at ∼555 nm with a maximum brightness of 100 cd/m2 and a color rendering index of 77.25. The device mechanism of the LED device was discussed in terms of energy band diagram and current-voltage characteristics.

Wearable Thermoelectric Devices Based on Au-Decorated Two-Dimensional MoS2

Two-dimensional (2D) materials have recently opened a new avenue to flexible thermoelectric materials with enhanced performance because of their unique electronic transport properties. Here, we report a feasible approach to improve the thermoelectric performance of transition-metal dichalcogenides by effectively decorating 2D MoS2 with Au nanoparticles using in situ growth. The present Au-decorated MoS2-assembled heterojunction system shows a certain decoupled phenomenon, that is, the Seebeck coefficient and conductivity increased simultaneously. This is due to the occurrence of p-type doping of the MoS2 2H phase and injection energy filtering of dopant-originated carriers around the local band bending at the interface. The composite flexible films can achieve a power factor value of 166.3 μW m-1 K-2 at room temperature, which have great potential for harvesting human body heat.