Chaochao Dun

Layered Bi2Se3 Nanoplate/Polyvinylidene Fluoride Composite Based n-type Thermoelectric Fabrics

In this study, we report the fabrication of n-type flexible thermoelectric fabrics using layered Bi2Se3 nanoplate/polyvinylidene fluoride (PVDF) composites as the thermoelectric material. These composites exhibit room temperature Seebeck coefficient and electrical conductivity values of -80 μV K(-1) and 5100 S m(-1), respectively, resulting in a power factor approaching 30 μW m(-1)K(-2). The temperature-dependent thermoelectric properties reveal that the composites exhibit metallic-like electrical conductivity, whereas the thermoelectric power is characterized by a heterogeneous model. These composites have the potential to be used in atypical applications for thermoelectrics, where lightweight and flexible materials would be beneficial. Indeed, bending tests revealed excellent durability of the thermoelectric fabrics. We anticipate that this work may guide the way for fabricating high performance thermoelectric fabrics based on layered V-VI nanoplates.

Nanowires as Building Blocks to Fabricate Flexible Thermoelectric Fabric: The Case of Copper Telluride Nanowires

A general approach to fabricate nanowires based inorganic/organic composite flexible thermoelectric fabric using a simple and efficacious five-step vacuum filtration process is proposed. As an excellent example, the performance of freestanding flexible thermoelectric thin film using copper telluride nanowires/polyvinylidene fluoride (Cu1.75Te NWs/PVDF = 2:1) as building block is demonstrated. By burying the Cu1.75Te NWs into the PVDF polymer agent, the flexible fabric exhibits room-temperature Seebeck coefficient and electric conductivity of 9.6 μV/K and 2490 S/cm, respectively, resulting in a power factor of 23 μW/(mK(2)) that is comparable to the bulk counterpart. Furthermore, this NW-based flexible fabric can endure hundreds of cycles of bending tests without significant performance degradation.

Colloidal Cobalt Phosphide Nanocrystals as Trifunctional Electrocatalysts for Overall Water Splitting Powered by a Zinc–Air Battery

Highly efficient and stable electrocatalysts, particularly those that are capable of multifunctionality in the same electrolyte, are in high demand for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). In this work, highly monodisperse CoP and Co2 P nanocrystals (NCs) are synthesized using a robust solution-phase method. The highly exposed (211) crystal plane and abundant surface phosphide atoms make the CoP NCs efficient catalysts toward ORR and HER, while metal-rich Co2 P NCs show higher OER performance owing to easier formation of plentiful Co2 P@COOH heterojunctions. Density functional theory calculation results indicate that the desorption of OH* from cobalt sites is the rate-limiting step for both CoP and Co2 P in ORR and that the high content of phosphide can lower the reaction barrier. A water electrolyzer constructed with a CoP NC cathode and a Co2 P NC anode can achieve a current density of 10 mA cm-2 at 1.56 V, comparable even to the noble metal-based Pt/C and RuO2 /C pair. Furthermore, the CoP NCs are employed as an air cathode in a primary zinc-air battery, exhibiting a high power density of 62 mW cm-2 and good stability.

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...

Environmentally benign synthesis of high-quality, band gap-tunable, homogeneous Te/Se alloyed nanowires

Ultrathin trigonal Te/Se alloyed nanowires with a tunable composition and band gap were fabricated using a nonhazardous reducing agent, ascorbic acid. The as-synthesized nanowires displayed a tunable direct band gap (3.39 to 3.78 eV) and indirect band gap (1.99 eV to 2.93 eV).

Solution-based synthesis and processing of Sn- and Bi-doped Cu3SbSe4 nanocrystals, nanomaterials and ring-shaped thermoelectric generators

Copper-based chalcogenides that comprise abundant, low-cost, and environmental friendly elements are excellent materials for a number of energy conversion applications, including photovoltaics, photocatalysis, and thermoelectrics (TE). In such applications, the use of solution-processed nanocrystals (NCs) to produce thin films or bulk nanomaterials has associated several potential advantages, such as high material yield and throughput, and composition control with unmatched spatial resolution and cost. Here we report on the production of Cu3SbSe4 (CASe) NCs with tuned amounts of Sn and Bi dopants. After proper ligand removal, as monitored by nuclear magnetic resonance and infrared spectroscopy, these NCs were used to produce dense CASe bulk nanomaterials for solid state TE energy conversion. By adjusting the amount of extrinsic dopants, dimensionless TE figures of merit (ZT) up to 1.26 at 673 K were reached. Such high ZT values are related to an optimized carrier concentration by Sn doping, a minimized lattice thermal conductivity due to efficient phonon scattering at point defects and grain boundaries, and to an increase of the Seebeck coefficient obtained by a modification of the electronic band structure with Bi doping. Nanomaterials were further employed to fabricate ring-shaped TE generators to be coupled to hot pipes, which provided 20 mV and 1 mW per TE element when exposed to a 160 °C temperature gradient. The simple design and good thermal contact associated with the ring geometry and the potential low cost of the material solution processing may allow the fabrication of TE generators with short payback times.

Achieving High Performance in AC-Field Driven Organic Light Sources.

Charge balance in organic light emitting structures is essential to simultaneously achieving high brightness and high efficiency. In DC-driven organic light emitting devices (OLEDs), this is relatively straight forward. However, in the newly emerging, capacitive, field-activated AC-driven organic devices, charge balance can be a challenge. In this work we introduce the concept of gating the compensation charge in AC-driven organic devices and demonstrate that this can result in exceptional increases in device performance. To do this we replace the insulator layer in a typical field-activated organic light emitting device with a nanostructured, wide band gap semiconductor layer. This layer acts as a gate between the emitter layer and the voltage contact. Time resolved device characterization shows that, at high-frequencies (over 40 kHz), the semiconductor layer allows for charge accumulation in the forward bias, light generating part of the AC cycle and charge compensation in the negative, quiescent part of the AC cycle. Such gated AC organic devices can achieve a non-output coupled luminance of 25,900 cd/m2 with power efficiencies that exceed both the insulator-based AC devices and OLEDs using the same emitters. This work clearly demonstrates that by realizing balanced management of charge, AC-driven organic light emitting devices may well be able to rival today’s OLEDs in performance.

Correlation of atomic packing with the boson peak in amorphous alloys

Boson peaks (BP) have been observed from phonon specific heats in 10 studied amorphous alloys. Two Einstein-type vibration modes were proposed in this work and all data can be fitted well. By measuring and analyzing local atomic structures of studied amorphous alloys and 56 reported amorphous alloys, it is found that (a) the BP originates from local harmonic vibration modes associated with the lengths of short-range order (SRO) and medium-range order (MRO) in amorphous alloys, and (b) the atomic packing in amorphous alloys follows a universal scaling law, i.e., the ratios of SRO and MRO lengths to solvent atomic diameter are 3 and 7, respectively, which exact match with length ratios of BP vibration frequencies to Debye frequency for the studied amorphous alloys. This finding provides a new perspective for atomic packing in amorphous materials, and has significant implications for quantitative description of the local atomic orders and understanding the structure-property relationship.

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.