A solution-processable D–A–D small molecule based on isoindigo for organic solar cells

A new linear D–A–D organic small molecule (M1), with triphenylamine as electron donor (D) unit and isoindigo (ID) as electron acceptor (A) unit, was synthesized by Stille coupling reactions. It exhibits broad and strong absorption (300–700 nm), a relatively low HOMO energy level (?5.30 eV), low band gap (1.69 eV), and moderate hole mobility (2.49×10^?4 cm²/Vs). Solution-processed small molecule bulk-heterojunction solar cells based on M1: PC₆₁BM (1:3, w/w) blend film exhibits a power conversion efficiency of 0.84 % with an open-circuit voltage (V _oc) of 0.78 V, under the illumination of AM1.5, 100 mW/cm².     

Synthesis and characterization of novel D–A porphyrin-containing copolymers for polymer solar cells

A novel asymmetrical D–A zinc porphyrin derivative with dimehtyl triphenylamine (donor unit) and methyl benzoate (acceptor unit) as para-arms was first synthesized. Then, two new copolymers (P1 and P2) containing D–A zinc porphyrin derivatives were synthesized by the Stille coupling method and applied in PSCs. Their structures, photophysical and electrochemical properties were characterized by ¹H NMR, ¹³C NMR, gel permeation chromatography, thermogravimetric analysis, UV–vis absorption spectroscopy, photoluminescence spectroscopy, and cyclic voltammetry. The two copolymers exhibited good thermal stability and film-forming ability. The results showed that P1 containing D–A zinc porphyrin exhibits a strong absorption in the range of 400–500 nm. By the introduction of thiophene derivative with 4,7-di(4-hexylthiophen-2-yl)benzothiadiazole (T-DTBT) conjugated side-chain unit, P2 showed broader absorption in the region of 300–650 nm than P1. The photoluminescence spectra made clear that charge transfer between the whole main chain and side chain can be effective. Cyclic voltammograms revealed that the LUMO energy levels of P2 was reduced in comparison with P1 due to the introduction of electron-deficient T-DTBT conjugated side-chain unit, indicating that electron-injection and transporting properties have been improved. Polymer solar cells were fabricated based on the blend of the copolymers and methanofullerene[6,6]-phenyl C₆₁-butyric acid methyl ester (PC₆₁BM). The PSC based on P2:PC₆₁BM (1:2, w/w) exhibited a power conversion efficiency of 1.26% under AM 1.5, 100 mW cm⁻².     

Novel hybrid solar cells based on α-copper phthalocyanine–cadmium sulfide planar heterojunction

Cadmium sulfide (CdS) has been employed as an alternative acceptor for planar heterojunction solar cell based on copper phthalocyanine (CuPc). Spin-coated poly-3,4-ethylenedioxythiophene:polystyrenesulfonate (PEDOT:PSS) on indium tin oxide (ITO)-coated glass substrates was used for the vacuum deposition of CuPc and CdS planar heterojunction. In the present study, we have fabricated two different architectures of CuPc/CdS devices: (1) ITO/PEDOT:PSS/CuPc/CdS/Al and (2) ITO/PEDOT:PSS/CuPc/CdS/LiF/Al. Our results indicate that the CdS could effectively facilitate charge transport in the nanostructured network, and be a good acceptor. The fabricated bare CuPc/CdS device shows 0.13 % conversion efficiency while incorporation of LiF layer between CuPc/CdS and Al contact facilitates low-recombination rate results ~43 % enhancement in efficiency. The ITO/PEDOT:PSS/CuPc/CdS/LiF/Al device shows 0.30 % power conversion efficiency.     

Synthesis and characterization of Y-shape electron donor–acceptor type organic dyes for dye-sensitized solar cells

Three Y-shape organic dyes, (Z)-3-(5-(3,5-bis(4-(9H-carbazol-9-yl)styryl)-4-methoxyphenyl)thiophen-2-yl)-2-cyanoacrylic acid (OD-1), (Z)-3-(5′-(3,5-bis(4-(9H-carbazol-9-yl)styryl)-4-methoxyphenyl)-2,2′-bithiophen-5-yl)-2-cyanoacrylic acid (OD-2) and (Z)-3-(5′-(3,5-bis(4-(9H-carbazol-9-yl)styryl)-4-methoxyphenyl)-3,4′-4″-trithiophenyl-5-yl)-2-cyanoacrylic acid (OD-3) were synthesized and used as sensitizers in nanocrystalline dye-sensitized solar cells (DSSCs). The introduction of the bis(carbazolylstyryl) units as an electron donor group and oligothiophene units as a both electron donors and π-spacers increased the conjugation length of the sensitizers and thus improved their molar absorption coefficient and light harvesting efficiency. DSSCs with the configuration of SnO₂:F/TiO₂/organic dye/liquid electrolyte/Pt devices were fabricated using these OD-1, OD-2 and OD-3 as a sensitizers. Among the devices, the DSSC composed of OD-3 exhibited highest power conversion efficiency of 3.03% under AM1.5G (100 mW cm⁻²).     

Simple indoline based donor–acceptor dye for high efficiency dye-sensitized solar cells

A simple metal-free donor–acceptor type sensitizer U01, bearing strong electron donor indoline-triphenylamine was synthesized for panchromatic sensitization of TiO₂ nanocrystalline film. Photovoltaic properties of U01 showed remarkably enhanced light harvesting due to the presence of strong electron donor and robust structure. The new U01 sensitized solar cell exhibited a photovoltaic performance: a short-circuit photocurrent density (J_sc) of 10.70 mA cm⁻², an open-circuit photovoltage (V_oc) of 0.758 V and a fill factor (FF) of 0.74, corresponding to an overall conversion efficiency of 6.01% under standard global AM 1.5 solar light condition. Our results suggest that indoline-triphenylamine based robust D–A molecular architecture is a highly promising class of panchromatic sensitizers for improvement of the performance of dye-sensitized solar cells (DSCs).     

Influence of position of auxiliary acceptor in D–A–π–A photosensitizes on photovoltaic performances of dye-sensitized solar cells

Several novel indoline dyes configured with donor–acceptor–bridge–acceptor (D–A–π–A) structures were designed and applied to organic dye-sensitized solar cells. These D–A–π–A dye molecules are composed of indoline (electron donating group), benzothiadiazole (BDT) (auxiliary acceptor), two furan rings (π-conjugated group), and 2-cyanoacrylic acid (electron accepting group). The influence of position of auxiliary acceptor in D–A–π–A organic sensitizer on the performance of photosensitize is investigated in detail. Calculated results show that the sensitizer could achieve a red-shifted absorption in long-wavelength region and a stronger absorption in short-wavelength region when the position of auxiliary acceptor changes from the donor to the acceptor. Moreover, among these dyes, WS-12, whose auxiliary acceptor nearing the 2-cyanoacrylic acid, possesses the better performance in terms of the charge transfer characteristics, lifetime of excited state as well as the vertical dipole moment when compared with WS-1 and WS-11. We hope that the present results could provide theoretical guidance for designing photosensitizes with higher efficiencies.     

Rational design and characterization of high-efficiency planar A–π–D–π–A type electron donors in small molecule organic solar cells: A quantum chemical approach

Taking the reported donor DR3TBDT as reference, a series of A–π–D–π–A type donor molecules involving different planar donor cores were designed and investigated by using density functional theory (DFT)/time-dependent DFT methods. Preliminary calculations on geometries, energy levels and spectrum properties show that four of the designed molecules (4, 5, 12 and 13) could become potential donor replacements of DR3TBDT due to their good planarity, larger light harvesting efficiencies and similar exciton migration capability. Additionally, several factors influencing on short-circuit current density (J_sc) were analyzed by in-depth quantum chemical investigations on the transition density matrix, charge transfer indexes, exciton binding energy and Gibbs free energy loss in charge dissociation process. Comparative analyses demonstrate that 4 with indaceno[1,2-b:5,6-b′]dithiophene donor core has more significant electron transfer character and favorable exciton dissociation capability for enhancing the J_sc, and would be potentially promising donor material in organic solar cells.     

Current transport mechanism of heterojunction diodes based on the sol–gel p-type ZnO and n-type Si with H2O2 treatment

The present work reports the fabrication and detailed electrical properties of heterojunction diodes based on the sol–gel p-type ZnO and n-type Si. The p-type ZnO/n-type Si diode without H₂O₂ treatment showed a poor rectifying behavior with an ideality factor (n) of 6.4 and high leakage. n > 2 implies that the interfacial defects influence the electronic conduction through the device. However, the p-type ZnO/n-type Si diode with H₂O₂ treatment showed a good rectifying behavior with n of 1.6 and low leakage. Such an improvement indicates that a good passivation is formed at the interface as a result of the reduction of the defect density. These experimental demonstrations suggest that it may be possible to minimize the adverse effects of the interface states to obtain functional devices using H₂O₂ treatment.     

Dye-sensitized solar cells based on composite TiO<Subscript>2</Subscript> nanoparticle–nanorod single and bi-layer photoelectrodes

TiO₂ nanoparticle (NP), composite TiO₂ nanoparticle–nanorod (NP–NR) and bi-layer TiO₂ nanoparticle/nanorod (NP/NR) with the optimized diameter of NRs had been prepared as anode layer in dye-sensitized solar cells (DSSCs). Morphology and thickness of anode layers were provided by field emission scanning electron microscope (FE-SEM) and scanning electron microscopy (SEM) devices. Current density–voltage diagrams were prepared by potentiostat and solar simulator devices at air mass (AM) 1.5. It is determined that DSSCs based on composite NP–NR photoelectrode had the best conversion efficiency of 5.07%. Also, the results of the electrochemical modelling of these DSSCs indicated that solar cells based on NP–NR electrode had the highest electron transport time (τ _d) of 312.87 ms, electrons’ recombination lifetime (τ _n) of 130.4 ms and the lowest transfer resistance (R _ct) as well as transport resistance (R _t) of 22.46 and 9.4 Ω, respectively.     

Formulated quasi-solid state electrolyte based on polypyrrole/polyaniline–polyurethane nanocomposite for dye-sensitized solar cell

A polymer-based quasi-solid state electrolyte using polyurethane (PU) matrix was applied for dye-sensitized solar cell (DSSC). To further improve the performance of the electrolyte, 10 wt% of conductive polymer [polypyrrole (PPy) and polyaniline (PANi)] nanoparticles were introduced into the matrix. The samples were named PU-10%PPy and PU-10%PANi, and characterized using ATR–FTIR, TEM, DLS, a transmitted light microscope, a reflected light microscope, and TGA. The formulated polymeric nanocomposites were immersed in the liquid electrolyte and the polymer matrix absorbency, conductivity (σ), ion diffusion coefficient (D_ff), and photovoltaic performance in the DSSC were measured. Polymer matrix absorbency and D_ff of PU-10%PPy (1.72 g g^?1, 1.52 µcm² s^?1) and PU-10%PANi (1.74 g g^?1, 1.31 µcm² s^?1) were lower than the PU matrix (2.01 g g^?1, 1.68 µcm² s^?1). However, the conductivity of PU-10%PPy and PU-10%PANi was higher than the PU matrix (2.64, 2.69, and 2.59 mS cm^?1, respectively). The efficiency of the DSSC based on PU-10%PANi was the highest, with open circuit voltage of 709 mV, short circuit current of 3.67 mA cm^?2, fill factor of 0.62, and light-to-energy conversion efficiency of 2.68%.     

A new asymmetric supercapacitor based on λ-MnO2 and activated carbon electrodes

Lithium-ion intercalated compound λ-MnO₂ was used as positive electrode in asymmetric supercapacitor with activated carbon used as negative electrode in 1 mol L^− 1 Li₂SO₄ aqueous electrolyte solution. Phase composition, morphology and particle sizes of λ-MnO₂ were studied by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrochemical capacitive performance of the asymmetric supercapacitor was tested by cyclic voltammetry and galvanostatic charge-discharge tests. The results show that the asymmetric supercapacitor has electrochemical capacitance performance within wide potential range of 0-2.2 V. The specific capacitance is 53 F g^− 1 at a constant current density of 10 mA cm^− 2. The energy density is 36 W h kg^− 1 with a power density of 314 W kg^− 1. It is obvious that λ-MnO₂ is a potential electrode material for asymmetric supercapacitor.     

A numerical scheme based on compact integrated-RBFs and Adams–Bashforth/Crank–Nicolson algorithms for diffusion and unsteady fluid flow problems

This paper presents a high-order approximation scheme based on compact integrated radial basis function (CIRBF) stencils and second-order Adams–Bashforth/Crank–Nicolson algorithms for solving time-dependent problems in one and two space dimensions. We employ CIRBF stencils, where the RBF approximations are locally constructed through integration and expressed in terms of nodal values of the function and its derivatives, to discretise the spatial derivatives in the governing equation. We adopt the Adams–Bashforth and Crank–Nicolson algorithms, which are second-order accurate, to discretise the temporal derivatives. The performance of the proposed scheme is investigated numerically through the solution of several test problems, including heat transfer governed by the diffusion equation, shock wave propagation and shock-like solution governed by the Burgers' equation, and torsionally oscillating lid-driven cavity flow governed by the Navier–Stokes equation in the primitive variables. Numerical experiments show that the proposed scheme is stable and high-order accurate in reference to the exact solution of analytic test problems and achieves a good agreement with published results for other test problems.     

A pioneering video-to-video super-resolution reconstruction algorithm based on segmentation and space–time regularisation

In view of the common existing problems in present video-to-video super-resolution reconstruction, this paper proposes a pioneering video-to-video super-resolution reconstruction algorithm based on segmentation and space–time regularisation to solve these problems. First, a video-to-video super-resolution reconstruction algorithm based on segmentation is proposed to eliminate reconstructed temporal ringing and to improve the times of reconstruction. Second, considering that image mosaic is involved in our proposed reconstruction algorithm, an improved fade-in and fade-out method is proposed to make the mosaic image looks more natural. At last, an improved space–time regularisation algorithm is put forward to remove noise and preserve image edge at the same time. Using several experiments, we prove that the proposed algorithm can achieve state-of-the -art reconstruction effect.     

A review on the interfacial intermetallic compounds between Sn–Ag–Cu based solders and substrates

The objective of this review is to study the interfacial intermatallic compounds (IMCs) between Sn–Ag–Cu based solders and common substrates, which play a crucial role in solder joints typically present in Pb-free electronics manufacturing. The microstructural evolution of IMCs at the solder/substrate interfaces is analyzed, while the models and theories describing the formation/growth mechanism of interfacial IMCs are also introduced. We focus on the influence of a variety of factors that have been reported recently, including substrates, minor alloying, mechanical stress, electromigration and thermomigration etc., as full understanding of the mechanisms that determine the formation and growth of interfacial IMCs is important to reach for developing high reliability solder joints. In the end of this review, the characteristics of the IMCs are compared and illustrated, which have marked effect on the mechanical properties and fracture behavior as well as reliability of solder joints.     

Effect of the frequency and temperature on the complex impedance spectroscopy (C–V and G–V) of p-ZnGa2Se4/n-Si nanostructure heterojunction diode

X-ray diffraction pattern and AFM results confirm the nanostructure of p-ZnGa₂Se₄/n-Si. The unit cell lattice parameters, the crystallite size L, the dislocation density δ, and the main internal strain ε were calculated. The temperature and frequency-dependent electrical characteristics of the Al/p-ZnGa₂Se₄/n-Si/Al heterojunction diode (HJD) have been investigated to determine the interface states which are responsible for the non-ideal behavior of the characteristics of the diode. The capacitance–voltage (C–V), conductance–voltage (G–V), and series resistance–voltage (R _s–V) characteristics of the diode have been analyzed in the frequency range of 5 kHz–1 MHz and temperature range of 303–423 K. The interfaces states of the diode were determined using conductance–voltage technique. The interface state density profile for the diode was obtained as a function of temperature and frequency. The values of the built-in potential V _bi, the doping concentration N _d and the barrier height φ _b(C–V) of the diode were calculated at different temperatures and frequencies. Our experimental results revealed that both the series resistance and interface state density values must be taken into account in studying the impedance spectroscopy of HJD to stand up their performance for electronic applications characteristics.     

Influence of La2O3 addition on hardness,flexural strength and microstructure of hot-pressing sintered WC–MgO bulk composites

A detailed investigation is carried out into the influences of the lanthanum oxide (La₂O₃) addition upon the microstructural characteristics and the mechanical properties of the WC–MgO composite bulk prepared by hot-pressing sintering. The results indicate that due to the unique properties of rare earth element such as high surface activity and large ionic radius, the addition of trace La₂O₃ can suppress the decarburization, promote the microstructural refinement and improve the particulate dispersion homogeneity and the particulate/matrix interfacial coherence. Consequently, the relative density of the sintered sample with 0.1 wt.% La₂O₃ addition can be increased by 4.2% as compared with the sample without La₂O₃ addition. Mechanical properties of bulks were determined by hardness test and flexural strength measurement. The results showed the possibility of preparing high hardness and fracture strength WC–MgO composite materials with the La₂O₃ added.     

Chemical stability and electrical properties of BaCe0.85Y0.15O3−δ–Ce0.85Y0.15O2−δ composite bulk samples for use as central membrane materials in dual PCFC–SOFC fuel cells

The goal of the presented research was to determine the physicochemical properties of composite samples obtained by mixing BaCe_0.85Y_0.15O_3−δ (BCY15) and Ce_0.85Y_0.15O_2−δ (YDC15) in different ratios, and to achieve a better understanding of how these ratios affect the electrical conductivity, chemical stability and morphology of BCY15–YDC15 composite materials. It was determined that the samples are chemically stable in H₂O-containing atmospheres at 600 °C. Furthermore, the porosity of the samples increases with the addition of YDC15 to BCY15. Both the porosity and the BCY15/YDC15 ratio affect the stability of the studied samples. The total activation energy (E_t) values of the composite samples, determined via resistance measurements conducted in air at temperatures between 200 and 800 °C, are in the range of 0.590 ± 0.017 eV (E_t of BCY15) to 1.132 ± 0.008 eV (E_t of YDC15). This indicates that the properties of activation energy for composite materials are additive; the presence of both BCY15 and YDC15 affects the activation energy values. The different morphologies of the samples also influence the conductivity within the respective samples. The electrical conductivity values of the composite samples obtained at temperatures from 200 to 500 °C are in the order of magnitude of 10⁻⁷–10⁻³ S/cm. These values are between those determined for pure BCY15 and YDC15 at the respective measuring temperatures. Consequently, the materials show promise for application as porous central membranes (CM) in dual PCFC–SOFC fuel cells operating in the temperature range 600–700 °C.     

3D fluid–structure-contact interaction based on a combined XFEM FSI and dual mortar contact approach

Finite deformation contact of flexible solids embedded in fluid flows occurs in a wide range of engineering scenarios. We propose a novel three-dimensional finite element approach in order to tackle this problem class. The proposed method consists of a dual mortar contact formulation, which is algorithmically integrated into an eXtended finite element method (XFEM) fluid–structure interaction approach. The combined XFEM fluid–structure-contact interaction method (FSCI) allows to compute contact of arbitrarily moving and deforming structures embedded in an arbitrary flow field. In this paper, the fluid is described by instationary incompressible Navier–Stokes equations. An exact fluid–structure interface representation permits to capture flow patterns around contacting structures very accurately as well as to simulate dry contact between structures. No restrictions arise for the structural and the contact formulation. We derive a linearized monolithic system of equations, which contains the fluid formulation, the structural formulation, the contact formulation as well as the coupling conditions at the fluid–structure interface. The linearized system may be solved either by partitioned or by monolithic fluid–structure coupling algorithms. Two numerical examples are presented to illustrate the capability of the proposed fluid–structure-contact interaction approach.