Efficient and economical dye-sensitized solar cells based on graphene/TiO2 nanocomposite as a photoanode and graphene as a Pt-free catalyst for counter electrode

Dye-sensitized solar cells have been fabricated by employing graphene/TiO₂ nanocomposites as photoanodes and graphene as a counter electrode. The mixing technique is used to prepare graphene/TiO₂ nanocomposites. The dispersion of graphene in TiO₂ is affirmed by transmission electron microscopy analysis. X-ray photoelectron spectroscopy is carried out to confirm the interstitial incorporation of carbon atoms in the TiO₂ matrix through O TiC and TiOC surface states. The electrochemical activity and stability of graphene as a catalyst for counter electrode are investigated by cyclic voltammetry and chronoamperometry measurements. Solar cells fabricated are characterized by photocurrent–voltage characteristic, Incident photon-to-current efficiency, and electrochemical impedance spectroscopy analyses. The solar cell assembled with 0.08%GR-TiO₂/N3/GR shows power conversion efficiency of 7.70%. This efficiency is superior to that of TiO₂/N3/Pt based solar cell (7.28%). The improvement in efficiency can be attributed to a fast electron transport, improved light harvesting efficiency, and enhanced electron collection at photoanodes.     

Delamination of bonding Interface between benzocyclobutene (BCB) and silicon dioxide/silicon nitride

BCB is emerging as an attractive bonding adhesive for wafer bonding in 3-D integration. Although the bonding strength of BCB is satisfactory with the assist of adhesion promoter, it is found that BCB suffers from interface delamination in harsh chemical or thermal conditions. This paper proposes, at chemical bond level, that the mechanism of interface delamination in KOH solution is attributed to the decomposition of SiOSi bonds at the interface between substrates and AP3000 adhesion promoter as a result of hydrolysis. Silicon dioxide and silicon nitride films with various densities of SiH and SiN bonds are prepared, and the bond densities are measured using infrared spectroscopy. The corresponding interface delamination rates of these films and BCB in KOH solution are measured, and the relations between the bond densities and the delamination rates are obtained for silicon dioxide and silicon nitride. It shows that the delamination rates decrease with the increase in the densities of SiOSi. These results demonstrate that the decomposition of SiOSi in KOH is the main reason for BCB delamination, and increase in the density of SiOSi improves the bonding strength.     

Liquid phase epitaxial growth of GaAs from AuGeNi melts

Epitaxial GaAs layers are grown from AuGe and AuGeNi melts in order to study Ni/AuGe/GaAs alloyed contacts. The solubility of GaAs in AuGe and AuGeNi alloys has been measured. The electrical behavior of Au, Ge and Ni in Ni/AuGe/GaAs alloyed contacts is also discussed. Based on the results of liquid phase epitaxial growth experiments, we suggest the conditions for making ohmic contacts with low specific contact resistance on n-type GaAs by AuGeNi alloys. The specific contact resistance of Ni/AuGe/GaAs alloyed contacts is also measured.     

Enhanced photovoltaic performance in inverted polymer solar cells using Li ion doped ZnO cathode buffer layer

We have proposed an approach to improve the photovoltaic performance of inverted polymer solar cells (i-PSC) using lithium ion doped ZnO (LiZnO) as cathode buffer layer (CBL). The LiZnO CBL was prepared using the diffusion technique, performed by inducing the Li ion of 8-hydroxyquinolatolithium (Liq) to diffuse into ZnO film through annealing the bi-layer ZnO/Liq film. Doping concentration of Li ion was controlled by using various thickness of Liq film and annealing temperature. Based on LiZnO CBL, the poly (3-hexylthiophene) [6,6]:-phenyl C61-butyric acid methyl ester (P3HT:PCBM) i-PSC device possessed a optimal power conversion efficiency (PCE) of 4.07%, which was 30% improved than that of the device with neat ZnO as CBL. The enhancement of the device performance could be attributed to the enhanced electron mobility and better band matching of the LiZnO CBL. Our finding indicates that the LiZnO film fabricated with relatively low temperature treatment has great potential for high-performance i-PSCs.     

Strength and reliability of low temperature transient liquid phase bonded CuSnCu interconnects

As power electronic devices have tendencies to operate at higher temperatures and current densities, the demand for reliable and efficient packaging technologies are ever increasing. This paper reports the studies on application of transient liquid phase (TLP) bonding of CuSnCu systems as a potential technology that could enable the realization of stacks with better thermal performance and reliability than those can be achieved using conventional soldering techniques. Low temperature TLP bonded CuSnCu samples are fabricated, and the strength of the achieved bonds is measured by shear testing. Micro-sectioning and optical microscopy studies of the samples reveal that the TLP bonds show good homogeneity with a small number of voids at the interface. Energy dispersive X-ray analysis is applied to examine at what rates Sn is converted into CuSn intermetallics since a full conversion is critical for achieving a strong and high temperature resistant bond. Finally, initial results from a thermal cycling test are presented and it is concluded that the achieved TLP bonding is a promising candidate for the fabrication of reliable interconnects in power electronics.     

Using nanoindentation to investigate the temperature cycling of Sn37Pb solders

Using nanoindentation and energy dispersive X-ray spectrometry (EDS), we have conducted an investigation into corner failures to elucidate not only the nanomechanical properties of Sn37Pb solder balls but also the effects of temperature cycling tests (TCTs). We found that the hardness of Sn37Pb solder balls was greater in central locations [1.18 ± 0.05 GPa for room-temperature (RT) sample; 1.3 ± 0.05 GPa for TCT sample], but had standard values in corner locations (> 0.2 ± 0.02 GPa). The modulus increased after the TCTs. Nevertheless, the mechanical properties were closely related to the average area of the α-Pb phase. The average area of the Pb-rich region was more stable after the TCTs than that of the RT sample, due to the enhanced mechanical properties of the Sn37Pb solder, suggesting good reliability. From an analysis of average areas in the RT sample, it appears that the Pb-rich solid solution that formed led to weak SnPb bonds near the corner locations. Electron back-scattered diffraction measurements revealed that grains with grain boundaries formed as a result of accelerated TCT cycling. We conclude that SnPb recrystallization was initiated and propagated after the TCTs, followed by propagation to the interfacial region.     

Microstructures and properties of Bi10Ag high temperature solder doped with Cu element

High temperature Bi10Ag solders with different amounts of Cu were used to investigate the impacts of Cu on the microstructures, melting characteristics, wettability and shear strength of the Bi-10Ag-xCu (x = 0, 0.5, 1, and 2 wt%) solders. A metastable Cu-rich phase was formed due to the addition of Cu. The Cu has negligible effect on the solidus but it can decrease about 6 °C on the liquidus. Doped with 0.5 wt% of Cu, the solders showed the largest melting range in the DSC curves and improved wettability on Cu substrates. When the Cu addition excesses to 0.5 wt%, it will induce negative effects on wettability of the solders on the substrate. Moreover, the addition of Cu has no significant influence on the strength of the Bi10Ag lap solder joints. The Bi-10Ag-0.5Cu solder joint has higher shear strength than that of Pb5Sn.     

Computational protocol to predict hyperpolarizabilities of large π-conjugated organic push–pull molecules

The first hyperpolarizability (β) for a set of 21 large π-conjugated organic push–pull molecules is predicted using an affordable computational protocol. Static -β(0)- and frequency-dependent -β(−2ω; ω,ω)- total first hyperpolarizability were calculated, using density functional theory (DFT) at the cam-B3LYP/NLO-V// level, where the NLO-V basis set was developed specifically for predicting nonlinear optics (NLO) properties. The average absolute deviations were 158 and 392 (in units of 10⁻³⁰ esu) for β(0) and β(0.67 eV), respectively, in the gas phase. These errors correspond, on average, to 49% and 65% of the experimental values. The inclusion of solvent effects (CHCl₃) through a continuum model slightly improves the predictions of β(0.67 eV), with absolute error decreasing to 265 (in units of 10⁻³⁰ esu), corresponding to an error of 35%. For the julolidinyl-(CHCH)₂–C(CH₃) = CH–CHCH–CHC(CH₃)–CHCH–CHN,N'-diethylthiobarbituric acid (molecule st_5_6, Graphical Abstract), which presents the highest NLO response among the compounds analyzed, the calculated value for μβ(0.67 eV) in CHCl₃ was 40,255 × 10⁻⁴⁸ esu, in satisfactory accordance with the experimental data, 34,779 × 10⁻⁴⁸ esu (an error of 16% only). In addition, the two-states approach was applied for the set of molecules studied, and the results showed that the increase in total β is explained well by the charge transfer excitation, involving the frontier orbitals. Therefore, the computational protocol, based on the cam-B3LYP/NLO-V// level, should be considered an affordable and reliable calculation scheme to predict very high first hyperpolarizability for large π-conjugated organic molecules.     

Unveiling photophysical properties of phenanthro[9,10-d]imidazole derivatives for organic light-emitting diodes

Recently, two phenanthro[9,10-d]imidazole derivatives exhibited excellent advantages in organic light-emitting devices (i.e. high luminous efficiency, high carrier mobility, and low turn-on voltage). However, the relationship between their photophysical properties and the structural characters or intermolecular interactions remain elusive, which is considerable importance to further performance improvement. Currently, density functional theory (DFT) and time-dependent DFT (TD-DFT) have become powerful tools to rationalize photophysical properties and to design new materials with improvement performance. The simulated electron absorption and emission wavelengths of compounds 1 and 2 are in good agreement with the experimental ones. For the studied compounds, the involvement of tert-butyl moiety has negligible effect on energy level and distribution of frontier molecular orbitals (FMOs), whereas greatly affects electron transition of deep energy level and charge transport property. Synergy of π-π and CH···π intermolecular interactions is responsible for the bipolar carrier transport, while CH···π for hole transport. The incorporation of NH₂ on phenanthro[9,10-d]imidazole and NO₂ on diphenylamino part is an effective way to tune FMOs energy level and intramolecular charge transfer, leading to the substantial enhancement of the second-order nonlinear optical (NLO) response. Our work is also important for understanding photophysical properties and designing photoelectric materials of phenanthro[9,10-d]imidazole derivatives.     

XPS analysis of the chemical degradation of PTB7 polymers for organic photovoltaics

The chemical degradation of the Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] or ‘ PTB7’ has been studied using X-ray Photoelectron Spectroscopy (XPS). This material system appears to be intrinsically unstable especially when illuminated in air and XPS studies confirm the rapid photo-degradation is related to changes in chemical structure of the polymer. In particular, XPS spectra show an initial reduction in relative CC intensity, suggests loss of the alkoxy side chains. This is followed by a dramatic increase in the level of oxygen-bonded species, especially CO at ∼286.5 eV and C(=O)O at 289.2 eV, indicative of COOH and OH group formation, and oxidation of S. The XPS results support the view that using processing additives reduces the chemical stability of the polymer and provides insight into strategies to improve molecular design to ensure higher chemical stability.     

Solderless bonding with nanoporous copper as interlayer for high-temperature applications

The Cu₄₀Al₆₀ alloy has been developed as the precursor alloy to fabricate nanoporous copper (NPC) sheets through chemical dealloying in 1.6 mol/L dilute hydrochloric acid solution at various temperatures. A nanoporous structure with uniform pore distribution and size formed after the bath temperature exceeded 80 °C. The CuCu interconnection was achieved by inserting the NPC sheet as an interlayer and reflowing without solder under a pressure of 10 MPa. After bonding, the thickness of NPC layer was greatly reduced and the porous structure was densified. The average shear strength of the bondlines was measured to be 22.10 MPa, and the bondlines exhibit a low electrical resistivity of 9.65 μΩ·cm. The Vickers hardness and shear strength of the bondline increased after aging at 150 °C for different time due to the densified porous structure. This work demonstrated that the NPC sheets can be used to achieve the CuCu interconnection, which is a potential bonding technology for power devices operating at high temperature.     

Tuning the IV characteristic of a cruciform diamine molecular device by connected position and B/N doping

By performing first-principle quantum transport calculations, we investigate the effects of connected position and B/N doping on the transport properties of a single cruciform diamine molecule connected to zigzag graphene nanoribbon leads. The negative differential resistance behaviors are found in IV characteristics of the undoped molecular device. The peak-to-valley current ratio can be modulated obviously by changing the connected position. Then, we find the B/N doped effects are sensitive to doping site in the connected region. The replacement of B/N atom on R1 (carbon atom in connected region close to the zigzag graphene nanoribbon) seldom affects the transmission spectrum around Fermi level. But, the replacement of B/N atom on R2 (carbon atom in connected region close to the molecule) can raise the transmission coefficient around Fermi level markedly leading to the large growth of the current at the low biases. In addition, the replacement of N atom on R2 can induce a negative differential resistance behavior in IV curve at low bias region.     

Influence of ionic Bismuth on intrinsic defects in ZnO varistors

The relationship between the dielectric dissipation factor D(tan δ) and frequency in the varistors of ZnO–Sb₂O₃–BaO and ZnO–Bi₂O₃–Sb₂O₃–BaO system ceramics has been investigated. A new dielectric dissipation peak was found near 1.5 MHz at room temperature in the ZnO–Sb₂O₃–BaO system, and the corresponding electron trapping level is about 0.18 eV. The dissipation peak was considered to result from the intrinsic defect ${\text{Zn}}_{\text{i}}^{\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph><mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}}$. The additive Bi₂O₃ may play a suppressing effect on the formation of ${\text{Zn}}_{\text{i}}^{\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph><mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}}$. This assumption was consistent with the experimental fact that degradation phenomenon of varistor ceramics under long-term load voltage is improved by the increasing amount of Bi₂O₃ additive.     

Aqueous solution-processed InCl3 as an effective buffer layer to improve hole injection in simplified phosphorescent organic light emitting diodes

An effective anode buffer layer is demonstrated by aqueous solution-processed indium trichloride (sInCl₃) in simplified phosphorescent organic light emitting diodes (PhOLEDs). The hole injection is improved in sInCl₃ based PhOLEDs exhibiting better performance with decreased driving voltage, increased power efficiency compared to the traditional ultraviolet-ozone (UV-Ozone) treated ones. Then, the mechanism for the enhanced hole injection is investigated. Better electrode contact is found in sInCl₃ based hole dominated devices. Higher work function (∼0.60 eV) is detected on the sInCl₃-ITO anode and stable InCl bonds are formed on its surface compared to the UV-Ozone treated one according to the photoelectron spectroscopy.     

Effect of ENEPIG metallization for solid-state gold-gold diffusion bonds

Gold-gold (AuAu) diffusion bonding behavior of different tri-layer thicknesses of Electroless Ni/Electroless Pd/Immersion Au (ENEPIG) plating on a high-density system on a flex (SOF) package was examined. Plating thickness has a significant effect on surface roughness and void formation at the AuAu bonding interface, which exhibits degraded bond strength with an affected failure mode. It is seen that relatively smooth surface roughness (Ra < 100 nm) of thicker Ni(P) plating samples facilitates the shrinkage of voids and significantly increases bonding strength. Higher surface roughness in the low Ni(P) sample has a poor surface profile, which results in large lenticular shape voids and requires more energy to shrink by diffusion and a creep process. Enhancing bonding parameters constitutes an essential feature to compensate the physical and mechanical properties of ENEPIG plating. Based on this study, the authors recommend a suitable ENEPIG plating thickness for a high quality metallurgical bond, which passes different reliability tests.     

Theoretical insights into the ultrafast excited-state intramolecular proton transfer (ESIPT) mechanism in a series of amide-based NH⋯N hydrogen-bonding compounds

Excited-state intramolecular proton transfer (ESIPT) has many important potential applications. In this paper, the geometries of a series of amide-based NH⋯N hydrogen-bonding compounds in their ground S₀ states and first excited singlet S₁ states were optimized with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches. Both topological analysis and noncovalent interactions analysis show strong intramolecular hydrogen-bonds in the studied five systems and the electron density function ρ(r) exhibits good linear relationship with the distance of H⋯N₂. The potential energy curves of the S₀ and S₁ states were scanned by using of DFT and TD-DFT to elucidate the ESIPT process. It reveals that all the systems considered here can undergo an ultrafast ESIPT reaction, with energy barrier of less than 0.05 eV, giving rise to the single fluorescence emission from the proton-transfer tautomer. It is also found that the shorter the hydrogen bond in the normal-form S₁ state, the easier the ESIPT takes place.     

Preparation and thermoelectric properties of PEDOT:PSS coated Te nanorod/PEDOT:PSS composite films

PEDOT:PSS coated Te (PCTe) nanorod/PEDOT:PSS composite films were prepared by a drop-casting technique. H₂SO₄ treatment was employed to enhance thermoelectric (TE) properties of the composite films. The addition of PCTe nanorods increased both the electrical conductivity and the Seebeck coefficient of the composite films. An optimized power factor of 141.9 μW/mK² was obtained for the film containing 90 wt% PCTe nanorods treated with 12 M H₂SO₄ at room temperature, which was 2.75 times as high as that of the untreated composite film, corresponding to the electrical conductivity and Seebeck coefficient of 204.6 S/cm and 83.27 μV/K, respectively. XPS and GIWAXS analysis revealed the removal of insulating PSS units and the rearrangement of PEDOT chains after the H₂SO₄ treatment. Finally, a 9-leg TE generator prototype was fabricated using the optimized composite film. The maximum output power and area output power density produced from the prototype were 47.7 nW and 57.2 μW/cm², respectively, at the temperature difference of 40 K.     

Low temperature CuCu thermo-compression bonding with temporary passivation of self-assembled monolayer and its bond strength enhancement

Self-assembled monolayer (SAM) of alkane-thiol is formed on copper (Cu) thin layer coated on silicon (Si) wafer with the aim to protect the surface against excessive oxidation during storage in the room ambient. After 3 days of storage, the temporary SAM layer is desorbed with in situ anneal in inert ambient to uncover the clean Cu surface. A pair of wafers is bonded at 250 °C. Clear evidences of in-plane and out-of-plane Cu grain growth are observed resulting in a wiggling bonding interface. This gives rise to enhancement in shear strength in the bonded CuCu layer.     

Adsorption/photocatalytic performances of hierarchical flowerlike BiOBrxCl1−x nanostructures for methyl orange,Rhodamine B and methylene blue

We synthesized hierarchical flower-like BiOBr_xCl_1−x (0≤x≤1) microspheres in ethylene glycol solvent and examined their fundamental properties by scanning electron microscopy (SEM), X-day diffraction (XRD), UV–visible absorption, Raman, photoluminescence spectroscopy, and BET surface area measurement. Additionally, their adsorption and photocatalytic performance were tested using methyl orange (MO), Rhodamine B (RhB), and methylene blue (MB). The adsorption performance was found to be in the order of BiOCl<BiOBr_xCl_1−x<BiOBr for MO under dark conditions. For the selected BiOBr_0.7Cl_0.3 catalyst, the adsorption ability was found to be in the order of MO⪯¡RhB<MB owing to electrostatic interactions between the catalyst and the dye. The photocatalytic dye degradation performance occurred in the order of MB<MO⪯¡RhB as a result of light absorption by the dye followed by good electron transfer from the conduction band of the dye to that of the catalyst. An indirect chemical probe method was used to examine the roles of active species in the dye-sensitized photodegradation mechanism, which were found to be in the order of OH≈O₂⁻<h⁺ under visible light irradiation.     

Enhanced photocatalytic activity of sulfated silica-titania composites prepared by impregnation using ammonium persulfate solution

Sulfate (SO₄²⁻) modified silica–titania (SiO₂–TiO₂) composite photocatalysts with different loadings of SO₄²⁻ were prepared by a facile pore impregnating method using ammonium persulfate (NH₄)₂S₂O₈ solution. The surface parameters, structure, morphology, the adsorption ability of light, the binding energy of Ti2p and O1s, and the formation rate of OH radicals produced during the photocatalytic reaction process were characterized by the Brunauer–Emmett–Teller (BET) method, X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and terephthalic acid photoluminescence probing technique (TA-PL), respectively. The results reveal that sulfating of SiO₂–TiO₂ induces the shift of Ti2p and O1s, and increases the adsorption of rhodamine B on the sulfated photocatalysts and the formation rate of OH radicals produced during the photocatalytic reaction process. The photocatalytic activity of SO₄²⁻/SiO₂–TiO₂ for de-colorization of rhodamine B aqueous solution was evaluated. The result shows that when wt% of SO₄²⁻ is 8.6%, SO₄²⁻/SiO₂−TiO₂ exhibits the best photocatalytic activity under ultraviolet light irradiation and the possible reason is discussed.