Effect of ex-situ hydrogen passivation on the structural properties of e-beam evaporated amorphous silicon thin film for solar cell applications

Thin-film photovoltaics greatly reduce the semiconductor material content in the finished product, using 150–200 times less material as compared with conventional Si wafer based cells. Electron beam evaporation (e-beam), a non-ultra-high vacuum technique has the potential for being inexpensive, and simpler process for a-Si deposition. It offers specific advantages such as high Si deposition rate (up to 1 μm/min), excellent Si source material usage, avoidance of toxic gases, and simple sample preparation conditions. In this work, we report the growth of a-Si films using e-beam at a growth rate exceeding 30 Å/s (1–5 Å/s for conventional PECVD process). We report the effect of hydrogen passivation on amorphous silicon network and on silicon-bonded hydrogen configuration under ex-situ hydrogenation in hydrogen plasma. The hydrogen concentration and silicon-hydrogen bonding configuration was evaluated using nuclear reaction analysis (NRA) and Fourier transform infrared spectroscopy (FTIR). Hydrogen plasma treatment shows an increase in the monohydride bond concentration with substrate temperature, and is corroborated by our FTIR investigation, in addition to reducing clustered monohydride bonds or polyhydride bonds in a-Si:H film. Raman analysis indicates reduction in silicon bond angle as well as the bond distance, both leading to significant structural improvement in short-range and medium range order in the amorphous phase. Thus, ex-situ hydrogenation clearly demonstrates the possibility of comparable hydrogen passivation in e‐beam evaporated a-Si films with high growth rate. One can easily extrapolate this result to microcrystalline film growth, assuming the structural improvement of the silicon network preceding the microcrystalline nucleation, where ex-situ passivation is most effective. Thus ex-situ hydrogenation opens up new possibilities in minutely tailoring the a:Si film properties especially for solar cell applications.     

Dopant induced morphology changes in ZnO nanocrystals

Zinc oxide (ZnO) nanocrystals doped with different groups of impurities, e.g., Li, Na, Cu, Pr and Mg synthesized by solid-state reaction method under similar conditions exhibit different morphology. XRD showed monophasic wurtzite structure but change in lattice parameters and Zn-O bond length indicates incorporation of dopant ion in ZnO lattice. The morphology of ZnO nanocrystals exhibited striking dependence on type of dopant ion with the shape changing from nanorods, spherical to petal like particles. Photoluminescence (PL) shows pronounced UV emission and negligible visible emission for Li, Na and Cu doped ZnO nanocrystals with peak positions coinciding with that of undoped ZnO. Whereas signature emission of Pr³⁺ ion as well as broad visible emission from Mg doped ZnO revealed the role of intra gap metastable states formed by the dopant ion in the emission process.     

Intrinsically Low Thermal Conductivity and High Carrier Mobility in Dual Topological Quantum Material,n‐Type BiTe

A challenge in thermoelectrics is to achieve intrinsically low thermal conductivity in crystalline solids while maintaining a high carrier mobility (μ). Topological quantum materials, such as the topological insulator (TI) or topological crystalline insulator (TCI) can exhibit high μ. Weak topological insulators (WTI) are of interest because of their layered hetero‐structural nature which has a low lattice thermal conductivity (κ_lat). BiTe, a unique member of the (Bi₂)_m(Bi₂Te₃)_n homologous series (m:n=1:2), has both the quantum states, TCI and WTI, which is distinct from the conventional strong TI, Bi₂Te₃ (where m:n=0:1). Herein, we report intrinsically low κ_lat of 0.47–0.8 W m^?1 K^?1 in the 300–650 K range in BiTe resulting from low energy optical phonon branches which originate primarily from the localized vibrations of Bi bilayer. It has high μ≈516 cm² V^?1 s^?1 and 707 cm² V^?1 s^?1 along parallel and perpendicular to the spark plasma sintering (SPS) directions, respectively, at room temperature.     

Cobalt‐Catalyzed Intermolecular C(sp2)O Cross‐Coupling

Cobalt(II)‐catalyzed C(sp²)?O cross‐coupling between aryl/heteroaryl alcohols and vinyl/aryl halides in the presence of Cu^I has been achieved under ligand‐free conditions. In this reaction, copper plays a significant role in transmetalation rather than being directly involved in the C?O coupling. This unique Co/Cu‐dual catalyst system provides an easy access to a library of aryl–vinyl, heteroaryl–styryl, aryl–aryl, and heteroaryl–heteroaryl ethers in the absence of any ligand or additive.     

Diisopropylethylammonium acetate (DIPEAc): An efficient and recyclable catalyst for the rapid synthesis of 5-substituted-1H-tetrazoles

A simple and efficient protocol developed for the synthesis of 5-substituted 1H-tetrazole derivatives through [2+3] cycloaddition reaction between benzonitriles and sodium azide using diisopropylethylammonium acetate as a recyclable reaction medium is described. The reactions proceed well at 80?°C and provide the corresponding tetrazoles in good to excellent yields (up to 94% yield). Developed method has notable advantages, such as simple and mild conditions, easy workup, reusability with consistent catalytic activity, and safer alternative to hazardous, corrosive conventional Lewis acid catalysts.     

EPR and optical study of Mn2+ doped ammonium tartrate single crystals

EPR study of Mn2+ doped ammonium tartrate single crystals is carried out at room temperature. The spin Hamiltonian parameters are: gx=1.9225+/-0.0002, gy=1.9554+/-0.0002, gz=2.1258+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(191+/-2) x 10(-4) cm(-1), E=(61+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site I and gx=1.9235+/-0.0002, gy=1.9574+/-0.0002, gz=2.0664+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(180+/-2) x 10(-4) cm(-1), E=(57+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site II, respectively. The observed optical bands are fitted with inter-electronic repulsion parameters (B and C), crystal field parameter (Dq) and Trees correction (alpha) and the values found are B=752, C=2438, Dq=765 and alpha=76 cm(-1). The data obtained are further used to discuss the surrounding crystal field and the nature of metal-ligand bonding in the crystal.     

One‐Pot Three‐Component Synthesis of 2‐Amino Pyrimidines in Aqueous PEG‐400 at Ambient Temperature

Amino pyrimidines have been synthesized by a one‐pot procedure under environmentally friendly reaction conditions at room temperature. The use of aqueous PEG‐400 circumvents the problems associated with the toxic, hazardous organic solvents and oxidizing agents.     

Bulk heterojunction solar cells made from carbazole copolymer and fullerene derivative with an inserted layer of discotic material with improved efficiency

Bulk heterojunction photovoltaic cells based on composites of copolymer poly [N-90-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] and the fullerene derivative [6,6]-phenyl C71-butyric acid methyl ester with an inserted layer of discotic liquid crystalline material (2, 3, 6, 7, 10, 11-hexabutyloxytriphenylene) between the interface of active layer and hole transporting layer has been reported. Different hole transporting layers deposited on indium tin oxide substrates such as poly (3,4-ethylenedioxythiophene)-poly (styrenesulphonate) or molybdenum trioxide has been used in these devices. All the devices with inserted discotic liquid crystal layer showed better performance than the reference cells. Power conversion efficiency of 5.14% was achieved for these photovoltaic solar cells containing self-organised discotic liquid crystal layer of 30 nm thickness under one sun condition which is substantial jump as compared to earlier reports. The mobility of holes in the discotic liquid crystal inserted devices was found to be of the order of 10^–6 cm² V^–1 s^–1 due to which high values of current density was achieved. The influence of varying the thickness of liquid crystal layer and annealing on the photovoltaic parameters of these devices was also studied.     

Impact of metal ions (Cr3+, Co2+, Ni2+, Cu2+ and Zn2+) substitution on the structural,magnetic and catalytic properties of substituted Co–Mn ferrites synthesized by sol–gel route

Journal of Sol-Gel Science and Technology - Manganese substituted cobalt ferrites (CoMn x Fe2?x O4, x?=?0.2, 0.4, 0.6, 0.8 and 1.0) synthesized using sol gel autocombustion method...     

Design,synthesis and biological evaluation of antimalarial activity of new derivatives of 2,4,6-<Emphasis Type="Italic">s</Emphasis>-triazine

Dihydrofolate reductase (DHFR) is an important enzyme for de novo synthesis of nucleotides in Plasmodium falciparum and it is essential for cell proliferation. DHFR is a well known antimalarial target for drugs like cycloguanil and pyrimethamine which target its inhibition for their pharmacological actions. However, the clinical efficacies of these antimalarial drugs have been compromising due to multiple mutations occurring in DHFR that lead to drug resistance. In this background, we have designed 22 s -triazine compounds using the best five parameters based 3D-QSAR model built by using genetic function approximation. In-silico designed compounds were further filtered to 6 compounds based upon their ADME properties, docking studies and predicted minimum inhibitory concentrations (MIC). Out of 6 compounds, 3 compounds were synthesized in good yield over 95% and characterized using IR, ¹HNMR, ¹³CNMR and mass spectroscopic techniques. Parasitemia inhibition assay was used to evaluate the antimalarial activity of s -triazine compounds against 3D7 strain of P. falciparum. All the three compounds (7, 13 and 18) showed 30 times higher potency than cycloguanil (standard drug). It was observed that compound 18 was the most active while the compound 13 was the least active. On the closer inspection of physicochemical properties and SAR, it was observed that the presence of electron donating groups, number of hydrogen bond formation, lipophilicity of ligands and coulson charge of nitrogen atom present in the triazine ring enhances the DHFR inhibition significantly. This study will contribute to further endeavours of more potent DHFR inhibitors.