Bhabani S. Swain

Highly efficient perovskite solar cells based on a nanostructured WO3–TiO2 core–shell electron transporting material

Until recently, only mesoporous TiO2 and ZnO were successfully demonstrated as electron transport layers (ETL) alongside the reports of ZrO2 and Al2O3 as scaffold materials in organometal halide perovskite solar cells, largely owing to ease of processing and to high power conversion efficiency. In this article, we explore tungsten trioxide (WO3)-based nanostructured and porous ETL materials directly grown hydrothermally with different morphologies such as nanoparticles, nanorods and nanosheet arrays. The nanostructure morphology strongly influences the photocurrent and efficiency in organometal halide perovskite solar cells. We find that the perovskite solar cells based on WO3 nanosheet arrays yield significantly enhanced photovoltaic performance as compared to nanoparticles and nanorod arrays due to good perovskite absorber infiltration in the porous scaffold and more rapid carrier transport. We further demonstrate that treating the WO3 nanostructures with an aqueous solution of TiCl4 reduces charge recombination at the perovskite/WO3 interface, resulting in the highest power conversion efficiency of 11.24% for devices based on WO3 nanosheet arrays. The successful demonstration of alternative ETL materials and nanostructures based on WO3 will open up new opportunities in the development of highly efficient perovskite solar cells.

Highly Efficient Hybrid Photovoltaics Based on Hyperbranched Three‐Dimensional TiO2 Electron Transporting Materials

Part of this work was supported by Round 2 of the Collaborative Research Grant from the Office of Competitive Research Funds and by the Career Development SABIC Chair held by AA.

Micro-Raman and FTIR Analysis of Silicon Carbo-Nitride Thin Films at Different H 2 Flow Rate

Silicon carbo-nitride thin films were deposited on Si (100) substrate by thermal chemical vapour deposition using C2H2 and Si powder precursors. The thin films were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy and Raman spectroscopy. The FTIR spectra reveals the presence of vibration signature of various bonds at 512, 1135, 1688, 2444, 3032, 3550 cm−1 which correspond to Si–N, SiC–N, C–N, Si–H, C–H and N–H, respectively, in the SiCN thin films. Raman spectra reveal the presence of three prominent stoke shifts at 617, 1141 and 1648 cm−1 corresponding to Si–H, SiC–N and C–C respectively. The vibrational signature of SiC–N shifted from 1126 to 1050 cm−1 with increase in H2 flow rate indicates formation of nanosized cluster in deposited thin film .

Analysis of Chemical Bonding and Structural Network of Gold Silicide in Core–Shell Silicon Nanowire

The Au-catalyzed core–shell silicon nanowires (Si-NWs) were synthesized by chemical vapor deposition by using SiH4 and H2 precursor gases. The TEM and FTIR studies revealed that the Si-NWs consist of core silicon surrounded by a thick oxide sheath and Au distributed at the a-SiOx/Si interface. The x-ray photoelectron spectroscopy (XPS) was used to study the chemical composition and electronic environments of gold silicide in the a-SiOx/Si-NWs. The elemental analysis and chemical network of gold silicide of core–shell Si-NWs were explained on the basis of the random atomic distribution of Si, O and Au atoms. The Raman spectra and XRD peak reveal the crystalline core of Si-NWs. The individual contribution to the Au (4d) core orbital was deconvoluted to Au-Si-Au, Au-Si-O, Au-Au, Au-O-Au, Au-O-Si and Au=O/Au-O2 bonding structure. The analysis shows that the O linked with Si and Au has also contributed to growth of Si-NWs.

Biocompatibility of Hydrogen-Diluted Amorphous Silicon Carbide Thin Films for Artificial Heart Valve Coating

Amorphous silicon carbide (a-SiC:H) thin films were synthesized using trichloromethylsilane by a hot wire chemical vapor deposition process. The deposited films were characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, x-ray diffraction and x-ray photoelectron spectroscopy to confirm its chemical bonding, structural network and composition of the a-SiC:H films. The optical microscopy images reveal that hydrogen dilution increased the surface roughness and pore density of a-SiC:H thin film. The Raman spectroscopy and FTIR spectra reveal chemical network consisting of Si-Si, C-C and Si-C bonds, respectively. The XRD spectroscopy and Raman spectroscopy indicate a-SiC:H still has short-range order. In addition, in vitro cytotoxicity test ensures the behavior of cell–semiconductor hybrid to monitor the proper coordination. The live–dead assays and MTT assay reveal an increase in green nucleus cell, and cell viability is greater than 88%, respectively, showing non-toxic nature of prepared a-SiC:H film. Moreover, the result indicated by direct contact assay, and cell prefers to adhere and proliferate on a-SiC:H thin films having a positive effect as artificial heart valve coating material.

Synthesis and characterization of TiO2 nanostructure thin films grown by thermal CVD

Thermal Chemical Vapor Deposition (CVD) deposited Titanium dioxide nanostructures (TiO2-NSs) were grown by using Ti powder and O2 precursors on Si/SiO2 (100) substrate. The microstructure and vibration properties of TiO2-NSs were characterized by Fourier transform infrared (FTIR), SEM, and photoluminescence (PL) spectroscopy. The role of O2 flow rate on TiO2-NSs revealed decreased deposition rate, however, surface roughness has been increased resulted into formation of nanostructure thin films.

Investigation of phonon modes in gallium nitride nanowires deposited by thermal CVD

Gallium nitride nanowires (GaN-NWs) of diameters ranging from 20 to 80 nm were grown on the p-type Si substrate by Thermal Chemical Vapor Deposition (TCVD) using Iron (Fe) catalyst via VLS mechanism. Raman and FTIR spectra reveal the presence of broad transverse optic (TO) and longitudinal optic (LO) phonon peak spreads over 500-600 cm−1 and 720 cm−1 respectively. The detail deconvolution of integrated transverse and longitudinal phonon analysis reveals phonon confinement brought out by incorporation of hydrogen atom. The red shifts of TO and LO phonon peak position indicates nanosized effect. IA1(LO)/IA1(TO) increases from 0.073 to 1.0 and their respective fwhmA1(LO)/fwhmA1(TO) also increases from 0.71 to 1.31 with increasing H2 flow rate. E1(LO) - E1(TO) and A1(LO) - A1(TO) increases from 173.83 to 190.73 and 184.89 to 193.22 respectively. Apart from this usual TO and LO phonon, we have found Surface Optic (SO) phonon at 671 cm−1 in FTIR spectra. The intensity of PL peak increases with increasing H2 dil...

Optoelectronic properties of Indium-assisted Gallium Nitride Nanowires

In this work, the optoelectronic properties of H2 diluted Gallium Nitride Nanowires (GaN-NWs) grown on Si substrate were examined. The GaN-NWs were deposited on Indium (In) coated p-type Si substrate by thermal chemical vapor deposition process using GaN powder and pure N2, H2 as precursor gases. A variety of techniques such as Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) Spectroscopy, Raman Spectroscopy and Photoluminescence (PL) Spectroscopy were used to characterize the grown materials. PL spectra reveals a broad emission band ranging from 2.5 eV to 3.2 eV with intense peak centered at 2.92 eV which is red shifted with respect to bulk GaN (3.4 eV). This might be due to the formation of different electronic energy bands in the presence of H2 and In catalyst which breaks the periodicity of the lattice and modifies the band structure locally.