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In present study, hollow urchin-like nanostructures of Nb2O5 with elongated nanofilaments as photoanode material for dye-sensitized solar cells (DSSCs) are successfully synthesized at different reaction times (viz. 12, 24, and 40 h, respectively, named as samples NB-1, NB-2, and NB-3) using facile hydrothermal route. We have studied the significant influence of hydrothermal reaction time on the structural, optical, morphological, and electrical properties. The photovoltaic performance of different samples is understood from response of current-potential (J-V) curve and incident photon-to-current efficiency (IPCE) while charge recombination behavior and resistance of the cells are studied by electrochemical impedance spectroscopy (EIS). The X-ray diffraction (XRD) study shows the orthorhombic crystalline form for the synthesized samples. Electron microscopy studies confirm the formation of porous spherical morphology with hairy filaments protruding outward. Size of urchin-like particle is found to be in the range of about 1 μm diameter, and the filaments emerging out from the surface of hollow spheres are seen to be 30–70 nm long and 5–20 nm in diameter. The DSSCs fabricated from the resultant nanostructures show the better photovoltaic performance with Nb2O5 sample synthesized at 24-h reaction time. The Jsc and efficiency for NB-2 are 8.24 mAcm−2 and 3.58% respectively, which are better than corresponding samples synthesized at the reaction time of 12 h and 40 h, respectively. These photovoltaic results obtained from the DSSCs fabricated using Nb2O5 nanostructures are comparatively exciting with TiO2 spheres. By further optimizing reaction conditions, it is expected that niobium pentoxide can emerge as better semiconductor oxide for photovoltaic and optical devices.

In dye-sensitized solar cells (DSSCs), the semiconductor photo-anode film plays a significant role in enhancing the overall power conversion efficiency. ZnO is considered as the futuristic hope for photoanodes in DSSCs due to manifold properties over TiO2. However, the power conversion efficiency of ZnO-based DSSCs is still low due to its poor chemical stability and surface defects. In this work, we reported the synthesis of ZnO nano-flowers as well as its surface modification of with TiCl4 at different concentration. In DSSCs, the enhancement in power conversion efficiency results suggested that surface modification of ZnO film by TiCl4 leads to the deposition of TiO2 which subsequently increases the roughness factor of film as well as scattering layer. This preferential surface modification of ZnO film facilitates the accumulation of large number of photo-injected electrons in the HOMO of the photoanode with rapid transfer of charge carriers to FTO via ZnO layer by lowering the recombination of photo-injected electrons with the redox electrolyte as well as oxidized dye. The intensity-modulated photocurrent spectroscopy (IMVS) and intensity-modulated photovoltage spectroscopy (IMPS) study also indicated that the recombination rate decreased considerably during the electron transportation. The ZnO film surface modified by TiCl4 achieved a power conversion efficiency of 4.48%, which is two times higher than that of the non-modified ZnO photoanode.

Hierarchically nano-structured ZnO microspheres have been synthesized solvothermally at variable reaction times (6, 12, 36, and 48 h) by using ethylene glycol as a solvent, zinc acetate as precursor, and hexamethylene triamine (HMT) as structure directing agent. The study also focused on the mechanism of time-dependant growth of hierarchical ZnO microspheres and their deployment in dye-sensitized solar cells (DSSCs) as photoanode. Longer reaction times lead to formation of nearly spherical ZnO microspheres. The structural and morphological analysis reveals the formation of a wurtzite hexagonal crystalline structure having a microsphere-like morphology. ZnO hierarchical microspheres synthesized at different reaction times have been used as photoanode in DSSCs which show enhanced light-harvesting properties than the commercial ZnO powders. ZnO microspheres synthesized at 48 h show maximum current density and cell efficiency of 8.51 mA/cm2 and 3.31%, respectively. This enhancement in photovoltaic parameters could be due to highly porous microspheres which provide more specific surface area for dye loading, retardation of recombination, and better charge transport.

The SnO/SnO2 nanocomposites were synthesized using semisolvothermal reaction technique. These nanocomposites were prepared using different combination of solvents viz., ethanol, water, and ethylene glycol at 180 °C for 24 h. The synthesized nanocomposites were analyzed with various characterization techniques. Structural analysis indicates the formation of tetragonal phase of SnO2 for the sample prepared in ethanol, whereas for other solvent combinations, the mixture of SnO and SnO2 having tetragonal crystal structures were observed. The optical study shows enhanced absorbance in the visible region for all the prepared SnO/SnO2 nanocomposites. The observed band gap was found to be in the range of 3.0 to 3.25 eV. Microstructural determinations confirm the formation of nanostructures having spherical as well as rod-like morphology. The size of nanoparticles in ethanol-mediated solvent was found to be in the range of 5 to 7 nm. Thermogravimetric analysis indicate the weight gain around 1.3 wt% confirming the conversion of SnO to SnO2 material. The photocatalytic activity of synthesized nanocomposites was evaluated by following the aqueous methylene blue (MB) degradation. The sample prepared in ethylene glycol-mediated solvent showed highest photoactivity having apparent rate constant (Kapp) 0.62 × 10−2 min−1.

This study focused on the effect of different reaction temperature on the morphology of zinc oxide. The temperature plays a significant role for the growth along different planes and axis. We synthesized ZnO hydrothermally at different temperature (60, 100, 140, and 180 °C). The synthesized ZnO nanopowders were characterized by UV–visible spectroscopy (UV–vis), X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). The absorption spectrum of ZnO nanoparticles was observed with excitonic peaks in the range 372 to 376 nm. The XRD patterns of the particles reveal the formation of hexagonal phase for ZnO with high degree of crystallinity. The FESEM images of ZnO powder shows the formation of nanobelts, nanoplates, and nanorods. As temperature was increased, the morphology of ZnO nanostructures changed from nanobelts to nanorods. The synthesized ZnO powders were successfully employed as electrode material in dye-sensitized solar cells to evaluate the photovoltaic performances of synthesized ZnO nanobelts, nanoplates, and nanorods.