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A core-shell nano-heterostructured perovskite BiFO3@nitrogen doped mesoporous TiO2 (BFO/n-TiO2) hydrothermally assembled via using citric acid and polyethlene glycol (PEG) was characterized through XRD, TEM, FTIR, UV–Vis diffuse reflectance, IPCE, N2 adsorption and impedance spectroscopy. It has been demonstrated that the photovoltaic yield of the 90%N-TiO2-10%BFO electrode achieves a power conversion efficiency (PCE) of 4.5%, which is 1.85, 2.5, 3 and 1202 times higher than those of 10%N-TiO2-90%BFO, 50%N-TiO2-50%BFO, n-TiO2 and pristine BFO, respectively. It is acknowledged that the former electrode exhibits a significant visible light harvesting capability, lowest band gap (Eg = 2.0 eV) as well as the highest IPCE% (36% at 460 nm) values. The EIS and capacitance results illustrated that 90%N-TiO2-10%BFO owns excessive charge carriers (e− − h+); compared to rest of nanocomposites, with a great sparation, to assist boosting the PCE value. This was highly aided by the surface defects seen on the core represented by BFO, which worked as a rational carrier trapper between the N719 dye and the n-TiO2 shell structure. The surface texturing properties of the nanocomposite forming the 90%N-TiO2-10%BFO electrode including SBET (Asahi et al., 2001) and pore volume (0.48 cm3 g−1) have shared significantly in improving the conversion efficiency of such p-n heterojunction based solar cells; which never achieved as such in all BFO-based solar cell devices, with acceptable tunability. Keywords: BFO/n-TiO2, Core-shell structure, DSSC, Charge transfer, Heterojunction p-n, Surface defects

Nanocomposites of hexagonal ZnO nanorods incorporated into carbon nanotube-graphene (ZnO/CNT-GO) were prepared using a simple hydrothermal approach. The structure, light absorption, surface texturing, and morphology characterizations have established the strong interaction between ZnO, carbon nanotubes, and graphene oxide components because of the presence of well-dispersed ZnO nanorods with an aspect ratio of 3.4 (L × D = 75 × 22 nm). The assembled dye-sensitized solar cell of a ZnO/CNT-GO photoanode exhibited a superior performance, with a power conversion efficiency of 7.73%, surpassing those of its ZnO/CNT (5.07%) and ZnO/GO (3.96%) counterparts. Although CNT-GO exhibited a higher incident photon-to-current conversion efficiency (IPCE) and lower photoluminescence (PL) intensity than those of the ZnO/CNT-GO composite, it presented a lower conversion efficiency of 5.60%. This can be attributed to the presence of structural defects at the CNT/GO interface, which resulted in lower electronic conductivity (0.25 × 10−3 Ω−1 cm−1 vs. 0.8 × 10−3 Ω−1 cm−1 for ZnO/CNT-GO) and optical performance. The ZnO/CNT-GO composite showed a superior Isc value of 17.6 mA/cm2 but a lower Voc value of 0.63 V in comparison to those of its ZnO/GO analog (3.9 mA/cm2, 0.8 V); it also showed a manifested increase in surface area and pore radius values (227.5 m2/g, 58.9 A) toward the dye absorption. The electrochemical capacitance performance obtained via using charge-discharge and impedance spectroscopy revealed an excellent specific capacitance in the order of ZnO/CNT-G (290 F/g) > CNT-G (275 F/g) > ZnO/G (230 F/g) > ZnO/CNT (183 F/g) at 1.0 A g−1. This is attributed to the synergistic effect of ZnO within the CNT/GO nanocomposite and affirms its charge collection efficiency toward the improvement of dye-sensitized solar cells. The formation of a p/n junction between CNT/G and ZnO nanorods, as evidenced by the Mott-Schottky analysis, played a vital role in the improvement of solar cell devices based on the narrowing of the band gap (Eg = 2.64 eV), ease of electronic transfer, transient photocurrent density, as well as framework mesoporosity.

Ag@Ag2O/RGO nanocomposites with different loads of Ag (0.4%–8.5%) were synthesized using a simple deposition method in the presence of a triblock copolymer template at different annealing temperatures (250 °C and 400 °C). All samples were characterized with various techniques such as XRD, FTIR, Raman, TEM-SAED, N2 sorptiometry and UV-Vis diffuse reflectance. The supercapacitor performance of the samples was measured. Besides, the catalytic performances of the samples towards 4-nitrophenol (4-NP) reduction were tested under dark conditions. The results revealed the well dispersion of Ag and Ag2O moieties on RGO with crystallite size in the range of 17–34 nm. The nanocomposite Ag@Ag2O/RGO annealed at 400 °C exhibited the highest reduction rate constant for 4-NP reduction (0.01 s−1). In addition, this composite has shown the highest specific capacitance of 312 F g−1 at scan rate of 20 mV s−1 and 119 F g−1 at a current density of 11 mA g−1.

Spherical TiO2 particles (60 nm) were obtained by using a Triton X-100. The surfactant was employed in two stages, i.e., in the hydrolysis of TiCl4 and then in the precipitation of the corresponding Ti (IV) polymers. The advantages of such spherical TiO2 particles were examined in terms of photovoltaic characteristics of a dye-sensitized solar cell (DSSC) using Orange IV dye as sensitizer. Significantly higher overall solar energy conversion efficiency was obtained for a DSSC using the film of these spherical TiO2 particles, compared with that of a cell using a TiO2 film prepared without surfactant.

Silica and montmorillonite-supported silica nanoparticles were prepared via an acid one step sol-gel process. The synthesized solids were characterized using XRD, FTIR, TEM and N2 adsorption. The effect of preparing temperatures on the structure and properties of the silica nanoparticles were studied. The results show that the increase of annealing temperature from 25 to 200℃, don’t change amorphous state of silica. While for montmorillonite-supported silica the clay platelets are delaminated during the sol-gel process. TEM results showed that the average particle size of silica is increased by increasing temperature due to the particle sintering and the clay-silica nanoparticles possessed core–shell morphology with diameter of 29 nm. The surface area measurements showed that by increasing annealing temperature the surface area was decreased due to aggregation of particle. The clay-silica sample showed lower average pore width than that of the silica prepared at 200℃ indicating that it has a macropores structure. The adsorption efficiency of the prepared samples was tested by adsorption of protoporphyrin IX. The highest adsorption efficiency was found for SiO2 prepared at 200℃. Temkin model describe the equilibrium of adsorption of protoporphyrin IX on caly-silica nanoparticles under different conditions.

Polyaniline/silver (PANI/Ag) nanocomposite was prepared by chemical oxidative polymerization of aniline monomer in the presence of nitric acid. The formation of PANI/Ag nanocomposite was characterized by XRD, FTIR, TEM, UV-vis spectroscopy. The XRD patterns indicated that the crystalline phase of Ag is cubic with crystallite size of 93 nm. The TEM image shows that the Ag nanoparticles are well dispersed in the polyaniline matrix. Optical measurements show that the value of optical band gap of nanocomposite is lower than that of pure PANI. The DC-, AC-conductivities, dielectric permittivity (e') and dielectric loss (e'') of (PANI/Ag) nanocomposite and pure PANI have been measured in the temperature range from 303 to 723 K and frequency range from 10 to 103 kHz. The electrical conductivity of the (PANI/Ag) nanocomposite is higher than pure PANI. Temperature variation of frequency exponents in this blend suggests that AC-conductivity is attributed to correlated barrier hopping mechanism. At all frequencies, the e' value for (PANI/Ag) nanocomposite is higher than that for pure one. The higher dielectric constant of the PANI/Ag nanocomposite indicates their better ability to store electric potential energy under the influence of alternative electric field.

ZnO and Fe2O3 nanoparticles have been formed in a silica matrix, through the sol–gel method and were used as a photoanode to fabricate dye-sensitized solar cells (DSCs). The obtained oxides were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscope and UV–visible absorption spectroscopy. The results indicate that ZnO and Fe2O3 prepared by this method may be used as photoanodes in photo-electro-chemical energy conversion systems. DSSCs have been built using eosin Y as photosensitizer and their photocurrent, open-circuit voltage, fill factor and efficiency have been measured under direct sunlight illumination (1000 Wcm−2). A ZnO-film solar cell had the best performance with an open-circuit voltage of Voc=0.7 V and short-circuit current density of Isc=490 μA/cm2. This was attributed to high optical gap energy and transparency of ZnO compared to Fe2O3. The effects of annealing temperature and concentration of Fe2O3 on conversion efficiency of the Fe2O3 based solar cell were also studied.

Nanocrystalline SnO2 thin film was prepared by cathodic electrodeposition–anodic oxidation and its structure was characterized by X-ray diffraction, SEM, UV–visible absorption and nitrogen adsorption–desorption by BET method. The obtained film has a surface area of 137.9 m2/g with grain sized of 24 nm. Thus the prepared SnO2 thin film can be applied as an electrode in dye-sensitized solar cell. The SnO2 electrode was successfully sensitized by Erythrosin dye and photoelectrochemical measurements indicate that the cell present short-circuit photocurrent (Jsc) of 760 μA/cm2, fill factor (FF = 0.4), photovoltage (Voc = 0.21 V) and overall conversion efficiency (η) of 0.06% under direct sun light illumination. The relatively low fill factor and photovoltage are attributed to the reduction of triodiode by conduction band electrons and intrinsic properties of SnO2.

We have developed dye-sensitized nanocrystalline CdS and ZnS solar cells (DSSCs) based on crystal violet, methylene blue, and fluorescein photosensitizers. Nanocrystalline CdS and ZnS were synthesized by a green synthesis method using starch as the capping agent. Characterization of nanocrystalline CdS and ZnS was carried out by optical absorption and x-ray diffraction. The results indicate that CdS and ZnS prepared by this method may be used as photoelectodes in photo-electro-chemical energy conversion systems. DSSCs have been built and their photocurrent, open-circuit voltage, fill factor, and efficiency have been measured under direct sunlight illumination (1000 Wcm−2). The efficiency of the cells made from dye-CdS was much higher than that of the cells made from dye-ZnS. This can be attributed to the particle size effect. Among the prepared dye-sensitized solar cells, a DSSC based on fluorescein dye as the photosensitizer produced the highest overall light solar energy to electricity conversion efficiency.