Haihong Niu

Influence of deposition strategies on CdSe quantum dot-sensitized solar cells: a comparison between successive ionic layer adsorption and reaction and chemical bath deposition

Deposition and synthesis strategies of quantum dots (QDs) exert appreciable influences on the photovoltaic properties of quantum dot-sensitized solar cells (QDSCs). In this paper, a systematic characterization of morphology, optical and electrochemical properties has been carried out to correlate the assembling of QDs with the performance of the resultant QDSCs. CdSe sensitized TiO2 solar cells were investigated focusing on the influences of two commonly used in situ QD deposition methods, i.e., successive ionic layer adsorption and reaction (SILAR) and chemical bath deposition (CBD). By applying a pre-assembled CdS seed layer prior to CdSe deposition, a power conversion efficiency up to 4.85% has been achieved for CdS/CBD-CdSe cells, which is appreciably higher than 3.89% for the CdS/SILAR-CdSe cell. TEM images revealed that CdS seeded SILAR is only capable of less than full coverage, in contrast, the CdS seeded CBD technique secures full conformal coverage of QDs on TiO2. The full conformal coverage of QDs offers two benefits, (1) high loading of QDs for efficient photon capturing, contributing to the increase of photocurrent, and (2) suppression of interfacial charge recombination, resulting in high open-circuit voltage and a large fill factor. Our success in achieving the perfect coverage of QDs based on CdS seeded CBD highlights strong implications for the performance optimization of QDSCs.

Dye-sensitized solar cells based on flower-shaped α-Fe2O3 as a photoanode and reduced graphene oxide–polyaniline composite as a counter electrode

We demonstrated an environmentally friendly photoanode composed of nano-flower structured hematite (α-Fe2O3) and a photocathode composite made of reduced graphene oxide–polyaniline (PANI-RGO) for efficient dye-sensitized solar cells (DSSCs). The porous petals–root structure of the α-Fe2O3 film characterized by different structural means (XRD, SEM, HRTEM, SAED and N2 adsorption–desorption) was demonstrated to provide an efficient pathway for the charge carrier transfer of DSSCs. The incident photon-to-electron conversion efficiency (IPCE) profiles suggested a broad photo-response spectral region of up to 700 nm in the presence of nano-flower α-Fe2O3 in the photoanode. The PANI-RGO composite coated on the counter electrode was proven to have a higher photon-to-electron conversion efficiency than the conventional Pt, which is attributed to the improved electro-catalytic activity and conductivity of PANI-RGO. It was found that the energy conversion efficiency (1.24%) achieved from PANI-RGO as photocathode material is increased by a factor of 1.3 compared with Pt. The better electro-catalytic activity of PANI-RGO CE is brought about by a synergistic effect between PANI and RGO, which was verified by micro-Raman spectroscopy and electrochemical characterizations (CV, EIS).

Dye-sensitized solar cells with 3D flower-like α-Fe2O3-decorated reduced graphenes oxide as photoanodes

For the first time, we report a one-step fabrication of an environment-friendly approach to synthesize flower-like α-Fe2O3 hierarchical nanoparticles (NPs)/reduced graphene oxide (RGO) hybrids by combining the graphene oxide (GO) with the growth of α-Fe2O3 NPs. The GO sheet which possesses the functional group, such as hydroxyl (–OH) and carbonyl groups (–OOH), can be easily incorporated with the petal of the flower-like α-Fe2O3 in ethanol and water solution through a solvothermal process, during which GO is reduced to RGO without the addition of any strong reducing agent or requiring any post-high-temperature annealing process. The as-prepared samples are loose and porous with flower-like structure, and the RGO hybrids were wrapped up uniformly on the sheet of α-Fe2O3 NPs. To demonstrate the potential applications, we have fabricated dye-sensitized solar cells (DSSCs) from the as-synthesized hierarchical flower-like α-Fe2O3/RGO and investigated it for the photoanode of DSSCs. Results show that the hierarchical α-Fe2O3/RGO solar cell exhibits improved performances in comparison with the free α-Fe2O3 NPs. The enhancement of photovoltaic properties is attributed to the unique porous nature and good conductivity which allow more efficient diffusion of I− ions and facilitate the transfer of electron in the network.

Hydrothermal Growth of Aligned ZnO Nanorods along the Seeds Prepared by Magnetron Sputtering and its Applications in Quantum Dots Sensitized Photovoltaic Cells

Hydrothermal Growth of Aligned ZnO Nanorods along the Seeds Prepared by Magnetron Sputtering and its Applications in Quantum Dots Sensitized Photovoltaic Cells Well-aligned ZnO nanorods were grown on a conductive substrate via a hydrothermal route. The substrates were pre-seeded with ZnO by a technique of radio frequency (RF) magnetron sputtering. The influences of sputtering power, annealing treatment, and the size of seeds on the morphologies of the final-prepared ZnO nanorods have been studied. It was found that the length and the aspect ratio of the ZnO rods can be readily tuned by control of the ZnO seeds which results from the RF sputtering experiments. ZnO seeds deposited at low sputtering power (100~125 W) share uniform size distribution with smaller average size (~30 nm). Higher sputtering power yields longer ZnO rods with a higher aspect ratio up to ~12.5. The seed layers after annealing (~500oC) produce ZnO rods with an increased average diameter and a smaller aspect ratio, and these features benefit the electron transfer when the prepared ZnO nano-arrays are used as electrode substrates in photovoltaic cells. By deposition of hydrophilic CdSe quantum dots (QDs) on the ZnO nano-rod, the maximum photo to current efficiency (0.42%) was obtained in case of ZnO nanorod with the length of ~2.75 μm and an aspect ratio of ~9.5 obtained from the seeds after annealing.

Preparation of CdSe Quantum Dot Sensitized Solar Cells Based on Improved Successive Ionic Layer Absorption and Reaction Method

Preparation of CdSe Quantum Dot Sensitized Solar Cells Based on Improved Successive Ionic Layer Absorption and Reaction Method Particles of metals or other materials in nanometre size are called as nanoparticles (NPs). Of ten endophytic fungi screened, seven endophytic fungi namely Alternaria alternata, Botryodiplodia sp., Pestalotia sp., Fusarium sp., Aspergillus sp. Aschersonia sp. and Phomopsis sp. were able to synthesize silver nanoparticles. Silver metal nanopartites were synthesised successfully by both mycelium as well as cell filtrate of Pestalotia sp., which was initially observed by spectrometric analysis. TEM pictures revealed the synthesis of angular shape of silver nanoparticles like trigonal, pentagonal, hexagonal, few of cuboids and some were of spherical in shape too. Most of nanoparticles (76%) were found below the size of 40 nm. FTIR spectra peaks showed the presence of -NH, CO, C=C and C-H containing organic metabolites which might play a role in stabilizing the nanoparticles. Silver nanoparticles solution (0.5 mM) inhibited the growth significantly than control against all pathogenic bacteria tested. Mycosynthesized AgNPs were most active against Aeromonas hydrophila @2 μg/ml IC50 followed by Staphylococcus aureus (6 μg/ml), Escherichia coli (8μg/ml), Morganella morganii (24 μg/ml), Salmonella typhi (42 μg/ml), Enterococcus faecalis (40 μg/ml) and Klebsiella pneumoniae (50 μg/ml) respectively. Silver nanoparticles had also shown antioxidant activity with DPPH free radical scavenging with inhibitory concentration (IC50) at 47 μg /ml. To combat with new emerging pathogenic bacteria that threat our society by causing dreadful diseases, we require the development of effective therapeutics. Thus, eco-friendly synthesised antimicrobial and antioxidant silver nanoparticles allow us to suitably employing their application in nanoparticles mediated drug delivery and therapy of diseases.