Sharif Digital Repository

Over the past several years, TiO2 has become a focus of considerable researches as it possesses unique optical, catalytic and electrical properties in different applications such as sensors, water purification and dye-sensitized solar cells (DSSC). The goal of this research was synthesis of 1-Dimentional TiO2 nanostructure with suitable properties for DSSC applications. Two different TiO2 powders including micron-size anatase and mesoporous powders (produced from reaction of TiC and HNO3) along with KOH or NaOH were employed in hydrothermal process. The process was performed in two different containers including autoclave and balloon-shaped flask. The products were characterized by X-Ray... 

The Mesoporous Titanium Dioxide film using Sol-Gel method and Evaporation-Induced Self-Assembly technique (EISA) was prepared. In this study, in order to employ the best coatings in anode electrode of dye-sensitized solar cell, different conditions of making this film, the effective parameters in final structure, and various methods of coating were analyzed. After optimizing the conditions of film creating, images of field emission scanning electron microscope (FESEM) proved the formation of a layer of mesoporous structure which thickness after three times of coating is about 1.5 micrometers. In order to increase the energy conversion efficiency of solar cells, a new formulation for... 

ZnO semiconductor has a wide band gap (3.3eV) and high electron mobility, making it a possible candidate for an effective structure-based Dye-sensitized solar cell (DSSC) semiconductor. Efficiency of DSSC based on ZnO is lower than TiO2 due to its low chemical satability. It is well known that the energy conversion efficiency of DSSC depends on the electron transport in the photoelectrode so in this investigation we fabricated high transport photoelectrode by doping Al in ZnO nanostructures. DSSC based on Al doped and undoped ZnO nanosheet synthesized by electrochemical deposition. Current density-voltage (J-V) characterizations indicate that Al-doping in ZnO crystal structure increases... 

In this research we focus on study and fabrication of one dimentianal TiO2 nanostructures and nanoheterostructures on TiO2 nanofibers in order to use them in Dye Sensitized Solar Cells (DSC). Nanofibers of titanium oxide have been fabricated using hydrothermal method. Then, hierarchical TiO2 nanostructures were grown on the nanofibers via another hydrothermal step. Increasing the effective surface of nanofibers, we achieved two secondary architectures from fibers:1-Nanoparticular fibers (TiO2 nanoparticles grown on nanofibers).2-Nanostars.After fabrication, the SEM and XRD characterizations were provided. Furthermore, the suitable pastes of these nanostructures were prepared for application... 

In this work, polyvinylidene difluoride (PVDF) as a ferroelectric polymer, polyaniline (PANI) and polypyrrole (PPy) as conductive polymer additives are used to fabricate high performance mesoporous CH3NH3PbI3-xClx mixed-halide perovskite solar cells in a sequential deposition method. Using polymer additives in perovskite precursor solution leads to modification of perovskite layer morphology by changing nucleation and growth of perovskite grains. Besides, conductive polymer additives in perovskite layer help to more charge carrier transfer. Power conversion efficiency has been enhanced from 10.40 % to 16.51% and to 13.21 % in ambient atmosphere in the presence of 1.0 wt. % of PVDF and PPy... 

Metal oxide semiconductors are promising materials for photovoltaic systems, because they are chemically stable, almost non-toxic and abundant. These materials are cheap and have low cost fabrication process. Cu2O is the most popular metal oxide semiconductor to absorb light in Photovoltaic (PV) applications, and photocathode in the photoelectrochemical systems.In this project, thermal oxide and electrodeposition methods, both interesting and cheap, were applied for preparing Cu2O films. As inexpensive materials results in low-minority carrier diffusion length, we report on surface engineering of bulk Cu2O photocathode thorough employing nanorods of copper oxide with the average lengths of... 

Solution-processed quantum dots (QDs) have attracted significant attention for the low-cost fabrication of optoelectronic devices. Here, we synthesized PbS QDs via hot injection method and passivated the trap states by using short thiols and dopant elements for photovoltaic application. In order to study the effect of dopants on photovoltaic application, PbS QDs were doped by using three different cations: Cadmium, Calcium, and Zinc. The results showed that Cd dopant has a better improvement than Ca and Zn dopants in order to increase the efficiency of the PbS QDs solar cells. We achieved solar power conversion efficiencies of 5.81% using Cd therapy. Recently, hybrid nanocomposites... 

Design hybrid systems to supply electrical energy for off grid domestic consumer in the remote villages in Iran are the main objective of this work. The hybrid systems considered in this study consist of photovoltaic array, wind turbine, battery and diesel generator. Measured wind speed data used for wind turbine energy production model. The hybrid system optimized to supply 6, 14, 20, 40 and 60 families in Bojnoord, Moorchehkhoort, Kish, Langrood, Khash and Meshkinshahr. The main purpose of optimization is to find the economic system, able to fulfill the energy requirements of a given load distribution; so Iran’s current economy and cost, considered. The optimized results for studied cities... 

Dye-sensitized solar cells (DSCs) are third generation of solar cells, which composed of a porous layer of wide band gap semiconductor such as TiO2, covered with a molecular dye that absorbs sunlight, and a counter electrode contacted by a liquid redox electrolyte. Photovoltaic performance is the collective measure of light harvesting, charge separation and charge collection efficiencies. Light harvesting has a significant role in improvement of photovoltaic performance. Molecular engineering of dyes to improve absorption spectrum or to have a broad absorption spectrum,andlight scattering layes are approaches for this porpuse. This research is focused on photon management in DSCs using... 

Dye sensitized solar cells (DSCs) are among the 3rd generation solar cells which their mechanism of light absorption is similar to chlorophyll in green leafs and is based on photo-excitation of dyes. The electron-hole pairs of photo-excited dye separate at the interface of mesoporous semiconductor-dye-electrolyte. One of the approaches to increase the light path length and therefore the light harvesting efficiency in DSC is the addition of light scatterers inside the mesoporous semiconductor (photoanode).In this research, nanoparticulated hollow TiO2 fibers are introduced as novel light scatterers in DSCs with simultaneous light scattering, light trapping and high surface area. Light... 

Dye Sensitized Solar cell (DSC) is the third class of solar cell, which consists of a nanocrystalline, mesoporous of semiconductor(The best one is Tio2), covered with a monolayer of dye molecules, platinum coated on FTO as a counter electrode and a redox electrolyte. This Photovoltaic cell which is promising low-cost materials, works on electron separation of dye molecule, and electron injection to semiconductor’s conduction photo- electrode structure and its porosity is affected the DSC’s performance. Recently, use of electrophoretic deposition (EPD) for TiO2 electrode (which best found for photo-electrode in DSC) fabrication has gained increased interests. In this method charged particles... 

In this project, The cadmium sulfide nanoparticles were formed on a nanostructured and meso-porous titanium dioxide layer and its properties were characterized. Deposition process of titanium dioxide and cadmium sulfide has been performed respectively in one stage and two stages of dipcoating. In order to probing effects of temperature and dipcoating time, samples have been prepared in various times and temperatures. Also, some of the samples have been annealed. Thickness of titanium dioxide and cadmium sulfide coatings were approximately measured 1 μm and between 3-5 μm, respectively. As expected, XRD results disclosed that cadmium sulfide and titanium dioxide were formed in the form of... 

Today usage of microwave integrated circuits in commercial and military applications is very common, especially with emerging of monolithic microwave integrated circuits that make mass production with good quality and price possible. A lot of attention are paid to designing power amplifiers used in the end of transmitter line. Because of power dispersion in transistor channels, high power amplifier causes excessive heat on the chip. Channel temperature increasing, causes operation retrogradation in circuits that result in destruction of the chip. So it is necessary to transfer this heat to the outside from the chip. It is usual to use a heatsink for this problem, however for low thermal... 

Smart grid brings miscellaneous concepts and advantages; increasing power quality, decreasing outages, motivating the consumers to participate in power system plans, and accommodating distributed generations (DG) are the most important purposes of smart grid implementation. Appearance of modern technologies makes operators devise better operation function. The effect of these technologies on the power system should be probed by sufficient criterions. In addition, preventing undesirable consequences of new technologies operation in the grid is the requirement of having smarter grid. In this thesis, based on the smart home concept two issues are discussed. In the first issue, a new algorithm... 

One-dimensional (1D) cadmium sulfide (CdS), nanostructures have significant potential applications in solar cells, photocatalysts and many electronic devices. There are many experimental approaches to synthesis 1D CdS nanostructures. Among them solvothermal method has many advantage such as controllable and inexpensive method. 1D CdS nanostructures with different properties in morphology, crystal structure, band gap energy and etc can be obtained by controlling solvothermal processing parameters. In the present work the effect of solvothermal processing parameters including reaction temperature (120ºC ,160ºC and 200ºC), process time (12h, 48h and 72h), sulfur source (S powder, Thiourea and... 

Recently, synthesis of nanostructured CdTe of II-VI semiconductors has caused much attention due to their great potential in many optoelectronic applications such as solar cells and detectors. Among different synthesis methods, solvothermal process is a suitable method due to low temperature synthesis. In this work CdTe nanoparticles, nanowires, nanorods and nanobelts with cubic structure (zincblende) were synthesized via a simple solvothermal method at a moderate temprature. The effect of processing parameters on some properties sush as crystal structure, morphology, crystallite size chemical bond configuration and optical properties of synthesized CdTe were investigated. It was found that,... 

Dye-sensitized solar cells were introduced by M. Gratzel in 1991. These solar cells have a power conversion efficiency of about 12% over the AM1.5 full sun. Traditionally, a liquid electrolyte redox system is used to regenerate the dye. Due to stability issues, a solid hole transport material has been employed to replace the liquid electrolyte as an attempt to create solid-state Dye-sensitized solar cell (ssDSC). Over past few years power conversion efficiency of ssDSCs has improved considerably and reached over 7%.
Here, ss-DSCs based on TiO2 nanoparticles as photoelctrode and P3HT as hole transport material were fabricated and characterized. We used three different methods; dip... 

Dye-sensitized solar cells (DSSCs) are emerging as low-cost alternatives to conventional, solid-state, silicon solar cells. A porous network of a nanosize semiconductor material with a wide band-gaps usually TiO2, serves as charge transport medium. A monolayer of dye is chemically adsorbed on this material. Photoexcitation of dye causes injection of electrons into the conduction band of TiO2 from where they diffuse towards a transparent conducting oxide (TCO) substrate. The dye is regenerated through receiving electrons from a redox couple dissolved in the electrolyte. After passing through a desired load, the electrons enter the cell through a counter electrode to reduce the redox ions and... 

In the present study, TiO2-reduced graphene oxide (T-RGO) nanocomposites were synthesized via various in-situ and ex-situ methods, then their photovoltaic performance was examined as photoanode and mesoporous layers in dye-sensitized Solar Cells (DSSCs) and perovskite Solar Cells (PSCs), respectively. Graphene oxide (GO) was prepared using Hummer’s method with some modifications. Both thermal and hydrothermal processes were used to reduce GO. Structural and optical characterization was analytically demonstrated by subjecting of the obtained materials by several techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, thermogravimetric analysis (TGA),...