Sharif Digital Repository

This research is focused on fabrication of TiO2 layers by electrophoretic deposition (EPD) for application as photoanode in Dye Sensitized Solar Cell (DSC). DSCs are third generation of solar cells, also known as the Grätzel cell, after its inventor Michael Grätzel. A DSC is composed of a porous layer of wide band gap semiconductor such as TiO2 and ZnO, covered with a molecular dye that absorbs sunlight, and a counter electrode contacted by a liquid redox electrolyte. Dye Sensitized semiconductor (photoanode) has important role in conversion of photon to electricity. To achieve higher efficiency, preparation of photoanode with high surface area resulted to enough dye adsorption is necessary.... 

Counter electrode of dye sensitized solar cell is prepared by deposition of a thin catalytic layer onto a conducting substrate and is responsible for reduction of iodide/triiodide redox electrolyte. Conventionally, counter electrode is made of platinum.
Depending on the method of deposition, the thickness of Pt layer varies. The Pt layer may be so thick that it acts as reflector and returns the incident light back to the cell. In this case, large amount of Pt is used and a rise in cost is been made, but only the Pt particles in the interface of counter electrode/electrolyte take part in the reduction reaction.
The aim of this project is optimization of making a counter electrode,... 

Increasing of human demanding for energy and limiting of fossil fuels and bio-logical problems, it seems necessary to access new and clean source of ener-gy. For instance, one of these sources of energy is sun. If we can impart from this infinite energy source so health and natural life can be pictured for human. Nanostructure dye sensitized solar cells in compare with other photovoltaic cells are more economical and practical as a result of lower material cost and simpler manufacturing process. In general, a typical dye sensitized solar cell is a sandwich structure based on two transparent conducting oxide (FTO) glasses. The FTO glass substrates are expensive and account for most of... 

“Progress” is among most frequently used terms in the past few centuries in public discussions, scientific communities as well as economic and sociopolitical policy making. This term has been used in our daily conversations so frequently that it seems to become an intrinsic goal for human beings. However, even a short survey of the introduced meanings of and suggested approaches to achieve “progress” during the last four centuries - since the term was first used- demonstrates that we are faced with a multitude of views from the different - and sometimes contradictory - schools of thoughts. Unfortunately, in recent decades, despite our national desire to “progress”, we have not yet thought... 

In this project single sided dye sensitized solar cell is introduced as a new design that has both of electrodes in one side. These electrodes can be separated vertically by a thin insulator layer such as SiO2 or horizontally by lithographic method. First a metallic thin film is patterned by lithography, and then thickened by electrochemical deposition of Chromium. Platinum is electrodeposited on the substrate of counter electrode and a thin spacer layer is deposited on Platinum layer to separate it from Titanium dioxide layer.
In Chapters 1, 2 & 3 basic science and methods which are needed for doing this project is introduced. In chapter 1 material for making a standard dye sensitized... 

The efficiencies of perovskite solar cells have increased rapidly in recent years and reached about 22%. Which hopes to make this type of solar cell more functional. In the normal structure of perovskite solar cells, the presence of mesoporous TiO2 mesoporous layer has increased sustainability and efficiency. To create this layer, a common method is placing the sample in a furnace for 30 minutes at 450°C-500°C. Using the furnace, in addition to being time consuming, has a high energy consumption. In this study, we tried to create a TiO2 mesoporous layer with the help of lighting. To create TiO2 mesoporous layer, What causes porosity in the layer is the removal of ethyl cellulose and create... 

During recent years, thin-film solar cells based on chalcogenide light absorbers with CuInxGa1-xS(Se)2 compound have attracted considerable attraction due to their desirable band gaps and demonstrated high power conversion efficiencies. These solar cells are fabricated under two categories named as ‘substrate’ and ‘superstrate’, generally. The best reported energy conversion efficiency belongs to substrate type (sodalime glass/Mo/absorber layer/buffer layer/window layer) CIGS solar cells, most have been fabricated with vacuum processes. In spite of this, superstrate solar cells (transparent conducting oxide/blocking layer/buffer layer/absorber layer/back contact) provide easier and cheaper... 

In this research, we study and optimize the inverted perovskite solar cells (PSCs) using nano layers of NiOx and Li:NiOx as hole transporting layers (HTLs) and nano layers of PC70BM and C60 as electron transporting layers (ETLs). We fabricated inverted PSCs with three different HTLs, namely MoOx, PEDOT:PSS and NiOx, using vapor assisted solution processed (VASP) method for making MAPbI3 perovskite which yielded a power conversion efficiency (PCE) of 1%, 1.93% and 3.65%, respectively. Solution-processed deposition method, high transparency (˃90%) and high band gap (3.9 eV) are the most advantages to use NiOx as HTL in current research. Using lithium as dopant to the NiOx increases the... 

UF membranes are widely used in various industries now, a major type of these membranes are ceramic membranes which are resistant to high temperatures and corrosive fluids. In this thesis we developed an anisotropic UF ceramic membrane based on 20nm TiO2 nanoparticles on a prous sustrate. We had two major challenges, the first one was to find a suitable prous substrate and the second one was to find an appropriate coating method. Our main task was to optimise the process conditions to achive a crackless and uniform membrane layer with minimal ups and downs. Lots of coating methods and TiO2 inks have been tried, finally we used a coating method which we called it “Soft Blade Coating”, with... 

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... 

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... 

Titanium dioxide has covered a wide range of applications as a semiconductor photocatalyst. TiO2 is an indirect, 3.2 eV band gap semiconductor which can be stimulated using UV light. Improving the quick electron-hole recombination rate, we can enhance the photocatalytic efficiency of this semiconductor. One of the approaches in hand is to use noble metals in connection to TiO2. Among noble metals, due to its plasmonic and anti-bacterial properties and ease of preparation, silver would serve as a perfect candidate. The mechanism for photocatalytic enhancement in Ag-TiO2 structures lies behind the fact that silver can trap the photogenerated electron of TiO2 and inhibit the electron-hole... 

The optimization of CdS photoluminescence nanoparticles which has been considered as one of the most important II-VI semiconductors has been studied here. As the first step, synthesis parameters effect on CdS:Mn photoluminescence intensity has been regarded by thermochemical method. Effect of parameters like pH solution, heating time and capping agent concentration on photoluminescence of these materials has been experimented. What seemed so important was reaching nanoparticles with suitable nano size and nano structure and having highly photoluminescence intensity. Observing the good effect of Oxygen on photoluminescence of CdS nanoparticles leaded us to concentrate on synthesizing CdS:O... 

Semiconductor nanocrystals act as a good luminescent layer in new coming electroluminescence devices. Research on luminescent devices based on nanocrystals such as silicon nanoparticles, has been progressed over the last decades. In this research, silicon nanoparticles have been synthesized from porous silicon layer that was created through an electrochemical process. The effective luminescent parameters like electrolyte contents, current density and reaction time have been investigated. The maximum luminescence has been captured when the current density and reaction time were adjusted at 30 and 20 min, respectively. In addition, volume ratio Ethanol:HF 14:8 was another modified... 

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 this research, we fabricated and characterized hybrid organic-inorganic perovskite solar. The purpose of this study was the fabrication of multi-cationic perovskite films with vapor-assisted solution process, which was carried out in two different atmospheric and low-pressure conditions. In this regard, the reference cells with CH3NH3PbI3 and HC(NH2)2PbI3 compositions were made, which yielded 15.2% and 7.19% efficiencies in atmospheric conditions, and 6.38% and 2.65% in low pressure conditions, respectively. To increase the stability and to improve cell device performance, Br anion was added to the CH3NH3PbI3 structure. In optimum conditions, the conversion efficiency was 12.18%. Further... 

Finding a reliable and reproducible method to deposit thin films of semiconductors is a huge leap forward in order to fabricate nano-structured solar cells. As the third and forth generation of solar cells are based on semiconductors which are soluble in solvents and can be deposited with solution-based methods, finding a proper printing mechanics can lead to cheap solar panels. In this thesis we have designed and fabricated an apparatus to deposit lead iodide films. These thin films can be used to fabricate perovskite solar cells which are based on methylammonium lead iodide perovskite. We have also investigated different inks consisting of different additives and solvents best suited for... 

The highest efficiency of Perovskite solar cells that is attained up to now, is around 24%. This champion solar cell is prepared under vacuum. This method suffers from low rapidity, small deposition area and high cost which are not compatible with commercialization. Printing method has a special position in mass production of electronic equipment, such as solar cells. This method has the potential of high rapid, low cast and repeatable deposition. In this thesis, I introduce a novel deposition method, named Capillary Adhesion Coating, which is based on capillary concept. The novel deposition method coats infinite perfect thinfilms with high rapidity and low cost. After the introducing of... 

According to Iran's proper location to take advantage of solar energy and the ability of nanostructured solar cells fabrication in the country, in this study, the manufacturing problems and complexities of nanostructured solar cells such as dye solar cells and perovskite-based solar cells are investigated. The chromium metal as an alternative to the transparent conductive substrates in order to reduce the manufacturing cost of dye solar cells (DSCs) and reducing series resistance is introduced in this study. In case of utilizing chromium as a substrate for photoanode, the thickness of CrxOy layer is controlled by depositing TiO2 compact layer and the efficiency of DSC is increased from 2.6%... 

By the use of flexible substrates like metal foils and meshes and plastic ones, fabrication of flexible dye sensitized solar cells are possible. Flexible dye sensitized solar cell, not only is utilized in portable, light electronic devices, but is also conductive to industrial roll to roll fabrication which enables the implementation of high throughput production lines and its associated potential reduction in manufacturing costs. This thesis has concentrated on fabrication of flexible dye sensitized solar cells by use of stainless steel mesh as substrate of photo-anode, because of its satisfying stability in electrolyte, flexibility, transparency and low cost. In this research, an efficient...