Sharif Digital Repository

Dye-sensitized solar cells (DSSCs) have been intensively studied duringthe last decade as a promising third solar cellgeneration due to their potential low-cost manufacturingprocess. DSSCsare based on a semiconductor (i.e., TiO2), formed between a photo-sensitized anode and an electrolyte. In order to reach high conversion efficiencies, it isimportant to increase the electron injection and opticalabsorption. One promising solution to increase the electroninjection is to decrease the large band gap of TiO2 bydoping a foreign ion into TiO2 lattice.
In the present study, Ag- doped TiO2 powders and films with different Ag:Ti molar ratios are reported. The effect of dopant at.%, annealing... 

In this thesis, we focus on studying and fabrication of doped titanium dioxide electrodes and their application in nanostructured dye sensitized solar cells (DSSCs). For this purpose, non-metallic nitrogen (N) and metallic neodymium (Nd) elements were selected. N-doped titanium dioxide nanoparticles were synthesized via solvothermal method and their structural and optoelectrical properties were investigated in comparison to undoped titanium dioxide synthesized by the same method. Based on the obtained results, doping of titanium dioxide by nitrogen resulted in shifting the Fermi level up-ward, increase in charge carriers density, shift of optical absorbance to higher wavelength, and decrease... 

Hole-transporter-free perovskite solar cells with structure of TiO2/ZrO2/C triple-layer scaffold filled with perovskite are great alternative to the conventional ones due to the possibility of making full printable low-cost and stable devices. In the present work, the impacts of the structures of the quadruple layer scaffold in the form of TiO2/ZrO2/NiO/C and triple layer scaffold in the form of TiO2/ZrO2/C on their photovoltaic performance are studied. In addition, the effects of thickness and deposition method of each layer were investigated as well as the effect of compounding of the carbon counter electrode. All devices were constructed by a simple printable method. Electrochemical... 

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... 

Perovskite solar cells are the new generation of solar cells, and are mainly introduced in two types of structures.1) planer and 2) mesoscopic structure. The difference between these two structures derives from the absence of mesoporous layer in the planer structures. The mesoporous layer acts as an electron transporting layer, and is mainly a titanium dioxide semiconductor. To apply the mesoporous layer, the preparation of the TiO2 paste is needed.The synthesis of titanium dioxide nanopowder for the preparation of TiO2 paste requires high temperature heat treatment and is not desirable in terms of energy consumption.Another weakness of this layer is the presence of surface defects, which... 

Solar cells, as a part of photovoltaics (PV) industry, have a significant share in the renewable energy market. Perovskite solar cells (PSCs) and thin film solar cells (TFSCs) achieved 23% and 22% power conversion efficiencies (PCEs) respectively. However, the PV industry still faces challenges like “high manufacturing costs” and “stability”. Among the strategies to overcome these challenges are substitution of the costly materials with cheaper, more abundant ingredients along with utilizing inexpensive deposition methods like printing rather than vacuum-based methods such as evaporation and sputtering. Carbon materials attract more attention in the solar cell research community for their... 

In recent years, much attention has been focused on quantum dot films due to their high amount of surface area and their size-dependant band-gap tenability. However, high surface area results in increase in energy traps in case of insufficient surface passivation. In this research, PbS colloidal quantum dots were synthesized via hot injection route having the size of 3 nm approximately. Then cationic doping with Zn, Ca and Cd and ligand exchange of long oleic acid with short organic mercaptopionic acid were done. Excitonic peak of these dots and photoluminescence peak appeard in wavelengths of 930 and 1100 nm respectively. Optimum film thickness was also determined as 300 nm. Quantum dot... 

In this research we focus on fabrication and characterization of Dye and Cadmium based Quantum Dot Sensitized Solar Cells (QDSCs) based on TiO2 nanostructures. TiO2 nanorods were synthesized with a simple chemical method. TiO2 nanorods, TiO2 nanorod/TiO2 and ZnO nanoparticle composite structures were integrated as photoanode in dye sensitized solar cells (DSSCs). Incorporation of TiO2 nanoparticles into the bare nanorods increased the efficiency more than 45%. Monitoring electron transport properties of the cells, pointed out the crucial role of electronic structure of composite film components on the performance of cells. Suitable morphology of TiO2 nanorods, led us to use them, to make a... 

Thin film solar cells have low efficiency compared to crystalline silicon solar cells; however, they are low-cost and flexible. In manufacturing these solar cells, thin films are deposited at high temperatures (higher than 200℃) on a thick metal, plastic, or glass substrate using sputtering and plasma enhanced chemical vapor deposition (PECVD) methods. Since the thin films and substrate have different thermal expansion coefficients, cooling the system from deposition temperature to room temperature induces thermal residual stresses in both the films and substrate. In addition, these stresses, especially those induced in the amorphous silicon layer can change the carrier mobility and band gap... 

Different structures of TiO2 photoelectrodes were fabricated with different structures and arrangement modes of the layers. TiO2 Nanoparticles were synthesized by solvothermal method and the effect of solvothermal processing parameters on morphology and crystal structure of nanoparticles was studied. Hierarchical and spherical TiO2 particles were synthesized to use in photoanode electrode as light scattering particles. FE-SEM and XRD analyses revealed that TiO2 nanoparticles had uniform and nanometer grains with particle size around 20nm and average crystallite size of 4nm. The optical properties of TiO2 particles were studied through UV–Vis absorption and DRS analysis. The indirect optical... 

With high power conversion efficiency, comparable to silicon solar cells, the conventional perovskite solar cells (PSCs) are leading the photovoltaic research scene. However, they have poor stability in operation due to instability of organic-inorganic hybrid PSCs. Several methods have been proposed to improve their stability including Substitution of the organic component by an inorganic one For example, inorganic perovskite compound such as 〖 CsPbI〗_3 with bandgap about 1.7 eV is a good candidate. However, it requires high synthesis temperature (about 300 ℃), and the resulting cell has a lower efficiency than the organic one. Introduction of Cs, as an inorganic element, into organic... 

This thesis deals with a theoretical and experimental investigation of different approaches for reduction of electronic recombination in the semiconductor/Dye interface of dye sensitized solar cells (DSSC) including dye coverage, core-shell structures and energy level distributions. Interface of ZnO/TiO2 in the core-shell structure have been studied by density functional theory and the energy level distribution of surface atoms, recombination and Fermi level changes, open circuit voltage and surface dipole distributions have been discussed.
The presence of TiO2 shell increases the ZnO surface dipole moment, and shifts the ZnO conduction and valence bands to higher energies. Also, it... 

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 thesis, pure –known as T- and chromium doped titanium dioxide nanoparticles –known as -CTx- with different dopant atomic ratio (0.1 to 5 %at.) were synthesized using a facile, fast and efficient method. FESEM and XRD studies showed no morphologic and structural change via Cr doping of nanoparticles (size in the range of 20-30 nm). However, according to DRS analysis, Cr intrusion in TiO2 crystal structure, drastically reduced band gap energy of pure TiO2 from 3.14 eV to 1.81 eV for CT3 powder and improved absorption range of UV-Vis spectrum. Mott-Schottky plots indicated that, Cr doping, caused reduction in donor density of TiO2 and an upward shift in the conduction band edge.... 

A new strategy for enhancing the efficiency of TiO2 dye sensitized solar cells (DSSCs) doped with Ni ions with different molar percentages (i.e., 0, 0.5, 1, 5 and 10 mol%) was reported. The samples were prepared by sol-gel route and characterized by means of XRD, DRS, UV-visible, FESEM and photovoltaic measurment techniques. It was found that Ni-doped TiO2 nanoparticles had a mixture of anatase, rutile and brookite crystal structures. Moreover, the band gap energy was decreased with increasing Ni molar ratio, The highest cell efficiency of 5.4% was achieved for 1mol% Ni-doped TiO2, being 42% greater than that of pure TiO2 nanoparticles  

The purpose of this study is the fabrication and characterization of ZnO nano particles and the application of ZnO in solar cells. Therefore, firstly we fabricate the high stable solution of ZnO nano particles and then characterize ZnO nano particles. In addition, we study sulfurzation and selenization of zinc oxide thin films. We use ZnO nano particles for fabrication of transparent conductive films. Transparent conductive films have many applications such as touch panels, displays and solar cells. The most applicable transparent conductive electrode is indium tin oxide , which is the most expensive layer in solar cells. But silver nanowires has some challenges such as high surface... 

In recent years, the use of thin film solar cells has been widely considered due to the ability of their solution-based coatings. One of these is the chalcopytie solar cell copper indium gallium di-selenide (CIGS). The absorber layer of copper indium gallium diselenide was carried out by a spray pyrolysis method. then by using a chemical bath deposition, a buffer layer was fabricated to form the p-n junction. Subsequently, silver nanoparticles and zinc oxide alumina sputtering were used to form a transparent conductive film. with using the substrate Molybdenum and by optimizing the test conditions, such as temprature and deposition time to adjust thickness of layers, Cell with an... 

In this research, we focus on study and investigation of the role of Tin(IV) Sulfide (SnS2) nanostructured layer as electron transport layer in perovskite and chalcogenide thin film solar cells. For this purpose, SnS2 powder was prepared through hydro/solvo-thermal method, utilizing different ratios of water and ethanol as solvent and various sulfur sources (thioacetamide and thiourea). Afterwards, different solvents were investigated to achieve a stable ink (about one month) with uniform dispersion. After determining the appropriate ink and powder, thin films of SnS2 were prepared employing spin coating, spray pirolysis and laser pulsed deposition (PLD) methods and characterized. With each... 

Luminescence down shifting (LDS) of the incident spectrum is a practical strategy that helps to increase the light harvesting efficiency by manipulating the incident spectrum instead of interfering with the active material inside the cell. In this research, for a dye-sensitized solar cell with a near-infrared sensitizer, the photovoltaic performance was enhanced remarkably with a reflective luminescent down-shifting (R-LDS) layer. Different inorganic phosphors with different luminescent quantum efficiencies have been used as the down shifting materials to increase the light-harvesting efficiency of DSSCs sensitized with TT1 and SQ1 dyes. Four different structures were examined to find the... 

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...