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In this research, CaMnO₃ powders have been synthesized by solid state reaction and sol-gel methods at calcination temperature of 800°C. Particle size and morphology of the calcined powders have been investigated using XRD and TEM techniques. TEM image showed that the average particle size of the samples, prepared by sol-gel method, is about 85 nm. The optical gap was measured using the absorption spectrum of the powders. The value of the band gap was found for the sample synthesized by sol-gel method is about  3.46eV and that  for sample prepared by solid solution to be about 3.40eV. Also the phase formation of the powders has been studied by Fourier transform infrared (FTIR) spectroscopy. Resistivity measurements of the samples between 300-550°K revealed that resistivity of the samples decreases with increasing temperature.

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Organic-inorganic perovskite (CH₃NH₃PbI₃), due to an appropriate energy gap to absorb sunlight, is used as an absorbent layer in third generation solar cells. Crystallinity of light absorbing layer plays an important role in the performance of perovskite solar cells and substrate plays an important role on crystallinity of light absorbing layer. In superstructure solar cells, alumina (aluminum oxide) is used as the substrate of light absorbing layer. In this paper, alpha and gamma aluminum oxide are used as the substrate of perovskite layer. The effect of this work on the crystallinity of perovskite layer and parameters that affect the performance of solar cells have been investigated. It was found that by taking into account all the parameters that affect the performance of solar cells, alpha phase aluminum oxide to the gamma phase is more suitable for use in perovskite solar cells that fabricated by two step deposition.

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The CH₃NH₃PbI₃ is one of the most widely used and famous lead halide perovskite absorber layer for using in perovskite solar cells. One of the ways to deal with the instability problem of this perovskite structure in environmental condition is bromide doping in this composition. In this work, the structural and optical properties of the bromide doped CH₃NH₃PbI₃ absorber layers were studied as well as J-V characteristics of solar cell devices based on this absorber layer were also measured and analyzed. Photovoltaic parameters of the fabricated solar cell were measured continuously for 162 days. The results of this study showed that even though the bromide-free perovskite devices has the highest PCE (11.65%), but suffer from a significant drop in PCE (86%) during the measured time period . Comparison of the results showed that the lowest rate of efficiency loss (1%) was obtained for the solar cell with a 1: 1 molar iodine-bromide ratio with an energy conversion efficiency of 9%.

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In this study, CH₃NH₃SnI₃ Perovskite thin films were­ prepared on different substrates, Glass, FTO, and mesoporous TiO₂ by easy and cheap thermal evaporation method in one step. Then, structural, morphology and optical properties of the layers were investigated. The XRD patterns and Raman spectra showed that all samples have α-phase tetragonal Perovskite structures and crystallinity, as well as the morphology of the samples significantly changes as the substrates changes. Investigation of the optical properties of the samples showed that despite small thickness of the layers (about 200 nm), the absorption coefficient of the layers (specially the layer grown on FTO substrate) is significantly large (in order of 10⁵ cm^-1). This result with the values of the bandgap of the layers (1.28-1.53 eV) show that the synthesized CH₃NH₃SnI₃ Perovskite thin films are a very good candidate for using in solar cells as absorber layers.

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In this research, MASnICl₂ and FASnICl₂ thin layers were synthesized by the one-step spin coating method, and then their structural, optical and electrical properties were investigated. The study of these samples (structural properties) showed that the layers have a tetragonal structure (α- phase perovskite), and with the change of organic cation, the crystallinity and morphology of the layers significantly change. These changes also have influences in the optical and electrical properties of the samples. The perovskite layers have a high absorption coefficient (of the order of 10⁵ cm^-1) in the visible range. The bandgap for the FASnICl₂ layer was 1.48 eV and for the MASnICl₂ layer was 1.54 eV. A strong peak close to bandgap was observed in the room temperature PL of the layers, which was remarkably more intense for the FASnICl₂ sample. This study showed that the FASnICl₂ layers have better crystallinity, lower electrical resistance, higher optical sensitivity and acceptable optical response comparing the MASnICl₂ layers, and therefore, they can be suitable options for use as an adsorbent layer in perovskite solar cells.

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In this research, nanocrystals of metal-organic frameworks (MOF), based on metal ions of aluminum, bismuth, cobalt, chromium, copper, tin, titanium and zinc with homogenous morphology were synthesized using a solvo-thermal method as an organic framework to form the porous MOF-doped TiO₂ for electron transport layer in perovskite solar cells. By thermally decomposing the MOF-doped TiO₂ layer in air, the organic template was removed, and porous MOF-doped TiO₂ was obtained.  The results of optical properties of crystal structure of porous MOF-doped TiO₂ layer showed that doping with MOF remarkably improved the absorption ability of TiO₂-MOF layer toward the Uv-Vis region with band gap energy less than of 2.7 eV.  The photoluminescence spectroscopy was conducted to illustrate the improvement of electron transfer in the doped material further. The power conversion efficiency of solar cells using MOF-doped TiO₂ was found to improve in comparing that of solar cells using pristine mp-TiO₂.

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Bismuth-based lead-free perovskites are considered as a promising alternative to lead perovskite, whose toxicity and instability are a major challenge in their commercialization. However, lead-free provskites are strongly restricted by low efficiency due to the high band gap and poor quality of layer formation in perovskite solar cells. In this research, the double perovskites Cs₂AgBiI₆ has been synthesized from solution-based synthesis heating under reflux and then the film was deposited on mp-TiO₂ substrate by thermal evaporation method. The effects of annealing and thickness on the optical and electrical properties of deposited layer were investigated for using as absorber layer in perovskite solar cells. The optimal thermal annealing temperatures (250 °C) would significantly extended the wide absorption range up to 650 nm and reduces appreciable direct band gap of 1.92 eV. The results from analysis of the current density–voltage and photoluminescence spectra, show that the best power conversion efficiency of 0.9% obtained at optimal condition of 250 °C annealing temperature and 400 nm thickness of Cs₂AgBiI₆ film for using in mesostructure lead-free perovskite solar cells. These optimal conditions are clearly consistent with the charge transfer characteristics and stability of the samples.