International Journal of

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By introducing a thin ZnO layer as an optical spacer, we have demonstrated that inserting this layer between an active layer and a reflective electrode results in a re-distribution of the optical electric field inside bulk heterojunction solar cells. A theoretical analysis by optical modeling showed that the thin ZnO layer could shift the position of the maximum of the electric field into the absorbing layer. Theoretical calculations were compared with experimental results for devices with and without an optical spacer. By using a ZnO optical spacer layer, a significant increase was observed in the short circuit current density of J-V curves. This increase might be due to harvesting more lights and also hole-blocking by the ZnO layer. Both electrical and optical characteristics of the device provided improved results in the power conversion efficiency of the bulk heterojunction solar cell up to 3.49%.

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Planar superstrate CuInS2 (CIS) solar cell devices are fabricated using totally solution-processed deposition methods. A titanium dioxide blocking layer and an In2S3 buffer layer are deposited by the spray pyrolysis method. A CIS2 absorber layer is deposited by the spin coating method using CIS ink prepared by a 1-butylamine solvent-based solution at room temperature. To obtain optimum annealing temperature, these layers are first annealed at 150°C and then annealed at 210°C, 250°C and 350°C respectively. The optimum annealing temperature of the layer is found to be 250°C, where 23 mA current density and 505 mV open circuit voltage are measured for the best fabricated solar cell sample.

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Nanostructures of noble metal materials have been used in organic solar cells for enhancement of performance and light trapping. In this study, we have introduced branched silver cauliflower-like nanopatterns as sub-wavelength structured metal grating in organic solar cells. Self-assembled fabrication process of branched nanopatterns was carried out on a bio-template of cicada wing nanonipple arrays using a gas aggregation dc magnetron sputtering nanocluster source without size filtration. The branched nanostructures provide surface gaps with dimensions near the organic exciton diffusion length, which prevents recombination of charge carriers. An increased power conversion efficiency of 14.8% compared to that of the planar device was achieved mainly due to the enhancement in the short-circuit current density. Besides, these branched cauliflower-like nanopatterns had enhanced optical light absorption in the solar cell as a result of enhancing the optical path length of the reflected light in the active layer and plasmonic effects of the noble metal material.

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In this paper a novel anti-reflection (AR) coating based on silicon nano-bars is designed and its impact on the performance of crystalline silicon (c-Si) thin-film solar cells is extensively studied. Silicon nano-bars with optimized size and period are embedded on top of the active layer, under a 100nm Si₃N₄ layer. As a result of the proposed layer stack, an inhomogeneous intermediate layer with effective refractive index amid the two layers is formed and a graded refractive index AR coating is achieved, which has a substantial effect on broad, omnidirectional reduction of the reflection spectra. To validate our claim, the proposed structure as well as four conventional AR coatings are simulated and through the numerical analysis of both the spectral response of the reflection factor and the silicon active layer absorption spectra, it is shown that the proposed design outperforms conventional already existing AR coatings, and in addition provides a strong coupling of the incident light to the active layer, while improving the overall efficiency of the thin-film solar cell.

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In this article, the effect of plasmonics properties of metal nanorods and nanoparticles on solar cell performance were investigated and simulated. Due to the classic solar cell disadvantages, it seems that a plasmonic solar cell is one of these methods. In plasmonic solar cells, because of plasmonic effect, a high electric field builds around metal nanoparticles so that high conversion efficiency is available. In this study, it is shown that the near-field electromagnetic wave severely affects the generation rate, which handles the carrier’s generation in the solar cell equations. By manipulating the plasmonic properties of nanoparticles or nanorods in solar cells structure, distribution of the electromagnetic fields are altered. In this work, optical power and generation rate related to the poynting vector is calculated. So, for improving the generation rate as an important parameter in solar cells, the alteration of nanoparticles or nanorods material, shape, inter-distance between them and medium material, are done. Finally, the comparison between classical solar cell and our improved structure is performed.

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In this paper, tetragonal chalcopyrite (CIGS) Cu(In_xGa_1-x)Se₂ with x=0, 0.5, 0.8, 1 are synthesized by heating-up method. These nanoparticle structures differ in morphology and absorption properties due to the synthesis temperatures of 250, 255, 260, 265, 270 and 280 ºC, and gallium molar ratio over the total gallium and indium contents. These features are studied using scanning electron microscope, X-ray diffraction and absorption spectroscopy in visible, ultra-violet and near-infrared wavelengths. Results indicate that by increasing gallium content, absorption edge rises toward the visible light. Any modification in the absorption edge changes the band gap and as a result the energy gap and the absorption of cell increases considerably. Also in the heating-up method, increasing the reaction temperature improves nanoparticles crystallites. This leads the absorption improvement and higher cells efficiency. Produced nanoparticles are spherical shape with are varying the diameter around 30-80 nm.

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To investigate the plasmonic effect in perovskite solar cells, the effect of depositing Au@SiO₂ nanoparticles on the top and the bottom of mesoporous TiO₂ layers was studied. First, Au@SiO₂ nanoparticles were synthesized. The particles were then deposited at the different interfaces of mesoporous TiO₂ layers. Although the two structures show approximately similar optical absorption, only cells with Au@SiO₂ nanoparticles deposited at the bottom of the mesoporous TiO₂ layers demonstrated an improved photocurrent performance compared to the reference cells. This structure shows a short-circuit current density (JSC) of 20.7 mA/cm² and open circuit voltage of 1081 mV. This enhancement may be attributed either to the interface surface engineering or plasmonic resonance of Au@SiO₂ nanoparticles depends to the NPs size and position.  

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In this article, the effect of plasmonic properties of metal nanoparticles with different shapes, and moreover, their plasmonic-photonic interaction, on solar cell performance were investigated and simulated. Because of low conversion efficiency and then high cost of solar cells, it is difficult to commercialize and replace them with conventional energy resources. But in recent years, the plasmonic solar cell has been very popular. In this study, it is shown that the enhancement of near-field electromagnetic waves severely affects the generation rate, which handles the carrier’s generation in the solar cell equations and causes alteration of the photocurrent. This means that by manipulating the plasmonic properties of nanoparticles (shape and density) and their interaction with photons in solar cell structure, distribution of electromagnetic fields will be altered. Hence, the optical power related to the poynting vector is changed. So, with the aim of improving the solar cell some important parameters such as alteration of nanoparticle shape and their inter-distance were investigated. Finally, a comparison between traditional solar cells and our improved structure was undertaken.

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Recently, organo–metal halide perovskites have attracted much attention of the scientific community relating to their successful application in the absorber layer of low-cost solar cells. However, enough is known about the material and device properties, to realize that much remains to be learned.
In this paper, the electrical and optical properties of perovskite solar cells are investigated using the COMSOL Multiphysics simulation program. It is a study of the influences of carrier diffusion length (L), dielectric constant (ε_r), the valence band offset (VBO) of absorber/hole transport materials (HTM) and illumination intensity on fill factor (FF), short-circuit current density(J_SC), performance (PCE), and open-circuit voltage(V_OC). Also, J-V characteristics are calculated for different ε_r values. The simulation results point to the great dependence of efficiency on the carrier diffusion length of absorber layers. It is shown that, to obtain a high rate of efficiency, the relative permittivity should not be higher than 45.
 

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Owing amongst other to its high electron mobility, fullerene C70, has been widely used as an electron transporting layer in organic solar cells. In this research, we report the use of C70 thin films as electron transport layers of planar perovskite solar cells (PSCs) using a conventional device structure. The thickness of the C70 layer has been optimized to achieve the best efficiency of 12%. It is demonstrated that ultra-thin C70 films can effectively block holes and thus become selective to the transport of electrons in PSC devices.
 

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In this paper, a thin film silicon solar cell with anti-reflection coatings on front surface and the combination of periodic grating and photonic crystal on its back surface has been considered. The thickness and number of anti-reflection coatings, as well as the geometric and physical parameters of photonic crystal and grating are optimized to increase the optical absorption of solar cell. The simulations have been performed using the finite difference time domain method with Lumercial software. The results show that the optical absorption of solar cell has been increased significantly by utilizing the anti-reflection coatings, photonic crystal and grating.

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In this work, the effect of changing the dimensions of the layer structure on the collection of electrical charge carriers which been produced in the thin film composed of P3HT[1] and PCBM[2] that is between two electrodes, using the Monte Carlo numerical simulation with Bortez, Callus and Lebowitz algorithms, with checkered structure and different dimensions 60×15×5 sites, 60×30×5 sites, have been the conditions of the layers. At first, the average number of electrons and holes produced on the cathode and anode electrodes in two stages (simultaneous injection of excitons, without and with the presence of deep traps) was calculated and it was concluded that, by increasing layer width, the average number of electrical charge carriers collected on the electrodes has decreased, which has a direct impact on production of layer circuits and solar cell performance. Finally, the amount of external quantum efficiency of the layers was also calculated. In 60×15×5 sites layer, in two stages – without and with the presence of traps – the average value of external quantum efficiency 52.3% and 42.43% was obtained and in 60×30×5 sites layer, the value of 42.43% and 37.9% was calculated.

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One of the main challenges for perovskite solar cell (PSCs) structures is their high sensitivity to humidity and ambient temperature, which significantly lowers the lifespan of these devices. Low stability of this devices is considered one of the principal limitations to make them commercialized. To increase the stability of the solar cell is to encapsulate the solar cell. The encapsulation is to cover the device with a non-reactive material, which prevents the penetration of ambient moisture and increases the thermal stability of the cell. If the uncoated device is exposed to continuous incident light for several hours, its structure is damaged while encapsulated device has a longer duration time. Several methods have been proposed for encapsulating a perovskite solar cell. The principal strategy of these methods involves deposition of a thin layer of polycarbonate polymer on the perovskite solar cell structure, resulting in layers of the desired structure. After fabrication and encapsulation process, the order of the various layers are FTO / bl-TiO₂ / mp-TiO₂ / Perovskite (CH3NH3PbI₃) / Spiro-OMETAD / Au / Polycarbonate Polymer. To increase the effective stability, the glass coating is placed on the polycarbonate polymer. After acquiring sufficient adhesion between the glass coating and the polymer layer on the structure of PSCs, UV epoxy is used to seal the whole structure. Having performed the encapsulation, the samples were exposed every day to 85% constant humidity and 85°C temperature for 10 hours and it was observed that the cell efficiency, under the mentioned conditions and after successive measurements, maintained to a high extent.