Papers by Keyword: Solar Cell

Abstract: Silicon chip has been widely used in solar cell recently. The thinning of silicon chip, easily inducing surface defects, becomes necessary to produce solar cells more efficiently. The surface defects resulting in stress concentration on the silicon chip surface would be the source of chip failure. In this study, the finite element analysis was used to investigate the stress distribution near the surface crack of a solar cell on which the nanostructures were introduced to alleviate the induced stress. For the solar cell model, positive silver and negative aluminum electrodes were added on the top and bottom sides of silicon chip. The solar cell under four-point bending was simulated in analysis with and without nanostructures. The results show that the stresses reduce more than 50 % for the solar cell model with nanostructures. When the crack depth is deeper enough, the stress at crack tip is higher than that at junction near the electrode and the crack leads to the failure of solar cell. The effect of different section length of nanostructures on the stress distribution caused by the surface crack was also discussed.

Abstract: The research is aimed to the investigation of the microstructure defects in the silicon and the thin-film CIGS solar cells. These defects have their origin mainly in the technological process of a production but they can be caused by an accidental mechanical stress during a normal operation, too. That leads to a formation of the micro-cracks and the fractures, which have a significant effect on a device efficiency and reliability. The reverse-bias conditions are usually used for the defects charac- terization purposes. The mechanical induced defects increase a reverse current which leads to a strong overheating in the local breakdowns and the surroundings areas, thus for the defects localization pur- poses an infrared imaging and an electroluminescence method is used. Beyond these commonly used methods the results from the electrical current noise fluctuations observed in a frequency domain are presented in this work. The noise fluctuations measurement is a reliable indicator of a device quality and allow us to qualify the device damage extent. Using combination of these methods it is possible to localize the particular defects, assess the degree of a damage and classify the elimination process of the particular defects.

Abstract: Key steps in the fabrication of high-efficiency a-Si:H/c-Si heterojunction solar cells are the controlled pyramid texturing of the c-Si substrates to minimize reflection losses and the subsequent passivation by deposition of a high-quality a-Si:H layer to reduce recombination losses. This contribution reviews our recent results on the optimization of the wet-chemical texturing of crystalline Si wafers for the preparation of heterojunction solar cells with respect to low reflection losses, low recombination losses and long minority carrier lifetimes. It is demonstrated, that by joint optimization of both saw damage etch and texture etch the optical and electronic properties of the resulting pyramid morphology can be controlled. Effective surface passivation and thus long minority charge carrier lifetimes are achieved by deposition of intrinsic amorphous Si ((i) a-Si:H) layers. It is shown, that optimized (i) a-Si:H deposition parameters for planar Si (111) wafers can be transferred to a-Si:H layer deposition on random pyramid textured Si (100) wafers. Statistical analysis of the pyramid size distribution revealed that a low fraction of small pyramids leads to longer minority charge carrier lifetimes and, thus, a higher V_oc potential for solar cells.

Abstract: The performance of copper indium gallium disulfoselenide (CIGSSe) solar cells strongly depends on the band bap of absorbing layer of CIGSSe. The device performance can be improved by fabricating multi band gap layer of CIGSSe. However, the fabrication of multi band gap CIGSSe using non-vacuum techniques is challenging. In this study, we fabricated solar cell devices which consisted of multi band gap Cu (In,Ga)(S,Se)₂ thin films. The CIGS thin films were prepared by the spray-pyrolysis of aqueous precursor solutions of gallium (gallium chloride; GaCl₃), copper (indium chloride; CuCl₂), indium (indium chloride; InCl₃), and Sulphur (thiourea; (SC(NH₂)₂) sources on Mo-coated glass substrate. The as-sprayed thin films were then selenized at 500 °C for 10 minutes.After selenization, CIGS films were transformed to Cu (In,Ga)(S,Se)₂ (CIGSSe). The CIGS films with different composition were deposited again on top of selenized CIGSSe films and selenization process was repeated, hence multi band gap CIGSSe films were fabricated. The Chemical bath deposition (CBD) process was used to deposit cadmium sulphide (CdS) buffer layer. The solar cell fabricated with the device configuration of glass/Mo/CIGSSe/CdS/i-ZnO/AZO showed a power conversion efficiency of 6.51%.

Abstract: In this paper, we present two optical microconcentrator systems consisting of an array of microlenses formed with an intermediate layer deposited between a textured glass plate and the front surface of a silicon solar cell and polydimethylsiloxane (PDMS) microlenses based on replication of molds etched on glass. The optical coupling microlenses are fabricated using simple photolithography techniques that make the design compatible with silicon technology and large-scale manufacturing.We experimented with a honeycomb texturization on Corning glass plate having an area of 2x2 cm². A wet etching process that led to a transparent surface with micro-cavities of 20 μm diameter and a depth of 6 μm was used. The intermediate layer was chosen depending on the refractive index. Materials with the refractive index in the range of 1 - 1.43 were experimented. The structures of silicon solar cells covered with the intermediate layer and texturized glass were characterized by illuminating and measuring the short-circuit photocurrent. It was obtained an improvement of 6.7 % of the short-circuit photocurrent for the optical microconcentrator system solar cells as compared to a structure covered with an untextured glass plate without intermediate layer. The microconcentrator consisting of the PDMS microlenses gave better results, an increase of the photocurrent of over 9%.The simulations of this system were done by using an OptiFTDT software. The aim of the simulations was to establish the distribution of the radiation which crosses the optical microconcentrator system and hits the solar cells surface. The simulation results are in agreement with the obtained experimental data.

Abstract: There is a strong and growing worldwide research on exploring renewable energy resources. Solar energy is the most abundant, inexhaustible and clean energy source, but there are profound material challenges to capture, convert and store solar energy. In this work, we explore 3C-SiC as an attractive material towards solar-driven energy conversion applications: (i) Boron doped 3C-SiC as candidate for an intermediate band photovoltaic material, and (ii) 3C-SiC as a photoelectrode for solar-driven water splitting. Absorption spectrum of boron doped 3C-SiC shows a deep energy level at ~0.7 eV above the valence band edge. This indicates that boron doped 3C-SiC may be a good candidate as an intermediate band photovoltaic material, and that bulk like 3C-SiC can have sufficient quality to be a promising electrode for photoelectrochemical water splitting.

Abstract: Sublimation-grown 3C-SiC crystals were implanted with 2 atomic percent of boron ions at elevated temperature (400 °C) using multiple energies (100 to 575 keV) with a total dose of 8.5×10¹⁶ atoms/cm². The samples were then annealed at 1400, 1500 and 1600 °C for 1h at each temperature. The buried boron box-like concentration profile can reach ~2×10²¹ cm^-3 in the plateau region. The optical activity of the incorporated boron atoms was deduced from the evolution in absorption and emission spectra, indicating possible pathway for achieving an intermediate band behavior in boron doped 3C-SiC at sufficiently high dopant concentrations.

Abstract: The silver pastes containing Ag₂O powder, Ag powder, α-terpineol, ethyl-cellulose and Pb-free glass were synthesized for crystalline silicon (c-Si) solar cells. It was found that α-terpineol assisted the decomposition of Ag₂O powder and effectively lowered the decomposition temperature of Ag₂O. Ag nanoparticles were produced during the decomposition of Ag₂O, which helped to reduce the sintering temperature of the silver pastes. The Ag₂O-aided silver pastes were fired on polycrystalline silicon solar cells at various temperatures, and large plate-shaped Ag crystallites appeared at the interfaces between the sintered pastes and the emitter, which ensured a good electrical contact. The contact resistivity of Ag₂O-aided silver paste with an optimal ratio of Ag₂O to Ag was lower than that of the paste with pure Ag powder. The lowest contact resistivity of Ag₂O-aided Pb-free silver pastes sintered at 800°C was 0.029 Ω⋅cm², which was close to that of commercial silver paste that contained Pb-based glass (0.026 Ω⋅cm²). The experimental data demonstrated that the addition of Ag₂O reduced the contact resistance and promoted the sintering of Pb-free silver pastes, and Ag₂O-aided Pb-free silver paste could be a promising candidate used for front-contact electrode of c-Si solar cells.

Abstract: Pyrite (FeS₂) is an important semiconductor material which shows various excellent optical and electrical properties and extensive applied prospect as a new-type, photoelectrical functional materials. In this study, a low cost and efficient simple hydrothermal two-step synthetic method was given to obtain FeS₂ microspheres with 2-3 μm in diameter. The obtained products were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet and visible spectrophotometer (UV-Vis). XRD showed that the synthetic sample consisted of two crystal structures of FeS₂, pyrite and marcasite. SEM observation indicated that FeS₂ microspheres were well crystallized and had good uniformity. UV-Vis spectrum had a strong optical absorption in the region of 200-400 nm wave length. The reaction temperature had an impact on the size of FeS₂ microspheres. A possible mechanism for the size of the FeS₂ microspheres generated at high temperature is smaller than that at low temperature is discussed.

Abstract: This article presents the results of research output voltage characteristics of solar cells on an organic basis with the use of P3HT: PCBM system. There were produced organic solar cells in a coating in air, current-voltage characteristics were measured. It was determined the characteristic influence of a substrate cleaning and annealing temperature of layers applied on fill factor and conversion efficiency.