Surface Of Silicon Solar Cells Research Articles

Simulation of the ductile machining mode of silicon

Diamond wire sawing has been developed to reduce the cutting loss when cutting silicon wafers from ingots. The surface of silicon solar cells must be flawless in order to achieve the highest possible efficiency. However, the surface is damaged during sawing. The extent of the damage depends primarily on the material removal mode. Under certain conditions, the generally brittle material can be machined in ductile mode, whereby considerably fewer cracks occur in the surface than with brittle material removal. In the presented paper, a numerical model is developed in order to support the optimisation of the machining process regarding the transition between ductile and brittle material removal. The simulations are performed with an GPU-accelerated in-house developed code using mesh-free methods which easily handle large deformations while classic methods like FEM would require intensive remeshing. The Johnson-Cook flow stress model is implemented and used to evaluate the applicability of a model for ductile material behaviour in the transition zone between ductile and brittle removal mode. The simulation results are compared with results obtained from single grain scratch experiments using a real, non-idealised grain geometry as present in the diamond wire sawing process.

High symmetry nano-photonic quasi-crystals providing novel light management in silicon solar cells

Reduction of surface reflection loss is crucial for high efficiency next generation Si solar cells. Surface texturing provides a viable method to reduce loss over the full solar bandwidth. Previous studies have concentrated on simple moth-eye silicon pillar arrays protruding from the surface. Using FDTD simulation methods, we undertake a systematic investigation into performance benefits provided by complex semi-random photonic quasi-crystal surface patterning methodologies whereby arrays of air holes are etched deep into the solar cell surface. In contrast to other studies we carefully investigate the effect of lattice symmetry, systematically comparing performance of simple 6-fold symmetric triangular photonic crystal patterning to 12 fold symmetry photonic quasicrystal patterning and infinitely symmetric 2D Fibonacci patterning. We optimize key geometric parameters such as lattice pitch, hole size and etch depth to maximize optical performance for each lattice type. 12 fold photonic quasi crystal lattice is found to provide best overall anti-reflectance performance providing a solar-corrected average reflectance of 8.3% for a hole depth of 1.5 µm and 300 nm diameter, in comparison to 36.4% for a bare silicon solar cell surface. Practical feasibility of the optimal designs is demonstrated by fabrication of physical prototypes consisting of arrays of nm scale air-holes etched into the surface of a silicon slab fabricated Using e-beam lithography and ICP/RIE etching. FDTD Simulation methodology is validated by convergence studies as well as comparison to optical measurements on these fabricated devices. Furthermore, in contrast to previous studies we provide an in depth analysis of the physical mechanisms responsible for reduction in surface reflection, determining the parameter space where conventional Gaussian optical processes such as effective refractive index, refraction and Fresnel reflection dominate, vs parameter space where sub wavelength photonic crystal scattering effects play the main role. We finish up with an analysis of electrical performance for the optimal designs to further validate real world performance. Taking electrical performance into account we determine that infinite-symmetry 2D Fibonacci patterning far outperforms lower symmetry 12 fold and triangular arrangement. We believe that this is the first in depth investigation into 2D Fibonacci patterning in silicon solar cells.

Characteristics and development of interdigital back contact solar cells

Silicon-based solar cells are an important field for the development of the photovoltaic industry. The grid electrode on the front surface of the traditional silicon solar cell causes shading loss. However, the positive and negative electrodes are placed on the back surface of the interdigitated back contact(IBC) solar cell, which causes no shading loss and improvement of photoelectric conversion efficiency. The core of the IBC silicon solar cell is the interface control, field effect control and the design of the positive and negative electrode patterns on the back. Different manufacturing processes ensure the accuracy of the grid electrode and reduce production costs. This paper systematically introduces the structure and interface characteristics and development history of IBC solar cells, and looks forward to the development trend and application prospects of IBC solar cells.

Research on the fabrication and anti-reflection performance of diamond-like carbon films

In this work, a radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) system has been employed to fabricate diamond-like carbon (DLC) films for the application in crystalline silicon solar cells. The morphological, structural and optical properties of the synthesised DLC films were investigated under different deposition times, different plasma discharge powers, different CH4 flow rates, and different substrate temperatures, respectively. It is shown that, when the plasma discharge power was 100 W, the CH4 flow rate was 60 sccm, and the substrate temperature was 100 °C, the synthesised DLC film features a high transmittance of 95%, a low surface reflectivity of approximately 14%, a wide optical band gap of 2.6 eV, as well as a uniform and dense texture. Subsequently, the DLC films with different thicknesses were grown on the surface of crystalline silicon solar cells as anti-reflection coatings. The solar cell current-voltage characteristic testing system was used to investigate the change of solar cell performance parameters, i.e., Jsc, Voc, FF and η. After the growth of a DLC film with a deposition time of 20 min on the surface of a crystalline silicon solar cell, the photovoltaic conversion efficiency of the solar cell increases from 4.12% to 5.2%. This work demonstrates that the DLC film has a promising application potential as an anti-reflection layer in crystalline silicon solar cells.

Surface roughness and crystallinity of silicon solar cells irradiated by ultraviolet femtosecond laser pulses

AbstractNano/microfabrication experiments on the surface of silicon solar cell are performed by ultraviolet femtosecond laser in the fluence range from 0.10 to 0.70 J/cm2. The surface morphology change of sample was observed by a laser scanning microscopy and a scanning electron microscope. The crystallinity of surface irradiated by laser pulses was evaluated by Raman spectroscopy. The ablation threshold for silicon was estimated to be 0.10 J/cm2. We successfully produced nano‐structures on the surface of silicon solar cell maintaining single‐crystalline with the irradiation at the laser fluence of 0.10 J/cm2.

Improvement of light-harvesting efficiency of amorphous silicon solar cell coated with silver nanoparticles anchored via (3-mercaptopropyl) trimethoxysilane

Owing to small size effect and large surface area, silver nanoparticles (Ag NPs) exhibit special physical properties and are widely used in different applications. One of the significant applications is that Ag NPs can be coated on the glass surface of solar cell to increase the light-harvesting efficiency of solar cell due to the plasmonic resonance and scattering effect. In this study, Ag NPs used for the coating of solar cells were synthesized via a chemical reduction method. The effect of the concentration of sodium borohydride (NaBH4) as reducing agent and 1-dodecanethiol (DDT) as capping agent on the size and shape of Ag NPs synthesized have been investigated. The synthesized Ag NPs were characterized using UV–vis spectroscopy, X-ray diffraction, energy-dispersive X-ray spectrometry and ATR-FTIR spectroscopy; while the particle size, morphology and topology of Ag NPs were examined by scanning electron microscopy and atomic force microscopy. By coating the glass surface of amorphous silicon solar cells with a uniform array of Ag NPs with the particle size of > 350 nm, a power conversion efficiency (PCE) enhancement of approximately 41% has been achieved. (3-mercaptopropyl) trimethoxysilane (MPTMS) was used as the adhesion promoter to anchor Ag NPs on the silicon surface of solar cells. With 7% of MPTMS, the array of Ag NPs formed on the glass surface was found being the most evenly distributed with a densely packed surface coverage, which resulted in 46% of PCE enhancement of the silicon solar cells.

Investigation of light trapping mechanism of Silicon solar cell performance utilizing Silvaco TCAD

In this project, an investigation on the effect of difference shapes of the top surface silicon (Si) solar cell as an antireflective (AR) layer was carried out. Texturing the top surface of silicon solar cell helps to reduce light reflection from the solar cell. The different surface texturing which is planar structure, columnar structure and pyramid structure was created and simulated using Athena process simulator by SILVACO TCAD tools. The structures were then loaded into ATLAS device simulator to extract the electrical performance parameters of the solar cell. The results showed that the planar, pyramid and columnar structures of the Si solar cells exhibited efficiency of 2.04%, 2.18% and 2.39% respectively. The short circuit current, Isc, open circuit voltage, Voc and the maximum power, Pmax for the columnar structures are 2.35444 nA, 0.366605 V and 0.630363 nW respectively. The columnar structures exhibited better performances compared to the other structures indicating the columnar structure is good in trapping the light and efficiently collecting the current carrier at the electrode.

Impact of Al Doping on Surface Passivation of TiOx on Si

Titania (TiOx) is re-emerging to be a passivating material for the surfaces of high-efficiency crystalline silicon solar cells. Numerous sources in the literature suggest that the surface passivation and thermal stability of TiOx deteriorates with increasing film thickness when the TiOx film is thicker than a sufficient thickness. To circumvent this limitation, this study presents a novel process of Al-doped TiOx (TiOx:Al) film, which demonstrates the potential for improved thermal stability and surface passivation. Based on grazing incident X-ray diffraction and UV-Raman measurements, the incorporation of Al impurity in TiOx effectively restrains the crystal phase transformation of the amorphous TiOx layer during deposition. Furthermore, the TiOx:Al films provide better thermal robustness up to 350 °C, which makes it highly compatible with Si solar cell fabrication processes.

Reducing light reflection by processing the surface of silicon solar cells

This study discussed a surface processing technique for improving the energy conversion rate of solar cells with silicon as the substrate. The technique involves texturing the surface of a silicon substrate and coating it with an antireflective layer to enhance its antireflective property and thereby its photoelectric conversion efficiency. Double surface texturing (DST) texture was formed through photolithography and anisotropic wet etching, and radio frequency magnetron sputtering was performed to deposit the SiO2/TiO2 double-layer antireflective coating to reinforce the surface texture of a silicon solar cell. Subsequently, a scanning electron microscope was employed to analyze the DST texture before and after the surface was coated with a double-layer antireflective coating (ARC). An UV–VIS spectrophotometer attached with an integrating sphere was then applied to measure the light absorption rate of the processed surface at different wavelengths. After optimum DST and double-layer ARC treatments, the average reflectance within the visible light reduce to 9.94%, which means the absorption of incident light into the absorption layer was enhanced to improve the energy conversion efficiency of silicon solar cells.

Unassisted Water Splitting Using Standard Silicon Solar Cells Stabilized with Copper and Bifunctional NiFe Electrocatalysts.

Silicon photovoltaic cells functionalized with water-splitting electrocatalysts are promising candidates for unassisted water splitting. In these devices, the total surface of silicon solar cells is covered with electrocatalysts, causing issues with (i) stabilizing silicon solar cells in water and (ii) device efficiency due to parasitic optical absorption in electrocatalysts. We describe and validate a water-splitting device concept using a crystalline silicon solar cell where the front side is covered with an insulating Si3N5 antireflection coating. The Ag contacts, fired through the antireflection coating, are removed and subsequently substituted with NiFe layered double hydroxide (LDH) or Cu/NiFe-LDH electrocatalysts. In this device, only the site of Ag contacts, nearly 2% of the total device area, is covered by the electrocatalyst. We found that this small area of the catalyst does not limit device performance and the addition of a Cu interlayer between Si and NiFe-LDH improves device performance and stability. The unassisted water-splitting efficiency of 11.31%, measured without separating the evolved gases, is achieved using a device composed of three series-connected silicon solar cells and an NiFe-LDH/Cu/Ni-foam counter electrode in a highly alkaline electrolyte.

Degradation and Regeneration of n +-Doped Poly-Si Surface Passivation on p-Type and n-Type Cz-Si Under Illumination and Dark Annealing

Degradation and regeneration of recombination parameters can occur in the bulk and at the surfaces of silicon solar cells. This article focuses on the time-resolved analysis of the recombination properties of textured 1.7 Ω cm boron-doped p -type Cz-Si and 5 Ω cm phosphorus-doped n -type Cz-Si wafers, where the surfaces are passivated by n + poly-Si on interfacial oxide layers exposed to a rapid thermal annealing (RTA) step in a conventional firing furnace. We observe a thermally activated instability in the lifetime over the entire examined injection range. Our experiments show that minority carrier injection (e.g., by illumination) is not required. Degradation in the surface passivation quality of the poly-Si on oxide layer—corresponding to an increase of the saturation current density J 0 by up to a factor of five—causes the degradation of the effective lifetime. Interestingly, the surface passivation fully regenerates under prolonged annealing and finally improves even beyond the initial state. Both the extent of the lifetime degradation and the change in J 0 depend on the postprocessing treatment temperature which we varied between 80 and 400 °C. Our results indicate that two different processes are responsible for the degradation and the regeneration. Reference samples which did not receive an RTA treatment show no degradation of the surface passivation quality. The RTA treatment applied therefore triggers the degradation effect. A large improvement of the surface passivation quality under prolonged annealing (e.g., at 400 °C) is observed for all samples examined in this study.

Reflectance and crystallinity of silicon solar cells with LIPSS produced by XeCl excimer laser pulses

Laser-induced periodic surface structures (LIPSS) were formed on silicon solar cell surfaces by using a XeCl excimer laser to irradiate them with nanosecond UV laser pulses in the fluence range 0.2–0.6 J/cm2 near the melting threshold fluence (Fth = 0.5 J/cm2) in air. We measured the reflectance of the silicon solar cells after laser irradiation and evaluated their crystallinity by Raman spectroscopy. We found that reflectance and crystallinity depended on laser fluence and number of pulses. For fluence of 0.5 J/cm2, the produced LIPSS contributed to a reduction of ΔR = 3.3% in reflectance at a wavelength of 500 nm. The crystallinity of the fine structures with reduced reflectance was maintained at laser fluences near the melting threshold.

Photovoltaic efficiency enhancement of polycrystalline silicon solar cells by a highly stable luminescent film

Si-based solar cells have dominated the entire photovoltaic market, but remain suffering from low power conversion efficiency (PCE), partly because of the poor utilization of ultraviolet (UV) light. Europium(III) (Eu3+) complexes with organic ligands are capable of converting UV light into strong visible light, which makes them ideal light converter to increase the efficiency of solar cells. However, the low stability of such complexes seriously hampers their practical applications. In this work, we report a highly stable and luminescent ethylene-vinyl acetate (EVA) copolymer film consisting of a Eu3+ complex as a down-shift material, Eu(ND)4CTAC (ND = 4-hydroxy-2-methyl-1,5-naphthyridine-3-carbonitrile, CTAC = hexadecyl trimethyl ammonium chloride), coating of which onto the surface of large area polycrystalline silicon solar cells (active area: 110 cm2) results in an increase of PCE from 15.06% to 15.57%. Remarkable stability of the luminescent film was also demonstrated under light-soaking test for 500 h, and no obvious luminescence degradation can be observed. The remarkable enhancement of the conversion efficiency by 0.51% absolute on such a large active area, together with the high stability of the luminescent film, demonstrates a prospect for the implementation of the films in photovoltaic industry.

SiN/SiO2 passivation stack of n-type silicon surface

Abstract The SiN/SiO2 stack is widely used to passivate the surface of n-type monocrystalline silicon solar cells. In this work, we have undertaken a study to compare the stack layer obtained with SiO2 grown by both rapid thermal and chemical ways to passivate n-type monocrystalline silicon surface. By varying the plateau time and the plateau temperature of the rapid thermal oxidation, we determined the parameters to grow 10 nm thick oxide. Two-step nitric acid oxidation was used to grow 2 nm thick silicon oxide. Silicon nitride films with three refractive indices were used to produce the SiN/SiO2 stack. Regarding this parameter, the minority carrier lifetime measured by means of QSSPC revealed that the refractive index of 1.9 ensured the best passivation quality of silicon wafer surface. We also found that stacks with nitric acid oxidation showed definitely the best passivation quality. In addition to produce the most efficient passivation, this technique has the lowest thermal budget.

Increased Absorption with Al Nanoparticle at Front Surface of Thin Film Silicon Solar Cell

This article presents an effective structural design arrangement for light trapping in the front surface of a thin film silicon solar cell (TFSC). Front surface light trapping rate is significantly enhanced here by incorporating the Aluminium (Al) nanoparticle arrays into silicon nitride anti-reflection layer. The light trapping capability of these arrays is extensively analyzed via Finite Difference Time Domain (FDTD) method considering the wavelength ranging from 400 to 1100 nm. The outcome indicates that the structural parameters associated with the aluminium nanoparticle arrays like particle radii and separations between adjacent particles, play vital roles in designing the solar cell to achieve better light trapping efficiency. A detailed comparative analysis has justified the effectiveness of this approach while contrasting the results found with commonly used silver nanoparticle arrays at the front surface of the cell. Because of the surface plasmon excitation, lower light reflectance, and significant near field enhancement, aluminium nanoparticle arrays offer broadband light absorption by the cell.

OPTICAL AND ELECTRICAL PROPERTIES OF SILICON SOLAR CELLS BY WET CHEMICAL ETCHING

We present a simple method for the texturing of commercial silicon solar cells in a two-step process by etching in an HF solution containing H2O2. This etching process is facilitated by silver nanoparticles which act as catalytic sites. The etching times for the fabrication of nano-pores on the surface are established. The optical properties of the nano-structures on the surface of silicon solar cell were investigated by spectrometer measurements. The samples presented a total reflection coefficient lower than that of silicon solar cells without the treatment. The global efficiency of the silicon solar cell depends on the chosen preparation conditions for the silver ion concentration, and time of wet etching. The textured surface of solar cells showed an increase in efficiency, with a circuit photocurrent higher than that of a reference silicon solar cell without texturing. The J-V curves of various silicon cells are presented and discussed in correlation with the surface morphology.

Evolutionary design algorithm for optimal light trapping in solar cells

Light scattering at rough interfaces is a standard approach to enhance absorption of light in the absorber layers of solar cells due to light trapping. In this work, an automata optimization algorithm, based on the Constructal Theory, is proposed for the heuristic geometric design to enhance light trapping of silicon solar cell surface textures. Surface textures were investigated computationally for light absorption of a normally incident simulated solar spectrum, under constraints of transverse area of the texture. The photogenerated current density was calculated for textures to estimate light trapping. In the automata optimization, Elemental Constructals, consisting of dielectric material blocks, were assembled on top of the solar cell forming a texture. Three variations of the proposed automata algorithm were tested and their capabilities were determined. The best result for this optimization was a photocurrent J=17.48mA/cm2 for grid periodicity above the wavelength and J=18.31mA/cm2 for grid periodicity in the sub-wavelength range. The evolutionary algorithm was also applied to assemble a periodic-disordered texture from fixed shape gratings to better harness incident light. Different textures with fixed shapes of gratings had been investigated to determine optimal geometric parameters. Optimized triangular, trapezoidal, and rounded-tip textures achieved the best results in this phase and were implemented to assemble the periodic-disordered texture which reached J=19.75mA/cm2 for triangular gratings. Results found with this pristine evolutionary algorithm corroborate its efficiency in finding, practically, geometries that lead to greater light absorption with a minimum amount of dielectric materials.

Enhancement for Potential-Induced Degradation Resistance of Crystalline Silicon Solar Cells via Anti-Reflection Coating by Industrial PECVD Methods

The issue of potential-induced degradation (PID) has gained more concerns due to causing the catastrophic failures in photovoltaic (PV) modules. One of the approaches to diminish PID is to modify the anti-reflection coating (ARC) layer upon the front surface of crystalline silicon solar cells. Here, we focus on the modification of ARC films to realize PID-free step-by-step through three delicate experiments. Firstly, the ARC films deposited by direct plasma enhanced chemical vapor deposition (PECVD) and by indirect PECVD were investigated. The results showed that the efficiency degradation of solar cells by indirect PECVD method is up to −33.82%, which is out of the IEC 62804 standard and is significantly more severe than by the direct PECVD method (−0.82%). Next, the performance of PID-resist for the solar cell via indirect PECVD was improved significantly (PID reduced from −31.82% to −2.79%) by a pre-oxidation step, which not only meets the standard but also has higher throughput than direct PECVD. Lastly, we applied a novel PECVD technology, called the pulsed-plasma (PP) PECVD method, to deal with the PID issue. The results of the HF-etching rate test and FTIR measurement indicated the films deposited by PP PECVD have higher potential against PID in consideration of less oxygen content in this film. That demonstrated the film properties were changed by applied a new control of freedom, i.e., PP method. In addition, the 96 h PID result of the integrated PP method was only −2.07%, which was comparable to that of the integrated traditional CP method. In summary, we proposed three effective or potential approaches to eliminate the PID issue, and all approaches satisfied the IEC 62804 standard of less than 5% power loss in PV modules.

Experimental demonstration of a tapered silicon core–shell nanowire solar cell enhanced by a nickel silicide contact

A wholly passivated silicon core–shell nanowire solar cell incorporating a nickel silicide (NiSi) contact shows reduced series resistance. The configuration’s highly ordered vertical nanowire array is produced by the top-down method on a silicon solar-cell surface. The prepared samples demonstrate reflectance of ∼65 % to 7%. The sample without the NiSi contact has a high short-circuit current density of 31.0 mA / cm2. The cells with ∼5 nm NiSi show an improved fill factor of 70%, contributing to a high power-conversion efficiency of 10.8%.

Reduced Fresnel Reflection by Photon Tunneling in Antireflection Coating Layer of Crystalline Si Solar Cells

We investigated the light absorption of multi-antireflective layers on the microtextured surface of a crystalline silicon solar cell. Triple antireflection coating layers were deposited with SiNx/SiO2/SiNx thin films. A 20 nm SiO2 layer was sandwiched between two SiNx layers, forming a total thickness around 90 nm. Triple antireflection layers showed the enhanced light absorption in the infrared wavelength range, which is consistent with the Si energy band gap region. Further optical simulation on triple antireflection layers using a transfer matrix method showed similar reflection behavior to that of the experimental results. The SiO2 layer sandwiched between the SiNx thin films acts not only as the Fresnel reflection layer in the blue and UV spectral regions, but also as a photon tunneling layer in the infrared spectral region.