Silicon Wafer Solar Cells Research Articles

Cost-effective fabrication of a high-conductivity copper electrode for heterojunction solar cells via laser-induced selective metallization.

Replacing expensive silver with inexpensive copper for the metallization of silicon wafer solar cells can lead to significant reductions in material costs associated with cell production, but the susceptibility of the Cu material to oxidation remains a challenging issue to solve. In this study, we investigate copper metallization of Indium Tin Oxide surfaces to define copper grid electrodes for heterojunction cells. We propose a novel laser-induced selective metallization (LISM) method to fabricate large-scale copper electrodes for heterojunction solar cells at low cost. This study includes a comprehensive evaluation of the morphological characteristics and electrical properties of the electrodes. The effects of laser parameters on the morphology, composition, size, and conductivity of copper electrodes are investigated. The goal of establishing the process window is to obtain the optimal laser parameters for manufacturing highly conductive copper electrodes. These optimized parameters will then be employed to fabricate high-performance electrodes for solar cells. Furthermore, a detailed analysis of the mechanism underlying laser selective metallization is provided. The resulting Cu electrodes exhibit high conductivity and low resistivity of 1.98 × 10-5Ω.cm, demonstrating the potential of this method for efficient and cost-effective solar electrode production.

Texturization of Silicon Wafers for Solar Cells by Anisotropic Etching with Sodium Silicate Solutions

The efficiency of silicon solar cells greatly depends on the texturization of silicon wafers used in their fabrication. Texturization reduces the reflectance of the silicon surface which improves the light trapping ability of the solar cells. In this study, aqueous Na2SiO3 solutions were used as etchants in the texturization of monocrystalline silicon wafers. The main objective was to evaluate the performance of the etchant based on the silicon surface reflectance. The surface morphology and etching rate were also investigated. Results showed that Na2SiO3 solutions reduced the surface reflectance of the wafers better than other alkaline etchants. This was brought about by the formation of uniformly distributed pyramidal structures on the surface of the wafer after texturization. The effects of process parameters such as Na2SiO3 concentration, solution temperature and etching time on the reflectance were evaluated and optimized by applying ANOVA and Response Surface Method (RSM). The optimum process condition was found to be 6.2 wt% Na2SiO3, 80°C and 5 min at which the reflectance of the silicon wafer was reduced to 9.27%. Furthermore, the addition of small amounts of IPA (up to 0.03 wt%) to the Na2SiO3 solution reduced the reflectance of the wafer (9.13%) and slightly improved its wettability

Epitaxially Grown p‐type Silicon Wafers Ready for Cell Efficiencies Exceeding 25%

Combining the advantages of a high‐efficiency solar cell concept and a low carbon footprint base material is a promising approach for highly efficient, sustainable, and cost‐effective solar cells. In this work, we investigate the suitability of epitaxially grown p‐type silicon wafers for solar cells with tunnel oxide passivating contact rear emitter. As a first proof of principle, an efficiency limiting bulk recombination analysis of epitaxially grown p‐type silicon wafers deposited on high quality substrates (EpiRef) unveils promising cell efficiency potentials exceeding 25% for three different base resistivities of 3, 14, and 100 Ω cm. To understand the remaining limitations in detail, concentrations of metastable defects Fei, CrB and BO are assessed by lifetime‐calibrated photoluminescence imaging and their impact on the overall recombination is evaluated. The EpiRef wafers’ efficiency potential is tracked along the solar cell fabrication process to quantify the impact of high temperature treatments on the material quality. We observe large areas with few structural defects on the wafer featuring lifetimes exceeding 10 ms and an efficiency potential of 25.8% even after exposing the wafer to a thermal oxidation at 1050 °C.

Etching methods for texturing industrial multi-crystalline silicon wafers: A comprehensive review

Surface texturing for suppressing the reflection losses is the first and foremost step in the solar cell fabrication process. Over the years, multi-crystalline silicon (mc-Si) wafer solar cells dominated the PV market due to their cost-effectiveness. This article reviews various etching methods reported for texturing mc-Si wafers under the light of basic reaction mechanism, general composition of chemicals used, merits, drawbacks, and the progress made towards their commercialization. The article starts with introducing the alkaline etching process used in initial days of mc-Si solar cell production along with its process limitations. Subsequently, evolution of acid texturing process to address the challenges associated with alkaline etching and its journey as an established industrial process are discussed. Thereafter, progressive but expensive texturing methods such as reactive ion etching, laser etching, mechanical grooving and colloidal lithography are also reviewed. Later, the challenges imposed by introduction of diamond wire sawn (DWS) mc-Si wafers on established acid texturing process are presented. Further, remarkable approaches reported towards the effective texturing of DWS mc-Si wafers are discussed. Finally, a summary of reaction chemistry, recent process advances and future roadmap of proposed next-generation texturing scheme known as metal assisted chemical etching is being compiled and presented.

Advanced selection materials in solar cell efficiency and their properties - A comprehensive review

Solar cell layers technology has achieved global standing in the solar cell layers deposition process, and it covers the innovative methods and techniques in significant applications. Recent solar cell layers technology has an advanced interest in a refined approach to enhance performance and highlights the importance of recent proficient procedures for manufacturing. For example, the application is used to search for novel materials for solar cells' layers to clarify the current energy crisis. The technological process and various types of solar cells depend on climate change. Among them, layers of solar cells and silicon wafer solar cells are very encouraging. Solar cell layers technology has led to solar cells being a more reasonable active option in design and production. The productivities facilitated by new solar cells still need to be enhanced for the various processes involved in the additional enhancement from Copper Indium Gallium Selenide (CIGS) microfilms to solar cell crystal structure dye-sensitized solar cells. The hydrophobic coating works as an anti-dust coating, enhancing efficiency and decreasing the cost of cleaning solar cells. In Saudi Arabia Majmaah City, most solar projects are in dry regions, where the dusty weather reduces solar cell efficiency. Therefore, combining these two properties and applying an anti-reflective and superhydrophobic coating will increase solar cell efficiency by 20%. Solar cells' crystal structure results are substituted with layers or new materials to balance environmental impact and toxic nature.

Experimental and Theoretical Study of Oxygen Precipitation and the Resulting Limitation of Silicon Solar Cell Wafers

Commercial silicon is prone to form silicon oxide precipitates during high-temperature treatments typical for solar cell production. Oxide precipitates can cause severe efficiency degradation in solar cells. We have developed a model describing the nucleation and growth of oxide precipitates that considers silicon self-interstitial defects and surface effects influencing the precipitate growth in ∼150 μm thick wafers during the solar cell processing. This kinetic model is calibrated with experiments that cause a well-defined and strong precipitate growth to give a prediction of the carrier lifetime limitation because of the oxide precipitates. We test the oxide precipitate model with scanning Fourier-transform infrared spectroscopy, selective etching, and lifetime measurements on typical Cz solar cell wafers before and after solar cell processes. Despite the relatively rough saw damaged etched surfaces and the thin wafers, we observe recurring ring patterns in the measurements of interstitial oxygen reductions, oxide precipitate etch pit density, and recombination activity by photoluminescence imaging. The concentration of precipitated oxygen correlates with the recombination activity and with the initial interstitial oxygen concentration. However, we found lifetime measurements to be a more sensitive technique to study oxide precipitates and using these we find smaller precipitates not detected by selective etching are very recombination active too. The measured concentrations of precipitated oxygen and lifetime agree fairly well with the predictions of the model.

Stencil-masked phosphorus-implanted silicon for solar cell applications

Stencil-masked phosphorus implantation on silicon wafers is demonstrated for solar cell applications. Line-shaped window patterns with areas of 156 mm × 156 mm and 125 mm × 125 mm are laid out in the silicon stencil mask with diameters of 200 and 300 mm, respectively. According to laser optical microscopy and scanning electron microscopy observation, the phosphorus-implanted line is 100 μm wide with an edge roughness of a few micrometers. Based on the silicon-stencil-masked phosphorus implantation, the fabrication process of alternative phosphorus-implanted and boron-diffused patterns on silicon wafers is proposed. During the post-implantation wet oxidation process, a thick oxide layer is grown on the phosphorus-implanted silicon, acting as a protective layer for the subsequent diffusion of boron. Scanning capacitance microscopy observation reveals the p-type polarity in boron-diffused silicon and the n-type in phosphorus-implanted silicon with homogeneous contrast along the textured surface. Silicon-stencil-masked ion implantation has potential as a selective doping method on silicon wafers for solar cells.

Investigation of Field‐Effect Passivation Created by Hydrogen Plasma Etching of Radio Corporation of America Formed Chemical Oxides on Crystalline Silicon Wafers

This work investigates the interface properties of intrinsic hydrogenated amorphous silicon film passivated wafers that underwent hydrogen plasma cleaning. A high level of interface band bending of nearly −0.6 eV, which corresponds to a fixed charge of −2.2 × 1012 cm−2, is found to be responsible for an effective minority carrier lifetime of over 6 ms on the 4.5 Ω cm n‐type wafer, while such field‐effect passivation is missing in hydrofluoric acid (HF) cleaned wafers. Further study indicates a positive correlation between the extent of surface band bending and doping concentration, together with an inverted U‐shape with respect to the increased annealing condition. The fixed charge on p‐type wafer is found to have a higher “formation energy” compared with the n‐type case, which renders its field‐effect passivation much less effective due to H effusion at high annealing temperatures. With reference to the theory on donor/acceptor‐H complex upon H plasma treatment, the origin and observed properties of the surface band bending on both dopant types are discussed. The unique presence of field effect on hydrogen plasma cleaned n‐type wafers can provide new insights into passivation material selection and structural design of heterojunction silicon wafer solar cells.

PERC silicon PV infrared to ultraviolet optical model

Optical modeling of aluminum back surface field (Al-BSF) and passivated emitter and rear contact (PERC) silicon wafer solar cells are extended into the infrared wavelength range (300–2500 nm). The model incorporates ray tracing to account for pyramidal texture of the front silicon surface, free carrier absorption in the front emitter; bulk silicon wafer, BSF; and Lambertian scattering at the silicon back contact. Total reflectance of pyramidal textured cells with different contact geometries with and without encapsulation are simulated. Simulated reflectance and short circuit current density match well with experimental values. These physics-based optical models serve as input for evaluating optical and thermal management strategies for silicon wafer solar cells.

Texturization of diamond wire sawn multi-crystalline silicon wafers by micro-droplet etching

Diamond wire sawn multicrystalline silicon (DWS mc-Si) solar cell wafers have been known to be difficult to texturize by conventional acidic wet etching texturization process. A novel texturization method based on localized micro-droplet etching (MDE) has been developed, in which the micro-droplet is generated by controlled condensation of thermal vapor from a HF–HNO3–H2O bath. Uniformly distributed micron scale etch-pit type surface textures on DWS mc-Si wafers are made by the MDE process. Their light reflectivity is reduced to 18–21%, and their sawmarks are removed. Full size DWS mc-Si wafer samples were MDE textured, and send to a solar cell fabrication line along with the conventionally wet textured DWS mc-Si wafers as reference, without any adjustment of processing parameters for the MDE textured wafers. The average short circuit current of the MDE textured cells has been found to increase as compared to the reference cells, in a relative ratio approximately matching the final light reflection reduction ratio induced by the MDE textures. The average open circuit voltage and fill factor of the MDE textured cells are found to increase slightly, indicating that the MDE texture has not induced any significant increase in surface recombination of carriers, neither poorer contact of printed grid contact on cell surfaces. In average, 0.52% absolute increase of energy conversion efficiency is obtained.

Silicon solar cell–integrated stress and temperature sensors for photovoltaic modules

AbstractWe propose silicon solar cell–integrated stress and temperature sensors as a new approach for the stress and temperature measurement in photovoltaic (PV) modules. The solar cell–integrated sensors enable a direct and continuous in situ measurement of mechanical stress and temperature of solar cells within PV modules. In this work, we present a proof of concept for stress and temperature sensors on a silicon solar cell wafer. Both sensors were tested in a conventional PV module setup. For the stress sensor, a sensitivity of (−47.41 ± 0.14)%/GPa has been reached, and for the temperature sensor, a sensitivity of (3.557 ± 0.008) × 10−3 K−1 has been reached. These sensors can already be used in research for increased measurement accuracy of the temperature and the mechanical stress in PV modules because of the implementation at the precise location of the solar cells within a laminate stack, for process evaluation, in‐situ measurements in reliability tests, and the correlation with real exposure to climates.

Multidimensional Fourier-Series Solution of the Quasi-Neutral Drift–Diffusion Equations

The semiconductor drift-diffusion equations describe the flow of electrons and holes in solar cells. When fully coupled using Poisson's equation, these equations are strongly nonlinear. However, with the exception of the first micrometer near each surface, the uniformly doped bulk in a solar cell is quasi-neutral, meaning that there is a nearly equal density of excess electrons and holes at each location. The drift-diffusion equations can then be reduced to two differential equations, one approximately linear in the excess carrier density and the other approximately linear in the excess electrostatic potential. The small deviations from linearity can be accommodated by initially treating the nonlinear terms as constant, updating the constants based on the solution result, and then iterating this cycle until convergence is achieved. When these linear differential equations are subject to reflective edge boundary conditions as typically occur when modeling solar cells, they can be solved efficiently using Fourier-series techniques. A specific numerical approach is described in detail and validated for the 2- and 3-D simulations of silicon-wafer solar cells with varying back contact parameters.

A fracture mechanics approach to enhance product and process sustainability in diamond wire sawing of silicon wafers for solar cells through improved wire design

By decreasing the subsurface damage in silicon wafers produced by diamond wire sawing, the mechanical strength of wafers can be increased, and the amount of silicon to be etched in subsequent manufacturing steps can be minimised, enhancing both product and process sustainability. Apart from the sawing process parameters, the subsurface damage in as-sawn silicon wafers is influenced by the design of the diamond wire. We present a fracture mechanics approach for the design of fixed abrasive diamond wires used in wire sawing of silicon wafers for solar cells. Starting from an allowable damage (crack) depth, indentation fracture mechanics and contact analysis are used to determine the wire design parameters, namely the grit protrusion and peripheral distribution of diamond abrasives. The improved wire design can reduce subsurface damage and thereby improve the surface integrity (product sustainability), and reduce the processing time and chemicals used in the subsequent saw-damage removal step (process sustainability).

A fracture mechanics approach to enhance product and process sustainability in diamond wire sawing of silicon wafers for solar cells through improved wire design

A fracture mechanics approach to enhance product and process sustainability in diamond wire sawing of silicon wafers for solar cells through improved wire design

Проблемы при использовании травителя KOH-IPA для текстурирования кремниевых пластин

The wet chemical treatment of monocrystalline silicon wafers, said method comprising texturing, represents one of the fundamental steps of manufacturing techniques of high-efficiency solar cells. As part of this work, methods for texturing single-crystal silicon wafers for solar cells were studied.As a result of studies, the optimal parameters of texturing technology for the studied samples were determined. The main type of etchant for texturing processes, which is a solution of KOH with isopropanol, is also determined.

Photogenerated Carrier Transport Properties in Silicon Photovoltaics

Electrical transport parameters for active layers in silicon (Si) wafer solar cells are determined from free carrier optical absorption using non-contacting optical Hall effect measurements. Majority carrier transport parameters [carrier concentration (N), mobility (μ), and conductivity effective mass (m*)] are determined for both the n-type emitter and p-type bulk wafer Si of an industrially produced aluminum back surface field (Al-BSF) photovoltaic device. From measurements under 0 and ±1.48 T external magnetic fields and nominally “dark” conditions, the following respective [n, p]-type Si parameters are obtained: N = [(3.6 ± 0.1) × 1018 cm−3, (7.6 ± 0.1) × 1015 cm−3]; μ = [166 ± 6 cm2/Vs, 532 ± 12 cm2/Vs]; and m* = [(0.28 ± 0.03) × me, (0.36 ± 0.02) × me]. All values are within expectations for this device design. Contributions from photogenerated carriers in both regions of the p-n junction are obtained from measurements of the solar cell under “light” 1 sun illumination (AM1.5 solar irradiance spectrum). From analysis of combined dark and light optical Hall effect measurements, photogenerated minority carrier transport parameters [minority carrier concentration (Δp or Δn) and minority carrier mobility (μh or μe)] under 1 sun illumination for both n- and p-type Si components of the solar cell are determined. Photogenerated minority carrier concentrations are [(7.8 ± 0.2) × 1016 cm−3, (2.2 ± 0.2) × 1014 cm−3], and minority carrier mobilities are [331 ± 191 cm2/Vs, 766 ± 331 cm2/Vs], for the [n, p]-type Si, respectively, values that are within expectations from literature. Using the dark majority carrier concentration and the effective equilibrium minority carrier concentration under 1 sun illumination, minority carrier effective lifetime and diffusion length are calculated in the n-type emitter and p-type wafer Si with the results also being consistent with literature. Solar cell device performance parameters including photovoltaic device efficiency, open circuit voltage, fill factor, and short circuit current density are also calculated from these transport parameters obtained via optical Hall effect using the diode equation and PC1D solar cell simulations. The calculated device performance parameters are found to be consistent with direct current-voltage measurement demonstrating the validity of this technique for electrical transport property measurements of the semiconducting layers in complete Si solar cells. To the best of our knowledge, this is the first method that enables determination of both minority and majority carrier transport parameters in both active layers of the p-n junction in a complete solar cell.

Surface Roughening of Silicon Wafer Solar Cell by Using ECDM Method

This research proposes surface roughening of silicon wafer solar cell by electrochemical discharge machining (ECDM). The stainless steel was used as negative electrode. The graphite was used as the positive electrode acting as the auxiliary electrode. The potassium hydroxide was used as the electrolyte. The processing parameters include the machining voltage, the processing time, the machining gap, the electrolyte concentration, the additive agent concentration, pulse frequency and duty factor, etc. The result of experiments reveals that appropriate concentrations of ethanol can expand the size of the pores and enhance surface roughening effect. The appropriate processing parameters are a machining gap of 200μm, voltage of 48V, concentration of potassium hydroxide of 3M, concentration of ethanol of 4%. The electrochemical discharge machined surface roughness was increased from 0.417μm to 0.915μm using one minute processing time. The average reflectance rate of the textured surface was decreased from 29.6% to 12.7%. This study reveals that ECDM method has the advantage of short processing time and can generate a higher surface roughness and the porous structure.

Development of eco-friendly cleaning solution for industrial silicon wafer solar cell

In the cleaning process to fabricate silicon solar cell wafers, removal of stains and metal impurities on the wafer surface is important since they can affect the surface texturing of silicon solar cells. The surfactants included in a cleaning solution used for the cleaning process have a significant effect on the detergency by slightly altering the temperature, concentration, or molecular structure of the adsorbent. In this study, the eco-friendly and reusable cleaning solution have been developed to remove the generation of stains and increase the recyclability of the cleaning solution by adjusting the ratio of polyoxyethylene lauryl ether, which is a nonionic surfactant with several advantages such as, no ion pollution and strong osmosis. The stain inspection revealed that the generation rate of stains reduced from 0.35% to 0.01% when the ratio of the polyoxyethylene lauryl ether included in the cleaning solution was the highest. It was confirmed that the cleaning solution with the highest ratio of polyoxyethylene lauryl ether can be reused over 60 times by the investigation of the concentration of metal impurities, the texturing result and the reflectance values. The cleaning solution with the highest ratio of the polyoxyethylene lauryl ether is the most suitable for the mass-production process, owing to the low generation rate of stains and re-useable solution.

Silicon ingot casting using reusable silicon nitride crucibles made from diamond wire sawing kerf-loss silicon

The production of silicon wafers for solar cells generates two major solid wastes. One is the broken quartz crucibles after crystal growth, and the other is the kerf-loss silicon during wafer sawing. In this study, we demonstrated that the reaction bonded silicon nitride crucibles made from the acid leached kerf-loss silicon could be used for silicon casting. The ingots grown from the silicon nitride crucibles had better minority carrier lifetime than that grown from the quartz crucibles; the interstitial oxygen was significantly lower as well. The nitride crucible was reused at least 4 times and remained almost intact.

Comparative study of different silicon oxides used as interfacial passivation layer (SiNy:H / SiOx /n+-Si) in industrial monocrystalline silicon solar cells

Ultrathin silicon oxide (SiOx) is used as a passivating and tunneling layer in high efficiency passivated contact silicon (Si) wafer solar cells. In this work, the emitter surface passivation quality using a low-cost, low-temperature (40 °C), non-acidic and safe chemical oxide passivation process (named as NCPRE-oxide) grown using sodium hypochlorite solution is compared with other existing oxide growth or deposition processes such as dry thermal oxide, Radio Corporation of America standard clean-2 (RCA-2) chemical oxide, nitric acid based oxide, sulphuric acid based (Piranha) oxide, ozone based oxide and deposited oxide by plasma enhanced chemical vapour deposition on standard 6-inch textured Si wafers. All the oxides layers are capped with hydrogenated amorphous silicon nitride (SiNy:H) improve passivation of the n+-type Si surface. There is a substantial improvement in the effective minority carrier lifetime (τeff) for SiOx/SiNy:H stack on the phosphorous diffused pyramidal textured Si surface. Further, to compare the influence of NCPRE-oxide process with other oxide processes on the electrical performance of the final device, these different processes were included in the fabrication of large area industrial aluminum-back surface field (Al-BSF) solar cells. A comprehensive analysis based on ellipsometry for film thickness measurement, τeff measurement, cell current-voltage characteristics, photoluminescence imaging, internal quantum efficiency mapping, and front surface recombination velocity measurement is presented. The NCPRE-oxide process resulted in a similar improvement in passivation and cell efficiency as other oxide processes for Al-BSF cells. In addition, its low-cost, low thermal budget, easy waste disposal, and single-component nature make it viable for industrial scale implementation.