Textured Perovskite/Silicon Tandem Solar Cells Achieving Over 30% Efficiency Promoted by 4-Fluorobenzylamine Hydroiodide

Monolithic textured perovskite/silicon tandem solar cells(TSCs)are expected to achieve maximum light capture at the lowest cost,potentially exhibiting the best power conversion efficiency.However,it is challenging to fabricate high-quality perovskite films and preferred crystal orientation on commercially textured silicon substrates with micrometersize pyramids.Here,we introduced a bulky organic molecule(4-fluorobenzylamine hydroiodide(F-PMAI))as a perovskite additive.It is found that F-PMAI can retard the crystallization process of perovskite film through hydrogen bond interaction between F^(−)and FA^(+)and reduce(111)facet surface energy due to enhanced adsorption energy of F-PMAI on the(111)facet.Besides,the bulky molecular is extruded to the bottom and top of perovskite film after crystal growth,which can passivate interface defects through strong interaction between F-PMA+and undercoordinated Pb^(2+)/I^(−).As a result,the additive facilitates the formation of large perovskite grains and(111)preferred orientation with a reduced trap-state density,thereby promoting charge carrier transportation,and enhancing device performance and stability.The perovskite/silicon TSCs achieved a champion efficiency of 30.05%based on a silicon thin film tunneling junction.In addition,the devices exhibit excellent longterm thermal and light stability without encapsulation.This work provides an effective strategy for achieving efficient and stable TSCs.

Corrective Effect of the Angle of Incidence of the Magnetic Field Intensity on the Performance (Series and Shunt Resistances) of a Bifacial Silicon Solar Cell

This article presents a three-dimensional analysis of the impact of the angle of incidence of the magnetic field intensity on the electrical performance (series resistance, shunt resistance) of a bifacial polycrystalline silicon solar cell. The cell is illuminated simultaneously from both sides. The continuity equation for the excess minority carriers is solved at the emitter and at the depth of the base respectively. The analytical expressions for photocurrent density, photovoltage, series resistance and shunt resistance were deduced. Using these expressions, the values of the series and shunt resistances were extracted for different values of the angle of incidence of the magnetic field intensity. The study shows that as the angle of incidence increases, the slopes of the minority carrier density for the two modes of operation of the solar cell decrease. This is explained by a drop in the accumulation of carriers in the area close to the junction due to the fact that the Lorentz force is unable to drive the carriers towards the lateral surfaces due to the weak action of the magnetic field, which tends to cancel out as the incidence angle increases, and consequently a drop in the open circuit photovoltage. This, in turn, reduces the Lorentz force. These results predict that the p-n junction of the solar cell will not heat up. The study also showed a decrease in series resistance as the incidence angle of the magnetic field intensity increased from 0 rad to π/2 rad and an increase in shunt resistance as the incidence angle increased. His behaviour of the electrical parameters when the angle of incidence of the field from 0 rad to π/2 rad shows that the decreasing magnetic field vector tends to be collinear with the electron trajectory. This allows them to cross the junction and participate in the external current. The best orientation for the Lorentz force is zero, in which case the carriers can move easily towards the junction.

Modeling and Simulation of Heterojunction Solar Cell with Mono Crystalline Silicon

The monocrystalline silicon is a promising material that could be used in solar cells that convert light into electricity. Although the cost of ordinary silicon (Si) solar cells has decreased significantly over the past two decades, the conversion efficiency of these cells has remained relatively high. While solar cells have a great potential as a device of renewable energy, the high cost they incur per Watt continues to be a significant barrier to their widespread implementation. As a consequence, it is vital to conduct research into alternate materials that may be used in the construction of solar cells. The heterojunction solar cell (HJSC), which is based on n-type zinc oxide (n-ZnO) and p-type silicon (p-Si), is one of the numerous alternatives of the typical Si single homojunction solar cell. There are many deficiencies that can be found in the published research on n-ZnO/p-Si heterojunction solar cell. Inconsistencies in the stated value of open circuit voltage (Voc) of the solar cell are one example of deficiency. The absence of a full theoretical study to evaluate the potential of the solar cell structure is another deficiency that can be found in these researches. A lower value of experimentally obtained VOC in comparison to the theoretical prediction based on the band-gap between n-ZnO and p-Si. There needs to be more consensus among scientists regarding the optimal conditions for the growth of zinc oxide. Many software’s are available for simulating and optimizing the solar cells based on these parameters. For this purpose, in this dissertation, I provide computational results relevant to n-ZnO/p-Si HJSC to overcome deficiencies that have been identified. While modeling and simulating the potential of the solar cell structure with AFORS-HET, it is essential to consider the constraints that exist in the real world. AFORS-HET was explicitly designed to mimic the multilayer solar cell arrangement. In AFORS-HET, we can add up to seven layers for solar cell layout. By using this software, we can figure out the open circuit voltage (VOC), the short circuit current (JSC), the quantum efficiency (QE, %), the heterojunction energy band structure, and the power conversion efficiency (PCE).

Preparation, microstructure and dislocation of solar-grade multicrystalline silicon by directional solidification from metallurgical-grade silicon

A vacuum directional solidification with high temperature gradient was performed to prepare low cost solar-grade multicrystalline silicon （mc-Si） directly from metallurgical-grade mc-Si. The microstructure characteristic, grain size, boundary, solid-liquid growth interface, and dislocation structure under different growth conditions were studied. The results show that directionally solidified multicrystalline silicon rods with high density and orientation can be obtained when the solidification rate is below 60 μm/s. The grain size gradually decreases with increasing the solidification rate. The control of obtaining planar solid-liquid interface at high temperature gradient is effective to produce well-aligned columnar grains along the solidification direction. The growth step and twin boundaries are preferred to form in the microstructure due to the faceted growth characteristic of mc-Si. The dislocation distribution is inhomogeneous within crystals and the dislocation density increases with the increase of solidification rate. Furthermore, the crystal growth behavior and dislocation formation mechanism of mc-Si were discussed.

Electrical conductivity and viscosity of cryolite electrolytes for solar grade silicon(Si-SoG) electrowinning

Electrical conductivity of molten binary and ternary mixtures based on the system NaF-AlF3-SiO2 was investigated by means of a tube–cell （made of pyrolytic boron nitride） with stationary electrodes. Viscosity of the binary system Na3AlF6-SiO2 was measured by computerized torsion pendulum method. It was found that conductivity and viscosity varied linearly with temperature in all investigated mixtures. Obtained content dependence of electrical conductivity （isotherms） was divided into two parts. First, one represented the content region up to 10%（mole fraction） of SiO2;second, the region was with a higher content of SiO2 （from 10%up to 40%）. While the conductivity considerably decreased with content of SiO2 in the second part; it surprisingly rose in the low content range. A small addition of SiO2 to the molten cryolite （up to 10%） could slightly increase viscosity, but had no influence on the slope of this dependence since it is responsible for a glassy-networks formation in the melt. Further addition of SiO2 to the molten cryolite had a huge effect on the viscosity.

Purification of solar cell silicon materials through filtration

Silicon is the material most commonly used in the manufacturing of photovoltaic (PV) cells. In the current study, laboratory experiments of purification of solar cell silicon materials through filtration are carried out. Inclusion removal from silicon was investigated. The purpose is to achieve clean silicon materials for solar cells. Silicon samples and filter samples were analyzed using microscope observation, EPMA, and X-ray detection. Silicon nitride (Si3N4) and silicon carbide (SiC) particles are the main non-metallic inclusions present in top-cut silicon scrap. Almost all inclusions larger than 10 μm can be removed from silicon by the porous foam filter. In mass fraction, more than 90% inclusions are removed. Si3N4 particles are mainly removed on the top surface of the filter, and SiC particles are mainly removed by entering the pores and attaching to the filter material. SiC inclusions are not only simply attached on the surface of the filter material, but are found also inside the filter material. There are SiC bridges near the filter materials. These bridges may fill the spaces between filter material, and this will further retard inclusions passing through the filter. Three-dimensional turbulent fluid flow and inclusion motion in the filter was calculated. Both experimental observation and fluid flow simulation indicate that most of the inclusions are entrapped at the upper part of the filter.

Improvement in IBC-silicon solar cell performance by insertion of highly doped crystalline layer at heterojunction interfaces

By inserting a thin highly doped crystalline silicon layer between the base region and amorphous silicon layer in an interdigitated back-contact （IBC） silicon solar cell, a new passivation layer is investigated. The passivation layer performance is characterized by numerical simulations. Moreover, the dependence of the output parameters of the solar cell on the additional layer parameters （doping concentration and thickness） is studied. By optimizing the additional passivation layer in terms of doping concentration and thickness, the power conversion efficiency could be improved by a factor of 2.5%, open circuit voltage is increased by 30 mV and the fill factor of the solar cell by 7.4%. The performance enhancement is achieved due to the decrease of recombination rate, a decrease in solar cell resistivity and improvement of field effect passivation at heterojunction interface. The above-mentioned results are compared with reported results of the same conventional interdigitated back-contact silicon solar cell structure. Furthermore, the effect of a-Si：H/c-Si interface defect density on IBC silicon solar cell parameters with a new passivation layer is studied. The additional passivation layer also reduces the sensitivity of output parameter of solar cell to interface defect density.

Photocarrier radiometry for noncontact evaluation of space monocrystalline silicon solar cell under low-energy electron irradiation

A space monocrystalline silicon（c-Si） solar cell under low-energy（〈 1 MeV） electron irradiation was investigated using noncontact photocarrier radiometry（PCR）. Monte Carlo simulation（MCS） was employed to characterize the effect of different energy electron irradiation on the c-Si solar cell. The carrier transport parameters（carrier lifetime, diffusion coefficient, and surface recombination velocities） were obtained by best fitting the experimental results with a theoretical one-dimensional two-layer PCR model. The results showed that the increase of the irradiation electron energy caused a large reduction of the carrier lifetime and diffusion length. Furthermore, the rear surface recombination velocity of the Si：p base of the solar cell at the irradiation electron energy of 1 Me V was dramatically enhanced due to 1 MeV electron passing through the whole cell. Short-circuit current（I sc） degradation evaluated by PCR was in good agreement with that obtained by electrical measurement.

Simulation and experimental study of a novel bifacial structure of silicon heterojunction solar cell for high efficiency and low cost

A novel structure of Ag gridlSiN_(x)/n+-c-Si/n-c-Si/i-a-Si:H/p^(+)-a-Si:HlTCO/Ag grid was designed to increase the ef-ficiency of bifacial amorphous/crystalline silicon-based solar cells and reduce the rear material consumption and production cost.The simulation results show that the new structure obtains higher efficiency compared with the typical bifa-cial amorphous/crystalline silicon-based solar cell because of an increase in the short-circuit current(J_(sc)),while retaining the advantages of a high open-circuit voltage,low temperature coefficient,and good weak-light performance.Moreover,real cells composed of the novel structure with dimensions of 75 mm×75 mm were fabricated by a special fabrication recipe based on industrial processes.Without parameter optimization,the cell efficiency reached 21.1%with the J_(sc)of 41.7 mA/cm^(2).In addition,the novel structure attained 28.55%potential conversion efficiency under an illumination of AM 1.5 G,100 mW/cm^(2).We conclude that the configuration of the Ag grid/SiN_(x)/n^(+)-c-Si/n-c-Si/i-a-Si:H/p^(+)-a-Si:H/TCO/Ag grid is a promising structure for high efficiency and low cost.

Back Surface Recombination Velocity Dependent of Absorption Coefficient as Applied to Determine Base Optimum Thickness of an n+/p/p+ Silicon Solar Cell

The monochromatic absorption coefficient of silicon, inducing the light penetration depth into the base of the solar cell, is used to determine the optimum thickness necessary for the production of a large photocurrent. The absorption-generation-diffusion and recombination (bulk and surface) phenomena are taken into account in the excess minority carrier continuity equation. The solution of this equation gives the photocurrent according to absorption and electronic parameters. Then from the obtained short circuit photocurrent expression, excess minority carrier back surface recombination velocity is determined, function of the monochromatic absorption coefficient at a given wavelength. This latter plotted versus base thickness yields the optimum thickness of an n+-p-p+ solar cell, for each wavelength, which is in the range close to the energy band gap of the silicon material. This study provides a tool for improvement solar cell manufacture processes, through the mathematical relationship obtained from the thickness limit according to the absorption coefficient that allows base width optimization.

Enhanced Photovoltaic Properties for Rear Passivated Crystalline Silicon Solar Cells by Fabricating Boron Doped Local Back Surface Field

In order to enhance the p-type doping concentration in the LBSF, boron was added into the aluminum paste and boron doped local back surface field（B-LBSF） was successfully fabricated in this work. Through boron doping in the LBSF, much higher doping concentration was observed for the B-LBSF over the Al-LBSF. Higher doping concentration in the LBSF is expected to lead to better rear passivation and lower rear contact resistance. Based on one thousand pieces of solar cells for each type, it was found that the rear passivated crystalline silicon solar cells with B-LBSF showed statistical improvement in their photovoltaic properties over those with Al-LBSF.

Numerical study of mono-crystalline silicon solar cells with passivated emitter and rear contact configuration for the efficiency beyond 24% based on mass production technology

Mono-crystalline silicon solar cells with a passivated emitter rear contact(PERC)configuration have attracted extensive attention from both industry and scientific communities.A record efficiency of 24.06%on p-type silicon wafer and mass production efficiency around 22%have been demonstrated,mainly due to its superior rear side passivation.In this work,the PERC solar cells with a p-type silicon wafer were numerically studied in terms of the surface passivation,quality of silicon wafer and metal electrodes.A rational way to achieve a 24%mass-production efficiency was proposed.Free energy loss analyses were adopted to address the loss sources with respect to the limit efficiency of 29%,which provides a guideline for the design and manufacture of a high-efficiency PERC solar cell.

Influence of texture feature size on spherical silicon solar cells

The effects of surface texturing on spherical silicon solar cells were investigated. Surface texturing for spherical Si solar cells was prepared by immersing p-type spherical Si crystals in KOH solution with stirring. Two kinds of texture feature sizes (1 and 5 μm pyramids) were prepared by changing stirring speed. After fabrication through our baseline processes, these cells were evaluated by solar cell performance and external quantum efficiency. The cell with 1 and 5 μm pyramids shows the short circuit current density (Jsc) value of 31.9 and 33.2 mA·cm-2, which is 9% and 13% relative increase compared to the cell without texturing. Furthermore, the cell with 5 μm pyramids has a higher open-circuit voltage (0.589 V) than the cell with 1 μm pyramids (0.577 V). As a result, the conversion efficiency was improved from 11.4% for the cell without texturing to 12.1% for the cell with 5 μm pyramids.

External Magnetic Field Effect on Bifacial Silicon Solar Cell’s Electrical Parameters

The aim of this work is to present a theoretical study of external magnetic field effect on a bifacial silicon solar cell’s electrical parameters (peak power, fill factor and load resistance) using the J-V and P-V characteristics. After the resolution of the magneto transport equation and continuity equation of excess minority carriers in the base of the bifacial silicon solar cell under multispectral illumination, the photo-current density and the photovoltage are determined and the J-V and P-V curves are plotted. Using simultaneously the J-V and P-V curves, we determine, according to magnetic field intensity, the peak photocurrent density, the peak photovoltage, the peak electric power, the fill factor and the load resistance at the peak power point. The numerical data show that the solar cell’s peak power decreases with magnetic field intensity while the fill factor and the load resistance increase.

Review on Metallization Approaches for High-Efficiency Silicon Heterojunction Solar Cells

Crystalline silicon(c-Si)heterojunction(HJT)solar cells are one of the promising technologies for next-generation industrial high-efficiency silicon solar cells,and many efforts in transferring this technology to high-volume manufacturing in the photovoltaic(PV)industry are currently ongoing.Metallization is of vital importance to the PV performance and long-term reliability of HJT solar cells.In this review,we summarize the development status of metallization approaches for highefficiency HJT solar cells.For conventional screen printing technology,to avoid the degradation of the passivation properties of the amorphous silicon layer,a low-temperature-cured(<250℃)paste and process are needed.This process,in turn,leads to high line/contact resistances and high paste costs.To improve the conductivity of electrodes and reduce the metallization cost,multi-busbar,fine-line printing,and low-temperature-cured silver-coated copper pastes have been developed.In addition,several potential metallization technologies for HJT solar cells,such as the Smart Wire Contacting Technology,pattern transfer printing,inkjet/FlexTrailprinting,and copper electroplating,are discussed in detail.B ased on the summary,the potential and challenges of these metallization technologies for HJT solar cells are analyzed.

A.C. Recombination Velocity as Applied to Determine n⁺/p/p⁺Silicon Solar Cell Base Optimum Thickness

This work deals with determining the optimum thickness of the base of an n+/p/p+ silicon solar cell under monochromatic illumination in frequency modulation. The continuity equation for the density of minority carriers generated in the base, by a monochromatic wavelength illumination (λ), with boundary conditions that impose recombination velocities (Sf) and (Sb) respectively at the junction and back surface, is resolved. The ac photocurrent is deduced and studied according to the recombination velocity at the junction, to extract the mathematical expressions of recombination velocity (Sb). By the graphic technique of comparing the two expressions obtained, depending on the thickness (H) of the base, for each frequency, the optimum thickness (Hopt) is obtained. It is then modeled according to the frequency, at the long wavelengths of the incident light. Thus, Hopt decreases due to the low relaxation time of minority carriers, when the frequency of modulation of incident light increases.

Beyond Lambertian light trapping for large-area silicon solar cells:fabrication methods

Light trapping photonic crystal(PhC)patterns on the surface of Si solar cells provides a novel opportunity to approach the theoretical efficiency limit of 32.3%,for light-to-electrical power conversion with a single junction cell.This is beyond the efficiency limit implied by the Lambertian limit of ray trapping~29%.The interference and slow light effects are harnessed for collecting light even at the long wavelengths near the Si band-gap.We compare two different methods for surface patterning,that can be extended to large area surface patterning:1)laser direct write and 2)step-&-repeat 5×reduction projection lithography.Large area throughput limitations of these methods are compared with the established elec-tron beam lithography(EBL)route,which is conventionally utilised but much slower than the presented methods.Spec-tral characterisation of the PhC light trapping is compared for samples fabricated by different methods.Reflectance of Si etched via laser patterned mask was~7%at visible wavelengths and was comparable with Si patterned via EBL made mask.The later pattern showed a stronger absorbance than the Lambertian limit6.

Back Illuminated N/P/P⁺Bifacial Silicon Solar Cell under Modulated Short-Wavelength: Determination of Base Optimum Thickness

A bifacial silicon solar cell under monochromatic illumination in frequency modulation by the rear side is being studied for the optimization of base thickness. The density of photogenerated carriers in the base is obtained by resolution of the continuity equation, with the help of boundary conditions at the junction surface (n+/p) and the rear face (p/p+) of the base. For a short wavelength corresponding to a high absorption coefficient, the AC photocurrent density is calculated and represented according to the excess minority carrier’s recombination velocity at the junction, for different modulation frequency values. The expression of the AC recombination velocity of excess minority carriers at the rear surface of the base of the solar cell is then deduced, depending on both, the absorption coefficient of the silicon material and the thickness of the base. Compared to the intrinsic AC recombination velocity, the optimal thickness is extracted and modeled in a mathematical relationship, as a decreasing function of the modulated frequency of back illumination. Thus under these operating conditions, a maximum short-circuit photocurrent is obtained and a low-cost bifacial solar cell can be achieved by reducing material (Si) to elaborate the base thickness.

n⁺-p-p⁺Silicon Solar Cell Base Optimum Thickness Determination under Magnetic Field

Base optimum thickness is determined for a front illuminated bifacial silicon solar cell n+-p-p+ under magnetic field. From the magneto transport equation relative to excess minority carriers in the base, with specific boundary conditions, the photocurrent is obtained. From this result the expressions of the carrier’s recombination velocity at the back surface are deducted. These new expressions of recombination velocity are plotted according to the depth of the base, to deduce the optimum thickness, which will allow the production, of a high short-circuit photocurrent. Calibration relationships of optimum thickness versus magnetic field were presented according to study ranges. It is found that, applied magnetic field imposes a weak thickness material for solar cell manufacturing leading to high short-circuit current.

Diffusion Coefficient at Resonance Frequency as Applied to n+/p/p+ Silicon Solar Cell Optimum Base Thickness Determination

The modelling and determination of the geometric parameters of a solar cell are important data, which influence the evaluation of its performance under specific operating conditions, as well as its industrial development for a low cost. In this work, an n+/p/p+ crystalline silicon solar cell is studied under monochromatic illumination in modulation and placed in a constant magnetic field. The minority carriers’ diffusion coefficient (D(ω, B), in the (p) base leads to maximum values (Dmax) at resonance frequencies (ωr). These values are used in expressions of AC minority carriers recombination velocity (Sb(Dmax, H)) in the rear of the base, to extract the optimum thickness while solar cell is subjected to these specific conditions. Optimum thickness modelling relationships, depending respectively on Dmax, ωr and B, are then established, and will be data for industrial development of low-cost solar cells for specific use.