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.

Calculated and Experimental Research of Sheet Resistances of Laser-Doped Silicon Solar Cells

The calculated and experimental research of sheet resistances of crystalline silicon solar cells by dry laser doping is investigated. The nonlinear numerical model on laser melting of crystalline silicon and liquid-phase diffusion of phosphorus atoms by dry laser doping is analyzed by the finite difference method implemented in MATLAB. The melting period and melting depth of crystalline silicon as a function of laser energy density is achieved. The effective liquid-phase diffusion of phosphorus atoms in melting silicon by dry laser doping is confirmed by the rapid decrease of sheet resistances in experimental measurement. The plateau of sheet resistances is reached at around 15 Ω/. The calculated sheet resistances as a function of laser energy density is obtained and the calculated results are in good agreement with the corresponding experimental measurement. Due to the successful verification by comparison between experimental measurement and calculated results, the simulation results could be used to optimize the virtual laser doping parameters.

Detection of finger interruptions in silicon solar cells using photoluminescence imaging

Finger interruptions are common problems in screen printed solar cells, resulting in poor performance in efficiency because of high effective series resistance. Electroluminescence（EL） imaging is typically used to identify interrupted fingers. In this paper, we demonstrate an alternative method based on photoluminescence（PL） imaging to identify local series resistance defects, with a particular focus on finger interruptions. Ability to detect finger interruptions by using PL imaging under current extraction is analyzed and verified. The influences of external bias control and illumination intensity on PL images are then studied in detail. Finally, in comparison with EL imaging, the using of PL imaging to identify finger interruptions possesses the prominent advantages： in PL images, regions affected by interrupted fingers show higher luminescence intensity, while regions affected by recombination defects show lower luminescence intensity. This inverse signal contrast allows PL imaging to more accurately identify the defect types.

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.

The 18.3% Silicon Solar Cells with Nano-Structured Surface and Rear Emitter

A nano-structured surface is formed on the pyramid structure of n-type silicon solar cells by size-controlled silver nano-particle assisted etching. Such a nano-structure creates a front average weighted reflectance of less than 2.5% in the 300-1200nm range due to the broadband reflection suppression. The sodium hydroxide is used to obtain the low-area surface by post-etching the nano-structure, thus the severe carrier recombination associated with the nano-structured surface could be reduced. After emitter forming, screen printing and firing by means of the industrial fabrication protocol, an 18.3%-efficient nano-structured silicon solar cell with rear emitter is fabricated. The process of fabricating the solar cells matches well with industrial manufacture and shows promising prospects.

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.

Design of advanced porous silver powder with high-sintering activity to improve silicon solar cells

Silver(Ag)paste is widely used in semiconductor metallization,especially in silicon solar cells.Ag powder is the material with the highest proportion in Ag paste.The morphology and structure of Ag powder are crucial which determine its characteristics,especially for the sintering activity.In this work,a simple method was developed to synthesize a type of microcrystalline spherical Ag particles(SP-A)with internal pores and the structural changes and sintering behavior were thoroughly studied by combining ultra-small-angle X-ray scattering(USAXS),small-angle X-ray scattering(SAXS),in-situ heating X-ray diffraction(XRD),focused ion beam(FIB),and thermal analysis measurement.Due to the unique internal pores,the grain size of SP-A is smaller,and the coefficient of thermal expansion(CTE)is higher than that of traditional solid Ag particles.As a result,the sintering activity of SP-A is excellent,which can form a denser sintered body and form silver nanoparticles at the Ag–Si interface to improve silver silicon contact.Polycrystalline silicon solar cell built with SP-A obtained a low series resistance(Rs)and a high photoelectric conversion efficiency(PCE)of 19.26%.These fill a gap in Ag particle structure research,which is significant for the development of high-performance electronic Ag particles and efficient semiconductor devices.

Maskless fabrication of quasi-omnidirectional V-groove solar cells using an alkaline solution-based method

Silicon passivated emitter and rear contact(PERC) solar cells with V-groove texture were fabricated using maskless alkaline solution etching with in-house developed additive. Compared with the traditional pyramid texture, the V-groove texture possesses superior effective minority carrier lifetime, enhanced p–n junction quality and better applied filling factor(FF). In addition, a V-groove texture can greatly reduce the shading area and edge damage of front Ag electrodes when the V-groove direction is parallel to the gridline electrodes. Due to these factors, the V-groove solar cells have a higher efficiency(21.78%) than pyramid solar cells(21.62%). Interestingly, external quantum efficiency(EQE) and reflectance of the V-groove solar cells exhibit a slight decrease when the incident light angle(θ) is increased from 0° to 75°, which confirms the excellent quasi omnidirectionality of the V-groove solar cells. The proposed V-groove solar cell design shows a 2.84% relative enhancement of energy output over traditional pyramid solar cells.

Improving the UV-light stability of silicon heterojunction solar cells through plasmon-enhanced luminescence downshifting of YVO_(4):Eu^(3+),Bi^(3+)nanophosphors decorated with Ag nanoparticles

The ultraviolet(UV)light stability of silicon heterojunction(SHJ)solar cells should be addressed before large-scale production and applications.Introducing downshifting(DS)nanophosphors on top of solar cells that can convert UV light to visible light may reduce UV-induced degradation(UVID)without sacrificing the power conversion efficiency(PCE).Herein,a novel composite DS nanomaterial composed of YVO_(4):Eu^(3+),Bi^(3+)nanoparticles(NPs)and AgNPs was synthesized and introduced onto the incident light side of industrial SHJ solar cells to achieve UV shielding.The YVO_(4):Eu^(3+),Bi^(3+)NPs and Ag NPs were synthesized via a sol-gel method and a wet chemical reduction method,respectively.Then,a composite structure of the YVO_(4):Eu^(3+),Bi^(3+)NPs decorated with Ag NPs was synthesized by an ultrasonic method.The emission intensities of the YVO_(4):Eu^(3+),Bi^(3+)nanophosphors were significantly enhanced upon decoration with an appropriate amount of~20 nm Ag NPs due to the localized surface plasmon resonance(LSPR)effect.Upon the introduction of LSPR-enhanced downshifting,the SHJ solar cells exhibited an~0.54%relative decrease in PCE degradation under UV irradiation with a cumulative dose of 45 k W h compared to their counterparts,suggesting excellent potential for application in UV-light stability enhancement of solar cells or modules.

Efficiency-loss analysis of monolithic perovskite/silicon tandem solar cells by identifying the patterns of a dual two-diode model’s current-voltage curves

In this work,we developed a simple and direct circuit model with a dual two-diode model that can be solved by a SPICE numerical simulation to comprehensively describe the monolithic perovskite/crystalline silicon(PVS/c-Si)tandem solar cells.We are able to reveal the effects of different efficiency-loss mechanisms based on the illuminated current density-voltage(J-V),semi-log dark J-V,and local ideality factor(m-V)curves.The effects of the individual efficiency-loss mechanism on the tandem cell’s efficiency are discussed,including the exp(V/VT)and exp(V/2VT)recombination,the whole cell’s and subcell’s shunts,and the Ohmic-contact or Schottky-contact of the intermediate junction.We can also fit a practical J-V curve and find a specific group of parameters by the trial-and-error method.Although the fitted parameters are not a unique solution,they are valuable clues for identifying the efficiency loss with the aid of the cell’s structure and experimental processes.This method can also serve as an open platform for analyzing other tandem solar cells by substituting the corresponding circuit models.In summary,we developed a simple and effective methodology to diagnose the efficiency-loss source of a monolithic PVS/c-Si tandem cell,which is helpful to researchers who wish to adopt the proper approaches to improve their solar cells.

Polarization effects and tests for crystalline silicon solar cells

We try to find a fast and simple potential induced degradation effect （PID） test procedure for crystalline silicon solar cells. With sodium chloride （NaC1） solution as Na＋ source, PVB as lamination material, we can carry out the test in 1 h. Solar cells with newly developed PID resistance process were also tested. The increase of reverse current of solar cell can be considered a key standard to determine if the solar cell was prone to PID. Moreover, it showed that the increase of reverse current for the PID resistance solar cell was less than 2. In addition, the test results of the solar cells fitted very well with that of the modules by standard procedure.

Influence of atomic layer deposition Al_2O_3 nano-layer on the surface passivation of silicon solar cells

A stack of Al2O3/SiNx dual layer was applied for the back side surface passivation of p-type multi-crystalline silicon solar cells, with laser-opened line metal contacts, forming a local aluminum back surface field （local Al-BSF） structure. A slight amount of Al2O3, wrapping around to the front side of the wafer during the thermal atomic layer deposition process, was found to have a negative influence on cell performance. The different process flow was found to lead to a different cell performance, because of the Al2O3 wrapping around the front surface. The best cell performance, with an absolute efficiency gain of about 0.6% compared with the normal full Al-BSF structure solar cell, was achieved when the Al2O3 layer was deposited after the front surface of the wafer had been covered by a SiNx layer. We discuss the possible reasons for this phenomenon, and propose three explanations as the Ag paste, being hindered from firing through the front passivation layer, degraded the SiNx passivation effect and the Al2O3 induced an inversion effect on the front surface. Characterization methods like internal quantum efficiency and contact resistance scanning were used to assist our understanding of the underlying mechanisms.

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.

Low Energy H^+ Effects on the Photovoltaic and Optical Properties of Polycrystalline Silicon Solar Cells

Low energy hydrogen ion was used to passivate the electrically active defects existing in grains and grain boundaries of polycrystalline silicon solar cells.Short circuit current of H + implanted cells remarkably increased before and after preparing TiO 2AR(antireflective)coating.The measurements(at λ=6328) of the optical properties of H + implanted silicon samples show that:the value of absorption coefficient reached the level of a Si;refractive index n and reflectivity R significantly decreased;the optical band gap increased from 1.1 eV to 1.3 eV.The results indicate that Si H bonds have been formed after H + implantation.The calculation shows that the optical thickness cycle of TiO 2 AR coating will reduce correspondingly in order to obtain the optimum optical match between AR coating and implanted silicon since refractive index decreases after H + implantation.

Pulsed Laser Annealed Ga Hyperdoped Poly-Si/SiO_(x)Passivating Contacts for High-Efficiency Monocrystalline Si Solar Cells

Polycrystalline Si(poly-Si)-based passivating contacts are promising candidates for high-efficiency crystalline Si solar cells.We show that nanosecond-scale pulsed laser melting(PLM)is an industrially viable technique to fabricate such contacts with precisely controlled dopant concentration profiles that exceed the solid solubility limit.We demonstrate that conventionally doped,hole-selective poly-Si/SiO_(x)contacts that provide poor surface passivation of c-Si can be replaced with Ga-or B-doped contacts based on non-equilibrium doping.We overcome the solid solubility limit for both dopants in poly-Si by rapid cooling and recrystallization over a timescale of∼25 ns.We show an active Ga dopant concentration of∼3×10^(20)cm^(−3)in poly-Si which is six times higher than its solubility limit in c-Si,and a B dopant concentration as high as∼10^(21) cm^(−3).We measure an implied open-circuit voltage of 735 mV for Ga-doped poly-Si/SiO_(x)contacts on Czochralski Si with a low contact resistivity of 35.5±2.4 mΩcm^(2).Scanning spreading resistance microscopy and Kelvin probe force microscopy show large diffusion and drift current in the p-n junction that contributes to the low contact resistivity.Our results suggest that PLM can be extended for hyperdoping of other semiconductors with low solubility atoms to enable high-efficiency devices.

Determination of the Base Optimum Thickness of Back Illuminated (n+/p/p+) Bifacial Silicon Solar Cell, by Help of Diffusion Coefficient at Resonance Frequency

The bifacial silicon solar cell subjected to a magnetic field, is illuminated by the back side by a monochromatic light in frequency modulation, with high absorption, At minority carriers diffusion coefficient resonance frequency, a graphical study of the expressions of recombination velocity on the rear side is carried out. The optimum thickness of the base of the bifacial solar cell is deduced for each resonance frequency.

AC Back Surface Recombination Velocity as Applied to Optimize the Base Thickness under Temperature of an (n+-p-p+) Bifacial Silicon Solar Cell, Back Illuminated by a Light with Long Wavelength

The bifacial silicon solar cell, placed at temperature (T) and illuminated from the back side by monochromatic light in frequency modulation (ω), is studied from the frequency dynamic diffusion equation, relative to the density of excess minority carriers in the base. The expressions of the dynamic recombination velocities of the minority carriers on the rear side of the base Sb1(D(ω, T);H) and Sb2(α, D(ω, T);H), are analyzed as a function of the dynamic diffusion coefficient (D(ω, T)), the absorption coefficient (α(λ)) and the thickness of the base (H). Thus their graphic representation makes it possible to go up, to the base optimum thickness (Hopt(ω, T)), for different temperature values and frequency ranges of modulation of monochromatic light, of strong penetration. The base optimum thickness (Hopt(ω, T)) decreases with temperature, regardless of the frequency range and allows the realization of the solar cell with few material (Si).

Influence of band gap of p-type hydrogenated nanocrystalline silicon layer on the short-circuit current density in thin-film silicon solar cells

The impact of the optical band gap（Eg） of a p-type hydrogenated nanocrystalline silicon layer on the short-circuit current density（Jsc） of a thin-film silicon solar cell is assessed. We have found that the Jsc reaches maximum when the Eg reaches optimum. The reason for the Jsc on Eg needs to be clarified. Our results exhibit that maximum Jsc is the balance between dark current and photocurrent. We show here that this dark current results from the density of defects in the p-layer and the barrier at the interface between p-and i-layers. An optimum cell can be designed by optimizing the p-layer via reducing the density of defects in the p-layer and the barrier at the p/i interface. Finally, a 6.6% increase in Jsc was obtained at optimum Eg for n-i-p solar cells.

Detailed balance limit efficiency of silicon intermediate band solar cells

The detailed balance method is used to study the potential of the intermediate band solar cell （IBSC）, which can improve the efficiency of the gi-based solar cell with a bandgap between 1.1 eV to 1.7 eV. It shows that a crystalline silicon solar ceil with an intermediate band located at 0.36 eV below the conduction band or above the valence band can reach a limiting efficiency of 54% at the maximum light concentration, improving greatly than 40.7% of the Shoekley-Queisser limit for the single junction Si solar cell. The simulation also shows that the limiting efficiency of the silicon-based solar cell increases as the bandgap increases from 1.1 eV to 1.7 eV, and the amorphous Si solar cell with a bandgap of 1.7 eV exhibits a radiative limiting efficiency of 62.47070, having a better potential.

Texturization of mono-crystalline silicon solar cells in TMAH without the addition of surfactant

Etching was performed on （100） silicon wafers using silicon-dissolved tetramethylammonium hydroxide （TMAH） solutions without the addition of surfactant. Experiments were carried out in different TMAH concentrations at different temperatures for different etching times. The surface phenomena, etching rates, surface morphology and surface reflectance were analyzed. Experimental results show that the resulting surface covered with uniform pyramids can be realized with a small change in etching rates during the etching process. The etching mechanism is explained based on the experimental results and the theoretical considerations. It is suggested that all the components in the TMAH solutions play important roles in the etching process. Moreover, TMA^＋ ions may increase the wettability of the textured surface. A good textured surface can be obtained in conditions where the absorption of OH-/H2O is in equilibrium with that of TMA＋/SiO2（OH）2^-.