Surface Of Si Solar Cells Research Articles

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 electron beam lithography (EBL) route, which is conventionally utilised but much slower than the presented methods. Spectral 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 limit. (M.-L. Hsieh et al., Sci. Rep. 10, 11857 (2020)).

Finding 10% hidden electricity in crystalline Si solar cells using PDMS coating and three‐dimensional cell arrays

AbstractOver the decades, solar cells have been developed to achieve higher energy conversion efficiency. However, the fabrication of modules has resulted in electricity production loss, but this has not attracted as much attention as the solar cells. As a result, the improved performance of solar cells has not been fully revealed at the panel scale. Furthermore, the standard testing conditions, such as 1 sun, AM1.5, which is very strong incident light, does not fully reflect the electricity production capabilities of solar panels because of performance degradation under oblique and weak illumination. Simple modification of the module fabrication process, including poly‐dimethylsiloxane (PDMS) coatings and three‐dimensional (3‐D) structured modules by one‐directional angled arrays of each cell, has revealed 13.4% extra hidden electricity in solar panels with some types of crystalline silicon (Si)‐based solar cells through high transmission to short wavelength light, recapture of the light reflected from Si solar cell surface textures by the PDMS coating and enhanced power production under oblique incident light or scattered light through a 3‐D module. Further studies to find hidden electricity should be followed by the development of solar cell device structures to improve electricity production, rather than being restricted to optimizing energy conversion efficiency.

Green mediated synthesis of plasmonic nanoparticle (Ag) for antireflection coating in bare mono silicon solar cell

Novelty of the present work is to investigate the efficiency of the antireflection property of green mediated synthesized plasmonic nanoparticle coated monocrystalline silicon (Si) solar cell. Green mediated synthesis of plasmonic silver (Ag) nanoparticles (NPs) was carried out using three different leaves extracts (Eucalyptus glopus, Azadirachta indica and Coriandrum sativum) and reported for the first time. The face centred cubic structure, crystalline nature and purity of the synthesized material were confirmed by powder X-ray diffraction studies. Fourier transform infrared spectrum shows the presence of various functional groups in the resultant material. The maximum absorbance observed around 400–460 nm reveal the characteristic absorbance of Ag NPs. The surface morphology of the synthesized Ag NPs was analyzed using atomic force microscopy. Ag NPs were coated as antireflective material on the monocrystalline Si solar cell surface and its performance was evaluated from the corresponding JV characteristics. The obtained photovoltaic performance was compared with bare Si for comparison purpose and it is observed that there is an enhanced performance in the photo-conversion efficiency of the Si solar cells.

Luminescent down shifting CdTe colloidal quantum dots for enhancing polycrystalline silicon solar cells

In this paper, CdTe quantum dots (QDs) with emission bands at 762 nm and 812 nm were investigated for their use in luminescent down shifting (LDS) layers. Spectral location of emission bands and quantum yield of luminescence of the QDs in solution proposed that they were suitable nanoparticles for inclusion in LDS layers. QDs were dispersed in poly (methylmethacrylate) (PMMA) polymer matrix and thin films were fabricated approximately of 70 microns. Significant solar cell efficiency enhancements (approximately 5%–10%) under normal (AM1.5, 25 °C) condition were observed after QDs doped PMMA coatings. The experimental results showed increments in the Voc from 478 to 541 mV, Isc from 35 to 42 mA, Jsc from 8.96 to 10.51 mA/sm2, FF from 69.1 to 77.3% and efficiency from 13.12 to 19.48%. PMMA thin film doped with CdTe QDs was spin-coated on the front surface of Si solar cell for enhancing the solar cell efficiency via photoluminescence (PL) conversion and antireflection effects.

Wavelength conversion of Yb3+-activated Y4CdMo3O16 from near UV-region to IR emission

Yb3+ (0.5–30 mol %) activated Y4CdMo3O16 phosphors have been prepared by the traditional solid-state reaction method. The phase formation was investigated by the XRD structural refinements. The surface properties of the powder phosphors were verified by SEM, TEM and EDS measurements. The optical properties were evaluated by the reflectance spectra, photoluminescence excitation and emission spectra, decay curves (lifetimes), and the absolute quantum efficiency (QE). Under the excitation of UV light, Yb3+-activated Y4CdMo3O16 shows the efficient near-infrared (NIR) emission bands (900–1100 nm), which is ascribed to the 2F5/2 → 2F7/2 transitions of Yb3+ ions. The NIR emission intensity shows a dependence on Yb3+ contents, which has an optimal doping of 25 mol %. The energy transfer (ET) from MoO4 to Yb3+ ions in the lattices was discussed. The NIR emission around 1000 nm just corresponds to the optical response of Si-based solar cells. Consequently, the efficiency could be enhanced by arranging luminescent layers mixed with Y4CdMo3O16:Yb3+ phosphors and transparent matrix in the front surface of Si solar cells.

(Invited) Design and Challenging Issues of Core/Shell Quantum Dots for Enhancing Power-Conversion-Efficiency in Si Solar-Cells

Enhancing the efficiency of commercial Si solar cells via quantum dots as an energy-down-shift layer is a new, straightforward, and cost-effective approach to utilize the wasted energy in the ultraviolet-light. Cd-based core/shell quantum dots have been used as an efficient energy-down-shift quantum dot layer on the front surface of Si solar cells to enhance their photovoltaic properties. Here, we describe the designing of energy-down-shift quantum dot layers using three types of Cd-based QDs, binary CdSe/ZnS, ternary Cd0.5Zn0.5S/ZnS, and Mn2+-doped Cd0.5Zn0.5S/ZnS QDs to enhance the short-circuit density by 6.18, 6.48, and 4.02%; thereby, the power conversion efficiency improved by 5.51, 6.40, and 3.22%, respectively, of Si solar cells. In addition, the technical and environmental challenges that limit their commercial applications for cost-effective and high-performance Si solar cells are discussed.

(Invited) Design and Challenging Issues of Core/Shell Quantum Dots for Enhancing Power-Conversion-Efficiency in Si Solar-Cells

For last several decade, although intensive researches has been conducted, the maximum power-conversion-efficiency (PCE) of Si solar cells has been economically limited to ~25%. Since Si solar cells absorbed mainly photons in visible wavelength, the silicon solar cells using energy-down-shift (EDS) mechanism has been recently proposed. Un-doped core/shell quantum dots such as CdSe/ZnS or Cd0.5Zn0.5S/ZnS have well demonstrated EDS by the Stokes shift of 52~127 nm and enhances ~1% of the PCE in the Si solar cells by implementing them on the Si solar-cell surface1. In addition, environment-safe InP/ZnS core/shell quantum dots well demonstrated the PCE enhancement of the Si solar cells. However, such small Stokes shift from core/shell quantum dots led the Si solar cell surface to resorb partially the emitting blue light so that the possible PCE enhancement would be limited to ~1%. Recently, the higher than ~200 nm of the Stokes shift from Mn2+-doped Cd0.5Zn0.5S/ZnS core/shell quantum dots has been demonstrated and enhances ~0.5% of the PCE in Si solar cells. Since Mn2+-doped Cd0.5Zn0.5S/ZnS core/shell quantum dots basically performs a lower quantum yield (~51%) so that their PCE enhancement would be limited to less than 1%2. Thus, another challenge such as energy-up-conversion through the core/shell quantum dots is necessary to overcome the limit of EDS in enhancing the PCE of Si solar cells. In this presentation, we will discuss these issues. Reference 1. S.W.Baek, J.H.Shim, H.M.Seung, G.S.Lee, J.P.Hong, K.S.Lee, and J.G.Park, Nanoscale, 6, 12524 (2014). 2. M.Jalalah, Y.H.Ko, F.A.Harraz, M.S.Al-Assiri, and J.G.Park, Nano Energy, 33, 257 (2017)

Enhancement of GdVO 4 :Eu3+ red fluorescence through plasmonic effect of silver nanoprisms on Si solar cell surface

Abstract A comprehensive study on deposition and conjugation of red emitting phosphor (GdVO 4 :Eu 3+ ) and silver nanoprisms (Ag NP) on commercial single crystal silicon solar cell surface has been done to establish the optimum dielectric separating layer (PVA) sequence between consecutive species through confocal fluorescence mapping and spectroscopy. Results show that up to 310% fluorescence enhancement could be achieved in optimal arrangement of emitter, PVA and Ag NP layers on Si cell surface. The current work shows the potential of plasmon enhanced down shifting fluorescence of rare-earth doped vanadate in enhancing performance of SiPV devices.

Enhancement of Silicon Solar Cell’s Performance using Plasmonic Ag Nps

In this paper, Silver nanoparticles (Ag NPs) were prepared by laser ablation in liquid (PLAL) technique for different laser energy in water. Then the Ag NPs were deposited on the surface of Si solar cells to enhance their plasmonic absorption. The UV-VIS, FTIR spectrometer, and the Atomic force microscope were used to study the optical properties, composition, and the surface morphology of the NPs, respectively. The atomic absorption spectroscopy was also used to find the amount of ablated material. It is found that after the thermal deposition of the water drops containing Ag NPs on the surface of Silicon solar cells, the short circuit current and the overall conversion efficiency (η) have been improved. The short circuit current density (Jsc) has been increased by 14% after the drop overcasting of Ag NPs (about 92 nm in size) on the surface of silicon solar cells. The relative increase in Jsc may be attributed to the enhance plasmonic absorption for the incident light due to the forward scattering of Ag NPs.

Nanocatalytic Growth of Si Nanowires from Ni Silicate Coated SiC Nanoparticles on Si Solar Cell

We investigated the nanocatalytic growth of Si nanowires on the microtextured surface of crystalline Si solar cell. 3C-SiC nanoparticles have been used as the base for formation of Ni silicate layer in a catalytic reaction with the Si melt under H2 atmosphere at an annealing temperature of 1100 degrees C. The 10-nm thick Ni film was deposited after the SiC nanoparticles were coated on the microtextured surface of the Si solar cell by electron-beam evaporation. SiC nanoparticles form a eutectic alloy surface of Ni silicate and provide the base for Si supersaturation as well as the Ni-Si alloy layer on Si substrate surface. This bottom reaction mode for the solid-liquid-solid growth mechanism using a SiC nanoparticle base provides more stable growth of nanowires than the top reaction mode growth mechanism in the absence of SiC nanoparticles. Thermally excited Ni nanoparticle forms the eutectic alloy and provides collectively excited electrons at the alloy surface, which reduces the activation energy of the nanocatalytic reaction for formation of nanowires.

Improving Si solar cell performance using Mn:ZnSe quantum dot-doped PLMA thin film

Poly(lauryl methacrylate) (PLMA) thin film doped with Mn:ZnSe quantum dots (QDs) was spin-deposited on the front surface of Si solar cell for enhancing the solar cell efficiency via photoluminescence (PL) conversion. Significant solar cell efficiency enhancements (approximately 5% to 10%) under all-solar-spectrum (AM0) condition were observed after QD-doped PLMA coatings. Furthermore, the real contribution of the PL conversion was precisely assessed by investigating the photovoltaic responses of the QD-doped PLMA to monochromatic and AM0 light sources as functions of QD concentration, combined with reflectance and external quantum efficiency measurements. At a QD concentration of 1.6 mg/ml for example, among the efficiency enhancement of 5.96%, about 1.04% was due to the PL conversion, and the rest came from antireflection. Our work indicates that for the practical use of PL conversion in solar cell performance improvement, cautions are to be taken, as the achieved efficiency enhancement might not be wholly due to the PL conversion.

Heterogeneous Integration of InGaAs Nanowires on the Rear Surface of Si Solar Cells for Efficiency Enhancement

We demonstrate energy-conversion-efficiency (η) enhancement of silicon (Si) solar cells by the heterogeneous integration of an In(x)Ga(1-x)As nanowire (NW) array on the rear surface. The NWs are grown via a catalyst-free, self-assembled method on Si(111) substrates using metalorganic chemical vapor deposition (MOCVD). Heavily p-doped In(x)Ga(1-x)As (x ≈ 0.7) NW arrays are utilized as not only back-reflectors but also low bandgap rear-point-contacts of the Si solar cells. External quantum efficiency of the hybrid In(x)Ga(1-x)As NW-Si solar cell is increased over the entire solar response wavelength range; and η is enhanced by 36% in comparison to Si solar cells processed under the same condition without the NWs.

Limits to model amphoteric defect recombination via SRH statistics

AbstractIn semiconductor device modeling, it is common practice to approximate recombination via amphoteric defects by means of the Shockley–Read–Hall (SRH) theory. We show by means of a mathematically rigorous treatment that this approximation is only justified if: (i) the defect distribution of amphoteric defects is approximated by two equally‐shaped energy distributions of acceptor‐ and donor‐like defect states which are separated in energy by the effective correlation energy, (ii) the ratios of the capture cross‐sections (CCS) of free carriers for charged and neutral defect states are strongly asymmetric, (iii) the correlation energy is positive, and (iv) the defect density has its maximum between the quasi‐Fermi levels (QFLs) for the trapped carriers (TQFLs). In particular, we investigate this kind of SRH approximation for the case of injection‐dependent recombination at the interface between crystalline silicon (c‐Si) and amorphous silicon (a‐Si:H), a system that has recently been used to passivate the surface of Si solar cells. It is shown that care must be taken when applying this SRH approximation at low excess carrier densities Δn, e.g., at pn‐junctions between a‐Si:H and c‐Si or at low illumination levels, because the defect distributions may peak outside the TQFLs. We apply a self‐consistent model, which includes the band bending in c‐Si caused by both light‐induced, trapped charges in the a‐Si:H layer and at the a‐Si/c‐Si interface. We show that these trapped charges significantly influence the recombination rate and should be taken into account, as opposed to common practice.

Highly-ordered vertical Si nanowire/nanowall decorated solar cells

Highly-ordered vertical nanowire and nanowall arrays are studied on Si solar cell surface. The nanowall textured solar cell is found to be more effective in reducing the overall optical reflectance, resulting in higher short circuit current (Jsc = 24.9 mA/cm²) over nanowire structured (Jsc = 23.3 mA/cm²) and planar (Jsc = 17.5 mA/cm²) solar cells. The extracted energy conversion efficiency (η) from planar solar cell is 7.1%, while nanowire/nanowall cells show efficiency of 8.2% and 6.3%, respectively. If corrected with series resistance (Rs), nanowall solar cell exhibits the highest η of 9.8% in this experiment. A careful study of the series resistance from different types of the nanostructures is also presented.

Laser Textured Black Silicon Solar Cells with Improved Efficiencies

Femtosecond laser irradiation of silicon has been used for improving light absorption at its surface. In this work we demonstrate the successful implementation of femtosecond laser texturisation to enhance light absorption at Si solar cell surface. In order to adapt this technology into solar industry, the texturisation process is carried out in air ambient. The microstructure similar to what has been produced in vacuum can be made in air by using appropriate laser conditions. The texturised surface shows excellent optical properties with a reflectivity down to 7% without crystalline orientation dependence. Junction formation and metallisation proceeded after texturisation. Suns-Voc measurements are performed to evaluate the cell performance and decent electrical characteristics have been achieved.

Analysis of light trapping effects in Si solar cells with a textured surface by ray tracing simulation

The effects of the size and density of a pyramidal texture, as formed on the surface of Si solar cells to increase the light trapping efficiency, on the optical reflectance and absorptance were examined by comparing simulation results and experimental observations. A ray tracing algorithm capable of the direct calculation of the absorbed energy in active Si was utilized for the simulation. The simulation results showed that the optical reflectance spectra, i.e., the absorptances, of the textured surface with a fixed density of pyramids were not affected by the pyramid pitch, whereas the spectra with varying density of pyramids decreased with an increase in the density of the pyramids. Observations similar to the simulation results were observed from the experimentally textured surfaces, indicating that the density of the pyramid area, i.e., the area of the flat region, is the most crucial factor affecting the optical behavior of a textured Si surface with three-dimensional pyramid patterns.

Modeling and calculation of light absorption in silicon/metal nanocomposites

Silicon thin films over a glass substrate has been considerate an economical and viable alternative for the photovoltaic industry. Implementation of this technology will contribute to preserve a clean environment helping to reach a sustainable future. Nevertheless, by their own nature, Silicon thin films present small light absorption, and its electrical energy conversion mechanisms, besides their non ideal character, are not completely understood. The inclusions of metal nanoparticles in semiconductors can modify and improve the light absorption properties of these materials by surface plasmon interaction. It is well known that metal nanoparticles, deposited on the surface of Si-Solar cells, improve considerable the efficiency of the cell and it has been shown that there is a strong correlation between the surface plasmon excitation frequency and that of the exciting light. To study the light interactions on such material, we have developed a theoretical model that takes into account the incorporation of metallic nano-particles over Silicon thin films. We have obtained an analytical expression for the effective permittivity of the Semiconductor/Nano-particle system, ϵeff using this result we have analyzed the light absorption process in the case of Silicon with two types of metallic inclusions.

Characterization of surface recombination velocity at Si solar cell surface under high injection level

The illumination intensity dependence on the effective lifetimes of silicon wafers with SiO 2 passivation layers is measured. A chopped CW-YAG laser light of up to 877 mW/cm 2 is used to accurately measure the effective lifetimes. Also, the density of interface traps of the corresponding wafers is measured, and the SRH model is used to analyze the obtained dependence of surface recombination velocity on excess carrier concentration. The fitting analysis shows that the hole capture cross-section strongly depends on the conduction type and preparation conditions. In contrast, the electron capture cross-section remains the same, regardless of the conduction type or sample preparation conditions.