Silicon Solar Cell Applications Research Articles

Contact resistivity decrease at a metal/semiconductor interface by a solid-to-liquid phase transitional metallo-organic silver.

We present a new approach to ensure the low contact resistivity of a silver paste at a metal/semiconductor interface over a broad range of peak firing temperatures by using a solid-to-liquid phase transitional metallo-organic silver, that is, silver neodecanoate. Silver nanoclusters, thermally derived from silver neodecanoate, are readily dissolved into the melt of metal oxide glass frit even at low temperatures, at which point the molten metal oxide glass frit lacks the dissociation capability of bulk silver into Ag(+) ions. In the presence of O(2-) ions in the melt of metal oxide glass frit, the redox reaction from Ag(+) to Ag(0) augments the noble-metal-assisted etching capability to remove the passivation layer of silicon nitride. Moreover, during the cooling stage, the nucleated silver atoms enrich the content of silver nanocolloids in the solidified metal oxide glass layer. The resulting contact resistivity of silver paste with silver neodecanoate at the metal/semiconductor interface thus remains low-between 4.12 and 16.08 mΩ cm(2)-whereas without silver neodecanoate, the paste exhibits a contact resistivity between 2.61 and 72.38 mΩ cm(2) in the range of peak firing temperatures from 750 to 810 °C. The advantage of using silver neodecanoate in silver paste becomes evident in that contact resistivity remains low over the broad range of peak firing temperatures, thus providing greater flexibility with respect to the firing temperature required in silicon solar cell applications.

Silicon and Energy

Since man discovered fire there has been an ongoing interest in energy. However, as a consequence of the Industrial Revolution, energy, water and food are the most valuable resources for human life and therefore energy is central for technology innovation. Since the turn of the 18th century, there remain tremendous challenges in order to provide sustainable and environmentally responsible energy and material resources for advancing and developing society as a whole. Silicon-based materials, in particular, play a vital role in enabling technologies that can offer promising solutions to achieve renewable and sustainable energy pathways for the future. Herein, we highlight selected articles that are on the forefront to addressing the limited availability, high-cost, and new potential for Si-based materials for emerging energy technologies. These articles include descriptions of the processing of silicon for solar cell applications and batteries which are based on new small molecule silicon systems.

Effective optimization of indium tin oxide films by a statistical approach for shallow emitter based crystalline silicon solar cell applications

In this study, we propose a statistical approach based on Taguchi method and Grey relational analysis for effective optimization of indium tin oxide (ITO) films which are used as front contact for shallow emitter based crystalline silicon (c-Si) solar cells. The experiments were designed by the Taguchi method through an orthogonal array, resulting in the reduction of the number of experiments by approximately 90%; the reproduction effect of process parameters on performance characteristics, however, is still ensured. Excellent compromise between electrical and optical properties of ITO films was obtained by Grey relational analysis at power density of 0.685W/cm2, working pressure of 0.4Pa, substrate temperature of 250°C, and post-annealing temperature of 300°C in 30min. The ITO films exhibited lowest electrical resistivity of 1.316×10−4Ωcm, and highest transmittance of 91.251% under optimal condition. The shallow emitter based c-Si solar cells using the optimal ITO films showed highest efficiency of 17.555%, yielding a 1.375% absolute increase in efficiency compared to using ITO films with initial condition. Furthermore, using analysis of variance, we found that the substrate temperature was a key parameter which critically affected the opto-electrical properties of ITO films.

Enhancement of the light trapping by double-layered surface texture of ITO/AZO and AZO/AZO transparent conductive films

Double-layered surface textures of ITO/AZO (In2O3:Sn/ZnO:Al) and AZO/AZO transparent conductive films are conducted with a process of deposition, first-etching, re-deposition and re-etching. Light trapping ability can be greatly reinforced by the induced double broad feature distributions. For the re-etching process, stronger etching pits with 400–600nm feature sizes and ~68nm Root Mean Square (RMS) roughness are obtained in AZO/AZO films compared to that of the first-etching samples. The use of Fe(III) catalyst can greatly increase the etching rate. Diffuse transmittance with the largest value (56.97%) is observed for the double-layered AZO–HCl/AZO–HCl+FeCl3 sample due to the formation of crater-like morphology in the mezzanine and the surface of the films. The double-textured AZO samples exhibit higher haze values (50.73% and 55.50%) at 550nm, corresponding to the AZO/AZO samples using HCl+FeCl3 or HCl alternately. For ITO related samples, the resistivity keeps the order of 10−4Ωcm after the re-deposition. While, for AZO/AZO films, a slight increment of resistivity and carrier concentration is observed due to the chemical etching. These double-textured structures imply that the films have potential application in thin film silicon (TFS) solar cells for light trapping.

Hybrid silver nanoparticle and transparent conductive oxide structure for silicon solar cell applications

AbstractTransparent conductive oxides (TCOs) have been widely used as electrodes for various solar cell structures. For heterojunction silicon wafer solar cells, the front TCO layer not only serves as a top electrode (by enhancing the lateral conductance of the underlying amorphous silicon film), but also as an antireflection coating. These requirements make it difficult to simultaneously achieve excellent conductance and transparency, and thus, only high‐quality indium tin oxide (ITO) has as yet found its way into industrial heterojunction silicon wafer solar cells. In this Letter, we present a cost‐effective hybrid structure consisting of a TCO layer and a silver nano‐particle mesh. This structure enables the separate optimization of the electrical and optical requirements. The silver nanoparticle mesh provides high electrical conductance, while the TCO material is optimized as an antireflection coating. Therefore, this structure allows the use of cost‐effective (and less conductive) TCO materials, such as aluminium‐doped zinc oxide. The performance of the hybrid structure is demonstrated to achieve a similar visible transmission (∼86% in the 380–780 nm range) as an 80 nm thick ITO layer, but with 10 times better lateral conductance. The presented hybrid structure thus seems well suited for a variety of photovoltaic devices. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A Study of Back Electrode Stacked With Low Cost Reflective Layers For High-Efficiency Thin-Film Silicon Solar Cell

In this study, commercially available white paint is used as a pigmented dielectric reflector (PDR) in the fabrication of a low-cost back electrode stack with an Al-doped ZnO (AZO) layer for thin-film silicon solar cell applications. An initial AZO film was deposited by the radio-frequency magnetron sputtering method. In order to obtain the highest transmittance and lowest resistivity of AZO film, process parameters such as sputtering power and substrate temperature were investigated. The optimal 100-nm-thick AZO film with low resistivity and high transmittance in the visible region are 6.4 × 10−3 Ω·cm and above 80%, respectively. Using glue-like white paint doped withTiO2 nanoparticles as the PDR enhances the external quantum efficiency (EQE) of a microcrystalline silicon absorptive layer owing to the doped white particles improving Fabry–Pérot interference (FPI), which raises reflectance and scattering ability. To realize the cost down requirement, decreasing the noble metal film thickness such as a 30-nm-thick silver reflector film, and a small doping particle diameter (D50 = 135 nm) and a high solid content (20%) lead to FPI improvement and a great EQE, which is attributed to improved scattering and reflectivity because of optimum diameter (Dopt) and thicker PDR film. The results indicate that white paint can be used as a reflector coating in low-cost back-electrode structures in high-performance electronics.

Design of two dimensional silicon nanowire arrays for antireflection and light trapping in silicon solar cells

Silicon nitride coated nanowire arrays have been investigated as an efficient antireflection structure for silicon solar cells. The minimum average reflectance could reach 1.62% under AM1.5 spectrum. Scattering effects of silicon nanowire arrays also result in enhanced absorption in the substrate, and analytical results show that the scattered light can be well trapped in silicon substrate when the back surface is passivated by silicon dioxide. This ultra-low surface reflection property combined with light trapping effect may have potential applications in silicon solar cells with thin substrate.

ポーラスシリコンを用いる太陽電池

ポーラスシリコンを用いる太陽電池

Luminescence of hydrothermally fabricated PbF 2 :Er 3+ particles and their application in bifacial silicon solar cells

We report the synthesis of PbF 2 :Er 3+ particles using a hydrothermal method. The structure and upconversion emission properties of the products are investigated by scanning electron microscopy, X-ray diffractometer, Raman spectrophotometer and fluorescence spectrometry. An increase in Er 3+ concentration in the crystals changes the PbF 2 structure from a mixed phase to a cubic phase and decreases the grain size to nanoscale levels. Enhanced upconversion efficiency is achieved after annealing resulted from the formation of the cubic phase and the increase of grain size. The optimal Er 3+ concentration is found to be 4% after annealing, and applied to the back of a bifacial silicon solar cell, maximum external quantum efficiencies of 0.38% and 0.79% are respectively obtained under 0.77 W/cm 2 laser excitation (1560 nm) and AM1.5 + laser co-excitation.

MOCVD ZnO/Screen Printed Ag Back Reflector for Flexible Thin Film Silicon Solar Cell Application

We have prepared Ag back electrode by screen printing technique and developed MOCVD ZnO/screen printed Ag back reflector for flexible thin film silicon solar cell application. A discontinuity and poor contact interface between the MOCVD ZnO and screen printed Ag layers caused poor open circuit voltage (Voc) and low fill factor (FF); however, an insertion of a thin sputtered ZnO layer at the interface could solve this problem. The n type hydrogenated amorphous silicon (a-Si:H) film is preferable for the deposition on the surface of MOCVD ZnO film rather than the microcrystalline film due to its less sensitivity to textured surface, and this allowed an improvement in the FF. The n-i-p flexible amorphous silicon solar cell using the MOCVD ZnO/screen printed Ag back reflector showed an initial efficiency of 6.2% withVoc=0.86 V,Jsc=12.4 mA/cm2, and FF = 0.58 (1 cm2). The identical quantum efficiency and comparable performance to the cells using conventional sputtered Ag back electrode have verified the potential of the MOCVD ZnO/screen printed Ag back reflector and possible opportunity to use the screen printed Ag thick film for flexible thin film silicon solar cells.

Magnetostriction‐strain‐induced enhancement and modulation of photovoltaic performance in Si‐p–n/TbxDy1−xFe2 composite

High photovoltaic efficiency is a key index in the application of silicon (Si) solar cells. In this study, a composite of a photovoltaic Si p–n junction solar cell and a magnetostrictive TbxDy1−xFe2 alloy was fabricated. By utilizing the magnetostrictive strain to modulate the energy bandgap of Si, the open‐circuit voltage and the maximum photovoltaic output power of the Si p–n junction solar cell could be enhanced by ∼12% and 9.1% under a dc magnetic field of ∼250 mT, respectively. The significantly enhanced photovoltaic performance and the simple fabrication process make the Si‐p–n/TbxDy1−xFe2 composite a promising material for high‐efficiency solar cell devices. The structure of the proposed Si‐p–n/TbxDy1−xFe2 laminated composite.

Development of Screen-Printed Texture-Barrier Paste for Single-Side Texturization of Interdigitated Back-Contact Silicon Solar Cell Applications.

Continuous cost reduction of silicon-based solar cells is needed to lower the process time and increase efficiency. To achieve lower costs, screen-printed texture-barrier (SPTB) paste was first developed for single-side texturization (ST) of the interdigitated back-contact (IBC) for silicon-based solar cell applications. The SPTB paste was screen-printed on silicon substrates. The SPTB paste was synthesized from intermixed silicate glass (75 wt %), a resin binder (ethyl cellulose ethoce: 20 wt %), and a dispersing agent (fatty acid: 5 wt %). The silicate glass is a necessity for contact formation during firing. A resin binder and a dispersing agent determine the rheology of the SPTB paste. In this work, by modulating various parameters, including post SPTB firing, alkali texturing, and removal of the SPTB, the ST of IBC silicon solar cells was achieved. Since the advantages of the SPTB paste include low toxicity and prompt formation of the texture-barrier, SPTB is potentially suited for simple fabrication at low-cost for solar cell applications. The cost of the SPTB is around $100/kg which is lower than the SiH4/NH3 gas ambient used in plasma-enhanced chemical vapor deposition (PECVD). Thus, the expensive Si3N4 film deposited by PECVD using SiH4 and NH3 gas ambient for silicon solar cells can be replaced by this SPTB.

An image processing approach to approximating interface textures of microcrystalline silicon layers grown on existing aluminum-doped zinc oxide textures

We present an algorithm for generating a surface approximation of microcrystalline silicon (μc-Si) layers after plasma enhanced chemical vapor deposition (PECVD) onto surface textured substrates, where data of the textured substrate surface are available as input. We utilize mathematical image processing tools and combine them with an ellipsoid generator approach. The presented algorithm has been tuned for use in thin-film silicon solar cell applications, where textured surfaces are used to improve light trapping. We demonstrate the feasibility of this method by means of optical simulations of generated surface textures, comparing them to simulations of measured atomic force microscopy (AFM) scan data of both Aluminum-doped zinc oxide (AZO, a transparent and conductive material) and μc-Si layers.

Preparation of Self-Assembled Au Nanoparticles Arrays for Silicon Solar Cell Applications

Au nanoparticles arrays for silicon solar cells were fabricated by self-assembly method to accommodate manufacturing process of traditional silicon solar cells. Surface morphologies of 10-30 nm thick films after annealing treatment at 600 °C and 700 °C were analyzed. It indicated that morphological features of Au nanoparticles arrays such as particle shapes, size distribution vary with thicknesses of Au films, annealing temperatures and surface morphologies of substrates.

Fabrication and antireflection properties of solar cells with pyramid–nanohole texture by caesium chloride lithography

Pyramids and nanoholes are integrated together to form a micro–nano-texture on silicon surface in order to suppress reflection for silicon solar cell application. The nanoholes are formed by inductively coupled plasma (ICP) dry etching employing a nanoporous aluminum (Al) mask which is fabricated by caesium chloride (CsCl) nanoislands lift-off technique. Reflection of less than 4% can be reached by pyramid–nanohole texture, which is much lower than that from pure pyramids or nanoholes texture. Higher short circuit current density (Jsc) and photovoltaic conversion efficiency (PCE) are obtained for the solar cell with pyramid–nanohole texture due to its better antireflection. The average diameter and depth of the nanoholes affect the solar cell properties. The smaller and deeper nanoholes can suppress reflection a lot, but meanwhile, the formation of them means more crystal lattice defects generated from ICP etching. An optimized diameter of 800 nm and depth of 1 µm for the nanoholes are obtained in our experiments to get the best photovoltaic performance that is a PCE of 14.89% with a Jsc of 38.25 mA cm−2 and an open circuit voltage (Voc) of 544.8 mV.

Optimization of an i-a-SiOx:H absorber layer for thin film silicon solar cell applications

Wide gap, high quality hydrogenated intrinsic amorphous silicon (i-a-Si:H) alloy films are essentially required for multi-junction solar cells fabrication to enhance the open-circuit voltage (Voc) of the top cell. In this paper, intrinsic hydrogenated amorphous silicon oxide films (i-a-SiOx:H) have been prepared using a very high frequency plasma-enhanced chemical vapor deposition technique for use as an absorber layer of the top cell for double-junction amorphous silicon thin film solar cells. We studied the effects of the carbon dioxide (CO2) to silane (SiH4) ratio on the properties of the i-a-SiOx:H films and also optimized these films for application in a-SiOx:H/a-Si:H double-junction solar cells. The Voc of the a-SiOx:H/a-Si:H double-junction solar cells was higher than that of conventional a-Si:H/a-Si:H double-junction solar cells. Using an optimized deposition condition, a-SiOx:H/a-Si:H double-junction solar cell with an initial cell efficiency (η) of 10.2% was produced.

Optical transparency of ZnO thin film using localized surface plasmons of Ag nanoislands

Localized surface plasmons mediated optical transparencies of ZnO/Ag/ZnO, ZnO/Ag and Ag/ZnO have been investigated. These multilayered films have been fabricated using a combination of simple techniques like Spray Pyrolysis and Vacuum Deposition. A clear signature of localized surface plasmons has been observed in transmission spectra due to silver nanoislands. This is in contrast to other previously reported articles, which use mainly sputtering method. Key factor for this difference is the fabrication technique. Salient feature of these multilayer films is also the extremely high transmittance (near 95%) in the range 600–900nm with transmission minima in the range 450–550nm. Experimental results are successfully interpreted theoretically using extended Maxwell–Garnett (EMG) effective medium theory and transfer matrix method. These observed results may have potential applications in high efficiency silicon solar cells.

Random reactive ion etching texturing techniques for application of multicrystalline silicon solar cells

To maximize the conversion efficiency of solar cells by improving the trapping of incident light, surface texturing of multicrystalline silicon wafers is a more permanent and effective solution to decrease reflections compared with antireflection coatings. In general, many techniques of wet chemical surface texturing depend on crystal orientation. Also, these processes place a limitation on the growth of solar production capacity due to consumption of the large amount of material, de-ionized water and chemicals. Reactive ion etching (RIE) is therefore useful for mc-Si solar cells with the random grain orientation. In this study, we have fabricated mc-Si solar cells with a large-area (156mm×156mm) by a random RIE texturing method using SF6/O2 plasma chemistry. A large amount of silicon loss, which is due to saw damage removal and texturing process of mc-Si wafers, have dramatically decreased by applying RIE texturing process. As a result of the optimum RIE process, the best mc-Si solar cell showed conversion efficiency, fill factor, short circuit current density, and open circuit voltages as high as 17.4%, 80%, 35mA/cm2 and 620mV, respectively. This study demonstrates that it is possible to apply the thin mc-Si Solar cells fabrication for low cost and high efficiency in conventional industrial production line.

Modeling the front side plasmonics effect in nanotextured silicon surface for thin film solar cells application

We report the computational modeling of the front side plasmonics effect arising on gold (Au) nanoparticles array in combination with nanotextured silicon surface for thin film silicon solar cells application. The ultimate efficiency of the optimized silicon nanoholes (SiNH) array textured surface using Au plasmonics effect is 38.58 %, which is 24.01 % greater than SiNH array textured surface without Au plasmonics effect. Furthermore, SiNH array textured surface perform better compared to silicon nanopillar (SiNP) array textured surface for all the parameters studied. The maximum possible short circuit current density and power conversion efficiency of the proposed SiNH array textured surface with Au plasmonics effect are 31.57 mA/cm2 and 25.45 % respectively, which compares favorably well to the computed values of 26.17 mA/cm2 and 21.12 %, respectively for the SiNP array textured surface with Au plasmonics effect.

Optical characterisation of a spectrally tunable plasmonic reflector for application in thin-film silicon solar cells

We have investigated the interaction between a random two-dimensional array of Ag islands near a Ag reflector, with the aim of producing a plasmonic back reflector structure with high diffuse reflectivity in the near-infrared, 600–1100nm wavelength, region. We have demonstrated the ability to tune the power scattered and absorbed by varying the distance between the plasmonic layer and the reflector. Finite-difference-time-domain (FDTD) simulations demonstrate the tunability of the scattered and absorbed power with separation distance for a single Ag nanosphere near a planar Ag reflector. The tunability of the optical properties can be attributed to the modulation in the electric field driving the plasmonic resonance with separation distance. The simulation results indicate an intermediate distance where the scattered power peaks with minimal absorption losses. Random arrays of metal-islands were fabricated on varying thicknesses of a ZnO separation layer on a Ag reflector. Compared to a conventional textured Ag reflector, which has ∼2% diffuse reflectance in the near-infrared spectral region, the fabricated plasmonic reflector with ∼200nm sized Ag metal islands at 100nm separation distance from the Ag reflector shows a relatively higher, ∼24%, integrated diffuse reflectance in the near bandgap, 600–1100nm wavelength, region for thin film silicon solar cells.