Milestones in the development of crystalline silicon solar cells

The development of crystalline silicon solar cells is traced from their invention to the present day, with an emphasis on the major advances (“milestones”) along the way. The survey covers cells for power generation in space as well as those for terrestrial applications.     

Passivation and gettering of defective crystalline silicon solar cell

Different polycrystalline silicon and single-crystalline silicon with dislocations were used for passivation and gettering processes. These materials have defects and more impurity in the crystal. The dominant increase of electronic performance was found for wafers with more defects by using a different casting method. The wafers of single crystalline silicon with dislocations also have higher increase of efficiency of cell in comparison with that wafer without dislocations during oxide passivation processes used. POCl₃ was used for gettering processes. Single-crystal wafer with or without dislocations was used for comparison of gettering.     

Angle-dependent XPS analysis of silicon nitride film deposited on screen-printed crystalline silicon solar cell

In this work silicon nitride (Si₃N₄) film was deposited as an antireflection coating (ARC) on crystalline silicon solar cell (cell?A) using plasma-enhanced chemical vapor deposition (PECVD). Two solar cells XA and XB of approximately equal area were diced from cell#A and characterized by angle-dependent X-ray photoelectron spectroscopy (XPS). The XPS profiling shows the presence of silicon (Si), nitrogen (N), carbon (C) and oxygen (O) in the Si₃N₄ film. The presence of C and O indicates that organic substances, involved in processing steps were not released completely from the surface and may diffuse in Si₃N₄ ARC during deposition. The XPS spectra corresponding to Si2p, N1s, C1s and O1s were recorded at angles 0° (normal to the surface), 30° and 45°, as angle increases spectra becomes more surface sensitive. Peak positions in Si2p and N1s spectra explain the oxygen contamination in the Si₃N₄ film. The shift in the peak positions of C1s and O1s as angle increases from 0° to 45° explains the surface contamination of carbon and oxygen. The atomic composition of elements Si, N, C and O show more carbon, oxygen concentration and smaller N/Si ratio than stoichiometry, i.e. Si₃N₄ in cell XB. However, cell XA not only show better photovoltaic performance in terms of parameters open-circuit voltage (V_oc), short-circuit current density (J_sc), fill factor (FF) and efficiency (η) but also have more uniform texturization and regular pyramids on the surface as revealed by scanning electron microscopy (SEM). The presence of higher concentration of impurities (carbon and oxygen), non-uniformity in texturization and in the Si₃N₄ film as well could be responsible for less satisfactory photovoltaic performance of cell XB.     

Effect of the front surface field on crystalline silicon solar cell efficiency

The present paper reports on a simulation study carried out to determine and optimize the effect of the high–low junction emitter (n⁺-n) on thin silicon solar cell performance. The optimum conditions for the thickness and doping level of the front surface layer with a Gaussian profile were optimized using analytical solutions for a one dimensional model that takes on the theory relevant for highly doped regions into account. The photovoltaic parameters of silicon solar cells with front surface field layer (n⁺-n-p structure) and those of the conventional one (n-p structure) are compared. The results indicate that the most important role played by the front surface field layer is to enhance the collection of light-generated free carriers, which improves the efficiency of the short wavelength quantum. This is achieved by a drastic reduction in the effective recombination at the emitter upper boundary, a property primarily responsible for the decrease in the emitter dark current density. The findings also indicate that the solar cell maximum efficiency increase by about 2.38% when the surface doping level of the n⁺-region and its thickness are equal to 2.10²⁰ cm^?3 and 0.07 μm, respectively.     

The design and optimization of advanced multijunction solar cells using the Silvaco ATLAS software package

In this paper, the design and optimization of advanced multijunction photovoltaic devices, utilizing a newly introduced modeling technique (J. Sol. Energy Mater. Sol. Cells, submitted for publication), is demonstrated. In our opinion, the introduction of this modeling technique to the photovoltaic community will prove to be of great importance in aiding the design and optimization of advanced solar cells. A model of an InGaP/GaAs/InGaNAs/Ge four-junction solar cell is prepared and is fully simulated. The major stages of the process are explained and the simulation results are compared to published theoretical and experimental data. An example of cell parameters optimization is also presented. The flexibility of the proposed methodology is demonstrated. The methodology and design considerations for this process are explained.     

我国太阳电池研究和产业现状分析

我国从1958年开始光伏电池的研究,1976年开始生产硅太阳电池,至今已有40多年的历史。本文利用重庆维普资讯有限公司http://vip.whu.edu.cn/vip/的“中文科技期刊全文数据库”及中国学术期刊网http://www.nj.cnki.net/的“中文期刊全文数据库”,结合2002年1O月在杭州市召开的“中国第七届光伏会议”的情况。对我国1992年至2002年10年间在太阳电池研究方面的资料进行了分析统计,介绍我国光伏电池研究及产业的发展现状。     

Six Sigma-based approach to optimise the diffusion process of crystalline silicon solar cell manufacturing

Silicon-based photovoltaics (PV) plays the dominant role in the history of PV due to the continuous process and technology improvement in silicon solar cells and its manufacturing flow. In general, silicon solar cell process uses either p-type- or n-type-doped silicon as the starting material. Currently, most of the PV industries use p-type, boron-doped silicon wafer as the starting material. In this work too, the boron-doped wafers were considered as the starting material to create pn junction and phosphorus was used as n-type doping material. Industries use either phosphorous oxy chloride (POCl₃) or ortho phosphoric acid (H₃PO₄) as the precursor for doping phosphorous. While the industries use POCl₃ as the precursor, the throughput is lesser than that of the industries’ use of H₃PO₄ due to the manufacturing limitations of the POCl₃-based equipments. Hence, in order to achieve the operational excellence in POCl₃-based equipments, business strategies such as the Six Sigma methodology have to be adapted. This paper describes the application of Six Sigma Define–Measure–Analyze–Improve–Control methodology for throughput improvement of the phosphorus doping process. The optimised recipe has been implemented in the production and it is running successfully. As a result of this project, an effective gain of 0.9 MW was reported per annum.     

All electrochemical layer deposition for crystalline silicon solar cell manufacturing: Experiments and interpretation

A manufacturing process for crystalline silicon solar cells is presented which consists mainly of electrochemical steps. The deposition of doping glass layers for the front side emitter as well as the back surface field is performed anodically onto the etched and cleaned wafers. The doping atoms, phosphorus or boron, are diffused into the silicon crystal in a furnace at 950 °C in an atmosphere of simply clean air. After the diffusion process the front side doping glass has a blue colour and is suitable to serve as an antireflection coating with a very low surface recombination velocity. For this reason, the doping glass is not etched away on the sun exposed regions of the solar cell. The masking technology for all electrochemical processes provides inherently an edge exclusion and, therefore, no additional processing for preventing shorts on the wafer edge is necessary. For the metallization a reusable rubber mask defines the pattern. First, the mask is used for the doping glass patterning by wet chemical etching. Then, on both sides first nickel is deposited electrolytically directly onto silicon, and in a second step copper electroplating onto the nickel barrier is performed. All three steps, etching, nickel and copper deposition are self adjusting through said rubber mask. A short forming gas anneal finishes the solar cell processing. During all electrochemical processing the wafer is electrically contacted on the opposite surface on a stainless steel plate by the force of vacuum clamping. With this low cost processing 12.5% cell efficiency has been achieved on multi-crystalline 156 mm wafers, which originally have a minority carrier lifetime of 4 μs measured after damage etch and thermal oxidation. In this paper, experiments, surface analysis and physical interpretations are presented.     

太阳能烟囱发电站模型的分析与研究

介绍了太阳能烟囱发电站的工作原理，并在给定参数下对太阳能烟囱的主要设计参数进行了计算，得到了太阳能烟囱内气流速度的最大值。通过数值计算对太阳能烟囱内的速度场进行了模拟，并与计算结果进行了比较，讨论了影响太阳能电站发电功率的主要因素，分析了将太阳能烟囱建设在山坡上的可行性。     

Optimization of fabrication process of high-efficiency and low-cost crystalline silicon solar cell for industrial applications

The process conditions for a high-efficiency and low cost crystalline silicon solar cell were optimized. Novel approaches such as wafer cleaning and saw -damage removal using 0.5 wt% of 2,4,6-trichloro-1,3,5-triazine, silicon surface texturing with optimized pyramid heights (∼5 μm), and a third step of drive-in after phosphosilicate glass (PSG) removal followed by oxide removal were investigated. A simple method of chemical etching adopted for edge isolation was optimized with edge etching of 5-10 μm, without any penetration of chemicals between the stacked wafers. The conversion efficiency, open-circuit voltage, short-circuit current, and fill factor of the cell fabricated with the optimized process were a maximum of 17.12%, 618.4 mV, 5.32 A, and 77% under AM1.5 conditions, respectively.     

Solar cell research and development in Australia

Australia's demography and geography conspire to make it a relatively large user of solar cells on a purely commercial basis.Telecommunications has dominated these commercial applications. Due to the expectation of low grid electricity costs into the foreseeable future, the focus of research and developmental efforts has been remote area applications. The main areas of activity have been silicon solar cell research, cell and module testing, and the development of remote area power supplies for applications in the “outback”.     

The effects of temperature and light concentration on the GaInP/GaAs multijunction solar cell’s performance

Monolithic Ga_0.49In_0.51P/GaAs cascade solar cells with a p⁺/n⁺ GaAs tunnel junction were grown by MOCVD technique. The variation of the photovoltage, photocurrent, fill factor, efficiency, I–V characteristics and spectral response under different temperatures (25–75 °C), and light intensity values (1–40 sun), were investigated experimentally.The open-circuit voltage of the multijunction cell decreases with the temperature increase at a rate of 5.5 mV/°C. The efficiency of the cascade structure under investigation was increased with an increase in the light concentration up to a point where the series resistance and the tunnel junction effects become significant.     

Silicon solar cell materials research: current progress and future needs

This paper presents a brief review of the research being carried out under the crystalline silicon materials research program. The primary emphasis of this program is the development of processes for post-growth quality enhancement of low-cost silicon substrates. The various electronic mechanisms that can be exploited for material quality enhancement are summarized. Major research results of the current program and some important aspects of future research are identified.     

Energy-efficiency research, development and demonstration : New roles for US states

At least eight states have established energy research, development and demonstration (RD&D) programmes. In contrast to federal and utility energy RD&D, most states emphasize applied research on end-use efficiency and renewable energy. States also try to closely link research and technology deployment, in some cases deliberately blurring the line between the two. The states discussed in this paper spend about US$39 million per year for energy RD&D, or one-fifth of the US Department of Energy (DOE) budget for conservation and renewable energy RD&D. When indexed per capita or per energy dollar, the average rate of state RD&D spending on conservation and renewables is about 65–75% that of the US DOE.     

Improving thin-film crystalline silicon solar cell efficiency with back surface field layer and blaze diffractive grating

Both 2D electromagnetic and electrical semiconductor simulations are performed sequentially in this study in order to better understand the structural principles of thin-film crystalline solar cells with back surface field and blaze diffractive grating. In the absence of adequate approximations for blazed gratings, we simulate silicon solar cells electromagnetically and electrically in order to deal with the geometrical complexity produced by the blazed grating with a BSF on top of it. Thin-film crystalline silicon solar cells (TF-c-Si SCs) typically exhibit poor quantum efficiency both at shorter wavelengths and longer wavelengths with sharp drops in spectral response. Longer wavelength spectral response (from 0.6 μm to 1.2 μm) is addressed here first by considering the influence of blaze gratings on the enhancement of effective optical absorption in thin-film crystalline silicon (TF-c-Si) solar cells. The effect of the back surface field layer (BSF) in terms of improving minority carrier collection is also taken into account. In the 2D electromagnetic simulation, polarization dependent two-dimensional (2D) numerical simulations based on rigorous coupled wave analysis (RCWA) and finite element method (FEM) are implemented for the optimization of optical absorption of the solar cell structure. A rather large tolerance in design parameters of the optimized blaze grating structure was found. The optimized blaze grating structures help in improving the cell efficiency, especially for weak absorption thin cell structures. The enhancement of equivalent optical path length reveals the efficient light trapping effect caused by the diffractions of the blaze grating structures, especially in the longer wavelength range. In the electrical semiconductor simulation, the BSF, which arises from the heavy acceptor doping that creates the concentration gradient, is set atop the blaze grating in order to provide an extra small drift field for the collection of minority electrons. Incorporating the optimized antireflection coating along with a BSF layer and a blaze-grating in the 2 μm cell doubles cell efficiency. The use of blazed gratings in thin-film solar cells, which can be performed upon silicon by means of lithography and ion-beam etching, is promising for low cost and high-efficient solar cell applications.     

Si-film growth using liquid phase epitaxy method and its application to thin-film crystalline Si solar cell

We have developed a new apparatus for the growth of liquid-phase epitaxy (LPE)-Si films on 5 in Si wafers. We have obtained high growth rates of 0.1–1.0 μm/min and minority-carrier lifetime of average value of 10 μs over the whole of wafer, whereas the thickness uniformity was degraded when rotating the wafers in the solvent. We also demonstrated to growth of LPE-Si films on porous Si layers and to separate the Si films from the porous layers. A 9.5% cell was obtained using a LPE-Si film after separation.     

Fuel cell research and development projects in Austria

A five year program on energy storage and fuel cell research has been established in Austria, with the goal to find out what types of batteries and fuel cells could possibly be optimized for commercial applications. In the background there are environmental considerations and others, leading to a future hydrogen economy, also possibly to a use in electric vehicles. The search of the European Space Agency for a suitable system for the HERMES manned space vehicle is contributing considerably to the future prospects. The work in Austria is mainly oriented to low temperature alkaline fuel cell systems and the studies are complementary to a similarly oriented program in Canada, originally started by the Institute for Hydrogen Systems in Mississauga, subsequently continued by private companies in cooperation with the University of Toronto.     

A review of research and development work on solar dryers with heat storage

Drying of agricultural food products is one of the most attractive and cost-effective applications of solar energy. The solar dryer is less reliable due to the intermittent nature of solar energy. This shortcoming can be overcome to some extent by storing solar energy. Information on sensible and latent heat storage materials and systems is spread widely in the literature. In this paper, we try to gather information about the previous and current research works in the field of thermal energy storage technology for solar air heater and dryer. The relative studies are classified on the basis of the type of storage material used in solar dryers, i.e. phase change material (PCM), rock, water, etc. Several designs of solar dryers with different heat storage materials were proposed by researchers. Recent studies focused on PCMs such as Paraffin and salt hydrate, due to their high heat storage capacity per unit volume.     

Solar cell research and development using the hot wire CVD process

This article reviews the research and development of solar cells fabricated using the hot wire CVD (HWCVD) process. A short history of the technique is given, and the advantages of this deposition technique as they relate to solar cell fabrication are quantified. A chronological history of solar cell fabrication involving three major research groups, with a long history in HWCVD solar cell fabrication, is then given, as such histories illustrate the evolution of solar cell research involving HWCVD. Illustrative examples of activities of new research groups entering this field are then discussed, and the outlook for this field is given.