Annual available radiation for fixed and tracking collectors

Single crystal silicon solar cells are potential elements of large scale solar energy conversion systems. Current costs of these cells are too high at least in part because current production methods require single crystal wafers obtained by slicing cylindrical single crystal ingots. This paper reviews a U.S. research program aimed at reducing the cost of silicon cells by developing new methods of growing silicon ribbons and sheets from which high efficiency solar cells can be fabricated. The paper also describes novel techniques for lower cost processes for ingot growth and wafer slicing which are included in this research and development program.     

Characteristics of structural defects in the 240 kg silicon ingot grown by directional solidification process

Multi-crystalline silicon for solar cell over single crystalline silicon is its capability of using cheaper raw material. Since cheaper material contains harmful metal impurities, gettering technology has to be applied to silicon wafers to reduce the metal content in the crystal. Low dislocation density in the 240 kg multi-crystalline silicon crystal provides the strong possibility of gettering for the low cost silicon solar cell. Saw damage induced during the slicing process of multi-crystalline silicon ingot was confirmed to generate dislocation loops which can be employed for extrinsic gettering.     

Recovery of minority carrier lifetime in low-cost multicrystalline silicon

Lifetime of minority carriers has been widely identified to be the key material parameter determining the conversion efficiency of pn-junction silicon solar cells. Impurities and defects in the silicon crystal lattice reduce the charge carrier lifetime and thus limit the performance of the solar cells. Removal of impurities by silicon material purification is often contradictory with low cost production of photovoltaic devices. In this paper, we present experimental results of an efficient gettering technique which can be applied to low cost processing of multicrystalline silicon solar cells without any additional process steps or compromises with optimal device design parameters. This technique is based on well-known phosphorous gettering. We have discovered that if the silicon wafers are kept in the furnace after the emitter diffusion at the 700°C, significant improvement in the lifetime will take place. At this temperature the properties of the pn-junction remain unaffected meanwhile many lifetime killers are still mobile. The time needed for this temperature program can be easily modified in order to respond to the material quality variations in substrates originating from different parts of multicrystalline ingot. Better control of lifetime can lead to higher degree of starting material utilization.     

Photovoltaic materials, past, present, future

This paper traces briefly the history of this photovoltaic materials and it tries to look at possible future scenarios. A large part of the paper is concerned with silicon although from solid-state physics we know that silicon is not the ideal material for photovoltaic conversion. From the first solar cell developed at Bell Laboratories in 1954 photovoltaics was dominated by silicon. The reasons for this dominating position are investigated. Crystalline silicon today has a market share of 86% which is almost equally distributed between single crystal and cast silicon. Amorphous silicon has another 13%. The main endeavor is to reduce cost. Present trends in the crystalline field are reviewed. The conventional technology still has significant potential for cost reduction but this comes only with increasing volume. A problem to be solved is the supply of solar-grade silicon material. Other future possibilities include thin film crystalline silicon on different substrates. Because of the low absorption coefficient of silicon light trapping is required. True thin film materials need only 1–2 μm of material. Amorphous silicon, copper indium diselenide (CIS) and CdTe are hopeful approaches for very cost-effective solar cells. Some other, more speculative materials and concepts are described at the end of this paper     

硅珠的形成及太阳电池（组件）

将Ｓｉ３Ｎ４与Ｓｉ粒混合，在单晶炉或快速热退火炉中分别集装熔化法或平铺熔化法，制备太阳电池用硅珠，试验了不同工艺条件对硅珠品质的影响，并制作了硅珠太阳电池（组件）。     

Mono- and tri-crystalline Si for PV application

Crystalline silicon wafers are by far the dominant absorber materials for today's production of solar cells and modules due to their good price/performance relation and their proven environmental stability. These wafers are mainly produced either by a solar-optimized Czochralski (Cz)-growth method yielding crystalline silicon with low defect density (c-Si) or by a directional solidification or a ribbon growth method yielding large grained multi-crystalline (mc-Si) wafers with higher defect density. To further improve the price/performance relation of Cz solar cells, tri-crystalline silicon (tri-Si) is being developed as a high-quality wafer material that combines both the high diffusion length of minority carriers of up to 1300 μm of c-Si and the productivity of mc-Si. More than 1000 μm LID free diffusion length could be reached with specially doped tri-crystals. Due to an increased mechanical stability tri-Si allows both quasi-continuous pulling and thin slicing with higher mechanical yields. This paper reviews the structural, electronic, and mechanical properties of tri-crystalline silicon wafers with respect to c-Si wafers for solar applications. Actual non-textured solar cells processed with a simple cost effective fabrication process exhibit the same cell efficiencies up to 15.9% for both tri-silicon and mono-silicon wafers. With an improved process, up to 18% cell efficiency can be obtained with textured mono-Si.     

A review of thin-film crystalline silicon for solar cell applications. Part 2: Foreign substrates

One of the most promising ways to reduce the cost of photovoltaics is thin-film crystalline silicon solar cells. This paper, together with part 1, reviews the current state of research in thin-film crystalline silicon solar cells. Deposition on silicon, novel techniques which use a high-quality, reusable silicon substrate and light trapping have been described in part 1 of this paper. This paper describes deposition on glass and ceramics and discusses cell designs for thin-film crystalline silicon solar cells.     

Overview of solar cell technologies and results on high efficiency multicrystalline silicon substrates

Fabrication technologies for multicrystalline silicon (mc-Si) solar cells have advanced in recent years with efficiencies of mc-Si cells exceeding 18%. Intense efforts have been made at laboratory level to improve process technology, growth methods, and material improvement techniques to deliver better devices at lower cost. Deeper understanding of the physics and optics of the device led to improved device design. This provided a fruitful feedback to the industrial sector. Both screenprinting and buried-contact technologies yield cells of high performance. An increasingly large amount of research activity is also focussed on the fabrication of thin solar cells on cheap substrates such as glass, ceramic, or low quality silicon. Success of these efforts is expected to lead to high efficiency devices at much lower costs. Efforts are also being put on low thermal budget processing of solar cells based on rapid thermal annealing.     

颗粒硅带多晶硅薄膜太阳电池的研制

以工业硅粉为原料制备出颗粒硅带（SSP），对颗粒硅带表面形态进行了分析。以SSP为衬底，采用快速热化学气相沉积（RTCVD）法生长多晶硅薄膜，并以此制作出效率为2．93％的颗粒硅带多晶硅薄膜太阳电池，这在国内属首先。并报道了对以SSP为衬底的多晶硅薄膜太阳电池的初步研究结果，同时讨论了该类电源的结构、工艺特点和改进措施。     

Thin crystalline silicon solar cell bonded to sintered substrate with aluminum paste

Making thinner wafers is a simple way to reduce the production cost of silicon solar cells. However, thin wafers need to be supported mechanically in order to avoid the problem of breakage. Among the several possible supporting materials, silicon substrate made from the sintering of silicon powder, which is produced during the slicing process is the most favorable one because of its abundance and its similar thermal expansion coefficient with silicon wafers. For the bonding of the substrate and thin silicon wafers, aluminum paste is selected because of its compatibility with silicon and the possible BSF effect. Silicon solar cells of 150 μm with the sintered substrate on the back show 5.42% in solar cell conversion efficiency. Compared to commercial silicon cells, lower J_sc is obtained. This might be due to the poor conduction in the back layer of aluminum, which is absorbed into the supporting substrate during the annealing process.     

Testing of materials for solar power space applications

This paper summarizes the results of a program initiated at the Naval Research Laboratory to test conventional and state-of-the-art solar power space systems by flying them aboard satellites. The program (approximately nine years in duration) confirmed the practicality of improvements in advanced silicon solar cells such as textured surfaces, shallow junctions, back surface field and back surface reflector techniques, as well as novel methods of bonding coverslips to conventional cells. In addition, the performance of gallium aluminum arsenide solar cells first tested in a space environment and demonstrated to be satisfactory. Finally, advanced silicon cells such as lithium-diffused and vertical junction cells, which were reported to be radiation resistant on the basis of measurements in the laboratory, were found unsuitable for extended space application.     

Status and research development of Si NWs/PEDOT∶PSS hybrid solar cells

硅基太阳电池作为当前主流的光伏器件,进一步降低成本并提升效率仍是人们努力的方向.基于此,一方面,可以从太阳电池材料入手,用硅纳米线阵列代替平板硅,硅纳米线阵列具有优异的光学和电学性能,可大幅减少光反射,增加光的吸收和利用,有望提高光伏器件的效率,并可降低硅原料消耗,降低材料成本;另一方面,将硅微纳结构与有机材料进行复合,充分利用两种材料的优势,制备杂化太阳电池,以达到增强稳定性,提高效率和降低成本的目的.本文概括了Si纳米线阵列SiNWs/PEDOT∶PSS杂化太阳电池的发展现状和存在的问题,并针对相应问题的解决思路和发展方向进行了讨论.     

A review of thin-film crystalline silicon for solar cell applications. Part 1: Native substrates

Approximately half the cost of a finished crystalline silicon solar module is due to the silicon itself. Combining this fact with a high-efficiency potential makes thin-film crystalline silicon solar cells a growing research area. This paper, written in two parts, aims to outline world-wide research on this topic. The subject has been divided into techniques which use native substrates and techniques which use foreign substrates. Light trapping, vapour- and liquid-phase deposition techniques, cell fabrication and some general considerations are also discussed with reference to thin-film cells.     

Identification of some key parameters limiting the performance of high-efficiency silicon solar cells

Several theoretical calculations and barriers to achieving high-efficiency silicon solar cells have been discussed in the past. Cell efficiencies between 44% and 17% have been estimated assuming different spectra of illumination and sets of cell parameters. Plausible reasons for such a large variation in the cell efficiency have also been discussed.This paper presents, for the first time, a detailed sensitivity analysis of key cell parameters on cell efficiency by incorporating advanced solar cell physics in a sophisticated numerical simulation program. It delineates the true physical barriers to obtaining a high-efficiency silicon solar cell. Specific parameters presently limiting cell efficiency are identified to be the minority carrier lifetime and the recombination velocities at the front and back surfaces. Practical cell efficiencies in the vicinity of 22% are estimated to be attainable by using good quality silicon crystal and substantially reducing surface recombination velocities.     

硅太阳电池稳步走向薄膜化

考察了硅太阳电池在光伏产业中所处的地位,分析了薄膜硅太阳电池的发展趋势。指出硅太阳电池在未来15a仍将保持优势地位,并继续沿着晶硅电池和薄膜硅电池两个方向发展。在此发展过程中,两个发展方向的主流很可能会汇合到一起,共同促使低成本、高效率、高可靠薄膜晶硅电池的诞生和产业化,从而继续保持硅太阳电池的优势地位。     

Modifying the solar spectrum to enhance silicon solar cell efficiency—An overview of available materials

There are three ways in which the cell efficiency of silicon solar cells may be improved by better exploitation of the solar spectrum: down-conversion (cutting one high energy photon into two low energy photons), photoluminescence (shifting photons into wavelength regions better accepted by the solar cell) and up-conversion (combining low energy photons to one high energy photon). In this paper, we present the state of the art of these three methods and discuss the suitability of materials available today for application to silicon solar cells.     

Present status and future of crystalline silicon solar cells in Japan

Crystalline silicon solar cells show promise for further improvement of cell efficiency and cost reduction by developing process technologies for large-area, thin and high-efficiency cells and manufacturing technologies for cells and modules with high yield and high productivity.In this paper, Japanese activities on crystalline Si wafers and solar cells are presented. Based on our research results from crystalline Si materials and solar cells, key issues for further development of crystalline Si materials and solar cells will be discussed together with recent progress in the field. According to the Japanese PV2030 road map, by the year 2030 we will have to realize efficiencies of 22% for module and 25% for cell technologies into industrial mass production, to reduce the wafer thickness to 50–100 μm, and to reduce electricity cost from 50 Japanese Yen/kWh to 7 Yen/kWh in order to increase the market size by another 100–1000 times.     

Reduction of optical losses in colored solar cells with multilayer antireflection coatings

Solar modules are becoming an everyday presence in several countries. So far, the installation of such modules has been performed without esthetic concerns, typical locations being rooftops or solar power plants. Building-integrated photovoltaic (BIPV) systems represent an interesting, alternative approach for increasing the available area for electricity production and potentially for further reducing the cost of solar electricity. In BIPV, the visual impression of a solar module becomes important, including its color. The color of a solar module is determined by the color of the cells in the module, which is given by the antireflection coating (ARC). The ARC is a thin film structure that significantly increases the amount of current produced by and, hence, the efficiency of a solar cell. The deposition of silicon nitride single layer ARCs with a dark blue color is the most common process in the industry today and plasma enhanced chemical vapor deposition (PECVD) is mostly used for this purpose. However, access to efficient, but differently colored solar cells are important for the further development of BIPV. In this paper, the impact of varying the color of an ARC upon the optical characteristics and efficiency of a solar cell is investigated. The overall transmittance and reflectance of a set of differently colored single layer ARCs are compared with multilayered silicon nitride ARCs, all made using PECVD. These are again compared with porous silicon ARCs fabricated using an electrochemical process allowing for the rapid and simple manufacture of ARC structures with many tens of layers. In addition to a comparison of the optical characteristics of such solar cells, the effect of using colored ARCs on solar cell efficiency is quantified using the solar cell modeling tool PC1D. This work shows that the use of multilayer ARC structures can allow solar cells with a range of different colors throughout the visual spectrum to retain very high efficiencies.     

离心铸造太阳电池硅片液态成形机制的研究

为了将离心铸造技术成功地移植到低成本超薄多晶太阳电池硅片的成形工艺上，提出了ＥＬＣＣ技术的硅片液态成形方法，即将铸模型腔预热至硅熔点以上温度，过热的硅液被浇注到型腔后，在离心力的作用下始终保持液态充型。这种成形机制易于实现厚度小于１ｍｍ的硅片的完整成形，而且对模具转速、硅液过热度等要求较低。采用该方法，硅片的成形与结晶不会同时发生，可以在硅片液态成形后，采用定向凝固的方法获得粗大的定向柱晶组织，提高硅片的光伏性能。采用理论分析、计算机模拟与工艺实验相结合的方法，对ＥＬＣＣ技术硅片液态成形机制进行了研究，为进一步对硅片凝固过程组织控制的研究奠定基础。     

非晶硅太阳能光伏/光热空气集热器性能对比实验研究

文章设计了新型非晶硅太阳能PV/T空气集热器,该空气集热器能够解决传统太阳能PV/T热水器在高温波动情况下,晶硅电池热应力大的问题,同时避免了冬季管道发生霜冻的现象。文章通过实验对比,分析了非晶硅太阳能PV/T空气集热器、单独非晶硅光伏电池和传统太阳能空气集热器的能量效率和[火用]效率的差异。分析结果表明:非晶硅太阳能PV/T空气集热器的平均热效率为45.70%,比传统太阳能空气集热器的平均热效率降低了约25.88%;当空气质量流量增大至0.048 kg/s时,非晶硅太阳能PV/T空气集热器中的非晶硅光伏电池的平均电效率高于单独非晶硅光伏电池,它们的平均电效率分别为4.70%,4.54%;非晶硅太阳能PV/T空气集热器的总[火用]效率高于传统太阳能空气集热器的热[火用]效率和单独非晶硅光伏电池的电[火用]效率,非晶硅太阳能PV/T空气集热器总[火用]效率最大值为7.14%。文章的分析结果为非晶硅太阳能PV/T空气集热器的推广提供了参考。