Laser applications in thin-film photovoltaics

We review laser applications in thin-film photovoltaics (thin-film Si, CdTe, and Cu(In,Ga)Se₂ solar cells). Lasers are applied in this growing field to manufacture modules, to monitor Si deposition processes, and to characterize opto-electrical properties of thin films. Unlike traditional panels based on crystalline silicon wafers, the individual cells of a thin-film photovoltaic module can be serially interconnected by laser scribing during fabrication. Laser scribing applications are described in detail, while other laser-based fabrication processes, such as laser-induced crystallization and pulsed laser deposition, are briefly reviewed. Lasers are also integrated into various diagnostic tools to analyze the composition of chemical vapors during deposition of Si thin films. Silane (SiH₄), silane radicals (SiH₃, SiH₂, SiH, Si), and Si nanoparticles have all been monitored inside chemical vapor deposition systems. Finally, we review various thin-film characterization methods, in which lasers are implemented.     

Polycrystalline silicon on glass for thin-film solar cells

Although most solar cell modules to date have been based on crystalline or polycrystalline wafers, these may be too material intensive and hence always too expensive to reach the very low costs required for large-scale impact of photovoltaics on the energy scene. Polycrystalline silicon on glass (CSG) solar cell technology was developed to address this difficulty as well as perceived fundamental difficulties with other thin-film technologies. The aim was to combine the advantages of standard silicon wafer-based technology, namely ruggedness, durability, good electronic properties and environmental soundness with the advantages of thin-films, specifically low material use, large monolithic construction and a desirable glass superstrate configuration. The challenge has been to match the different preferred processing temperatures of silicon and glass and to obtain strong solar absorption in notoriously weakly-absorbing silicon of only 1–2 micron thickness. A rugged, durable silicon thin-film technology has been developed with amongst the lowest manufacturing cost of these contenders and confirmed efficiency for small pilot line modules already in the 10–11% energy conversion efficiency range, on the path to 12–13%.     

新型高效太阳能电池研究进展

第三代太阳能电池以超高效率、薄膜化、低成本为主要目标,目前发展起来的有多结叠层太阳能电池、中间带太阳能电池、多激子产生太阳能电池、热载流子太阳能电池和热光伏太阳能电池等.文章简要介绍了以上几种新型太阳能电池的工作原理和最新进展,并对其发展前景作了分析和预测.     

Advanced solar materials for thin-film photovoltaic cells

As one of the most promising solutions for the green energy, thin-film photovoltaic cell technology is still immature and far from large-scale industrialization. The major issue is getting low cost and stable module efficiency. To solve these problems, a large amount of advanced solar materials have been developed to improve all parts of solar cell modules. Here, some new solar material developments applied in different critical parts of chalcogenide thin-film photovoltaic cells are reviewed. The main efforts are focused on improving light trapping and antireflection, internal quantum efficiency and collection of photo-generated carriers.     

High-Efficiency Silicon Solar Cells—Materials and Devices Physics

High-efficiency Si solar cells have attracted great attention from researchers, scientists, engineers of photovoltaic (PV) industry for the past few decades. Many researchers, scientists, and engineers in both academia and industry seek solutions to improve the cell efficiency and reduce the cost. This desire has drawn stronger support from major funding agencies and industry and stimulated a growing number of major research and research infrastructure programs, and a rapidly increasing number of publications in this filed. This article reviews materials, devices, and physics of high-efficiency Si solar cells developed over the last 20 years and presents representative examples of superior performances and competitive advantages. In this paper there is a fair number of topics, not only from the material viewpoint, introducing various materials that are required for high-efficiency Si solar cells, such as base materials (FZ-Si, CZ-Si, MCZ-Si, and multi-Si), emitter materials (diffused emitter and deposited emitter), passivation materials (Al-BSF, high-low junction, SiO₂, SiO_x, SiN_x, Al₂O₃ and a-Si:H), and other functional materials (antireflective layer, transparent conductive oxide and metal electrode), but also from the device and physics point of view, elaborating on physics, cell concept, development, and status of most types of high-efficiency Si solar cells, including passivated emitter and rear contact (PERC), passivated emitter and rear locally diffused (PERL), passivated emitter and rear totally-diffused (PERT), Pluto, PANDA, interdigitated back-contacted (IBC), emitter-wrap-through (EWT), metallization-wrap-through (MWT), heterojunction with intrinsic thin-layer (HIT), and so on. Finally, the technical data of these high-efficiency Si solar cells has been tabulated.     

Organic photovoltaic materials and devices

Organic photovoltaic solar cells bere an important potential of development in the search for low-cost modules for the production of domestic electricity. We review the principles and techniques needed for their development: organic semiconductors, their transport properties and photophysical characteristics, photovoltaic molecule and polymer structures, device technologies, electrical and optical behaviour of the cells, state of the art, limitations and perspectives. Despite some recent record efficiencies, research on organic solar cells is still in its infancy when stability and efficiency have to be compared with the performances of silicon cells. A nominal 10% solar efficiency is the research target for the next few years. To cite this article: J.-M. Nunzi, C. R. Physique 3 (2002) 523–542.     

Si-Ge-GaAs nanoheterostructures for photovoltaic cells

Synthesis from molecular beams in an ultrahigh vacuum is a promising method for producing multilayer semiconducting thin-film structures for high-efficiency conversion of heat and solar energies into electricity, where cascade converters with complex optimized chemical compositions and alloying profiles are necessary. Until recently, nanotechnologies of heterostructures, such as quantum wells, superlattices, and quantum dots, were not applied for photovoltaic conversion. The state of the art of technologies in this field is analyzed.     

Characterization of a low concentrator photovoltaics module

Low concentration photovoltaic (LCPV) systems have the potential to reduce the cost per kWh of electricity compared to conventional flat-plate photovoltaics (PV) by up to 50%. The cost-savings are realised by replacing expensive PV cells with relatively cheaper optical components to concentrate incident solar irradiance onto a receiver and by tracking the sun along either 1 axis or 2 axes. A LCPV module consists of three interrelated subsystems, viz., the optical, electrical and the thermal subsystems, which must be considered for optimal module design and performance. Successful integration of these subsystems requires the balancing of cost, performance and reliability. In this study LCPV experimental prototype modules were designed, built and evaluated with respect to optimisation of the three subsystems and overall performance. This paper reports on the optical and electrical evaluation of a prototype LCPV module.     

Multifunctional Sulfur-Hyperdoped Silicon Nanoparticles with Engineered Mid-Infrared Sulfur-Impurity and Free-Carrier Absorption

Si nanoparticles (NPs), which are innovative promising light-harvesting components of thin-film solar cells and key-enabling biocompatible theranostic elements of infrared-laser and radiofrequency hyperthermia-based therapies of cancer cells in tumors and metastases, are significantly advanced in their near/mid-infrared band-to-band and free-carrier absorption via donor sulfur-hyperdoping during high-throughput facile femtosecond-laser ablative production in liquid carbon disulfide. High-resolution transmission electron microscopy and Raman microscopy reveal their mixed nanocrystalline/amorphous structure, enabling the extraordinary sulfur content of a few atomic percents and very minor surface oxidation/carbonization characterized by energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. A 200-nm thick layer of the nanoparticles exhibits near−mid-infrared absorbance, comparable to that of the initial 380-micron thick n-doped Si wafer (phosphor-dopant concentration ≈10¹⁵ cm⁻³), with the corresponding extinction coefficient for the hyperdoped NPs being 4–7 orders higher over the broadband spectral range of 1–25 micrometers. Such ultimate, but potentially tunable mid-IR structured, multi-band absorption of various sulfur-impurity clusters and smooth free-carrier absorption are break through advances in mid-infrared (mid-IR) laser and radiofrequency (RF) hyperthermia-based therapies, as envisioned in the RF-heating tests, and in fabrication of higher-efficiency thin-film and bulk photovoltaic devices with ultra-broad (UV−mid-IR) spectral response.     

PbS量子点在荧光集光太阳能光伏器件上的应用

荧光集光太阳能光伏器件在平面光波导效应的作用下实现等效聚光,可以减少太阳能电池的用量,有效降低光伏发电的成本。将胶体化学法制备的吸收和发射在近红外波段的单分散球状PbS量子点荧光材料封装于两片光伏超白玻璃间的正己烷溶液中,构成溶液夹层封装的平面光波导,并和效率为17%的单晶硅太阳能电池耦合,制作出了吸收在700～1000nm,效率约为1.31%的近红外荧光集光太阳能光伏器件。     

Crystalline Si thin-film solar cells: a review

The present review summarizes the results of research efforts in the field of crystalline silicon thin-film solar cells on foreign substrates. The large number of competing approaches can be broadly classified according to the grain size of the crystalline Si films and the doping of the crystalline absorber. Currently, solar cells based on microcrystalline Si films on glass with an intrinsic or moderately doped absorber film achieve efficiencies around 10%, whereas thin-film cells fabricated from large-grained polycrystalline Si on high-temperature-resistant substrates have efficiencies in the range of 15%. The paper discusses the limitations of various approaches and describes recent developments in the area of thin, monocrystalline Si films that may open the way towards 20% efficient thin-film Si solar cells. Received: 1 March 1999 / Accepted: 28 March 1999 / Published online: 24 June 1999     

Research status in thin-film crystalline Si solar cells

Recent research status and future subjects for the development of thin-film crystalline Si solar cells were reviewed. Optimum design of cell configuration and polycrystalline silicon growth by atmospheric pressure chemical vapor deposition (APCVD) were demonstrated. In order to configure high efficiency thin-film poly-Si solar cells, a novel method of quasi-three-dimensional simulation using a cylindrical coordinate system was carried out. Interface recombination velocity at grain boundaries should be less than 10³ cm/s based on the simulation results. Even at a relatively short diffusion length of L_n=50 μm, high efficiency larger than 16% will be expected at a thickness of 5–20 μm. Poly-Si films with columnar structures whose diameter was around 5 μm were successfully deposited on foreign substrates with APCVD at a high growth rate of 0.8 μm/min. Up-to-date status of reported cell performances were discussed in addition to future prospects.     

硅薄膜太阳能电池研究的进展

从制备方法、材料和结构的观点出发,概述非晶硅（a-Si)和多晶硅（poly-Si)薄膜太阳能电池研究的进展。对非晶硅特别是对多晶硅薄膜太阳能电池研究的重要结果进行了讨论。阐述非晶硅太阳能电池的各种应用,并对其光电系统进行介绍。对太阳能电池新产品如太阳能电池屋顶瓦及超轻灵活的太阳能电池的开发也作了简介。对由太阳能电池提供动力的空调设备作了叙述。讨论所得出的创新方案。     

Silicone oxidation for a‐Si:H passivation of wafers bonded to glass

A possible scenario for wafer‐based silicon photovoltaics is the processing of solar modules starting from thin silicon wafers bonded to glass. However, interactions between the adhesive used for bonding and the solar cell processing can affect the surface passivation of the bonded wafer and decrease cell performances. A method that suppresses these interactions and leads to state‐of‐the‐art a‐Si:H surface passivation is presented in this Letter. The method is based on an increase of the surface cross‐linking of a silicone adhesive by means of an O₂ plasma and it is successfully tested on three different silicones. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

铁电体的光伏效应

介绍了铁电光伏效应的发展历史和现状,通过与传统半导体p-n结光伏器件比较,旨在阐述铁电光伏器件非比寻常的优点和重要的应用前景.铁电光伏效应分为体光伏效应和反常光伏效应,多种物理机制已被发现,无疑为铁电光伏效应的提高指明了方向.还对钙钛矿氧化物、卤化物和双钙钛矿结构氧化物等铁电体中的光伏效应进行了阐述,讨论了通过引入新的自由度实现多功能性光伏器件的可能性.     

N-type amorphous silicon-based bilayers for cost-effective thin-film silicon photovoltaic devices

We investigate the improvement of p–i–n type thin-film silicon (Si) solar cells by employing a hydrogenated n-type amorphous Si (n-a-Si:H)-based bilayer. The initial conversion efficiency (η) of a-Si:H single-junction solar cells is improved from 9.2 to 10.0%. The developed n-a-Si:H-based bilayer is also suitable for a-Si:H/hydgrogenated microcrystalline Si (μc-Si:H) double-junction solar cells, and thus initial η is improved from 10.4 to 10.8%. With a further optimization, initial η of 11.3% and stabilized η of 10.1% are achieved. Since the n-a-Si:H-based bilayer is easily formed using a conventional process, it can be a promising option for cost-effective mass production of large-area thin-film Si solar modules.     

Amorphous thin-film solar cells

This report gives an overview of the present status of thin-film solar cells made from hydrogenated amorphous semiconductors (a-Si:H, a-Ge:H) together with new results emphasizing the physics of amorphous materials and devices. Preparation techniques, quality and performances of a-Si:H and a-Ge:H films as well as solar cells with pin structures are reviewed. Dark and light current-voltage I(V) characteristics and spectral response measurements give information about photovoltaic diodes and allow further insights into the physics of these kinds of materials and solar cells. Simulation calculations and device modelling of such solar cells have increased our understanding of amorphous semiconductors and their devices. The introduction of pin/pin stacked and/or tandem structures has improved the long-term stability and conversion efficiency of amorphous solar cells.Dedicated to H.-J. Queisser on the occasion of his 60th birthday     

Light Harvesting and Enhanced Performance of Si Quantum Dot/Si Nanowire Heterojunction Solar Cells

Si nanowires (Si NWs) structures with good antireflection and enhanced optical‐absorption properties are used to fabricate Si quantum dots/Si NWs heterojunction solar cells. The Si NWs prepared by the metal‐assisted chemical‐etching technique exhibit a very low reflection in a wide spectral range (300–1200 nm). Correspondingly, the optical absorption reaches as high as 88.9% by weighting AM1.5G solar spectrum. Both the short current density and open current voltage are improved compared to the reference flat cell. However, the photovoltaic properties are degraded by varying the Si NWs with long etching time, possibly due to the increased etching‐induced surface states. The optimal Si NWs lead to the best cell with the power conversion efficiency of 11.3%.     

Thermal conductivity and interface thermal resistance of Si film on Si substrate determined by photothermal displacement interferometry

An in situ, noncontact, photothermal displacement interferometer for performing thermal diffusivity measurements on bulk and thin-film materials has been developed. Localized transient surface motion is generated through photothermoelastic coupling of a pulsed, heating laser beam to the sample under investigation. The maximum surface displacement is found to be linearly dependent on the laser power while the proportionality is a function of the thermal diffusivity. Both thin-film conductivity and film/substrate interface thermal resistance are derived from the measured, effective thermal conductivity by employing simple heat-flow analysis. Wedge-shaped Si films, vacuum deposited on single crystal Si wafers are studied with this technique. A sample with oxide layer removed by ion bombardment of the wafer surface prior to film deposition shows the same film conductivity as a sample film deposited on an as-cast wafer, while the uncleaned sample exhibits higher interface thermal resistance. It is found that the thin-film thermal conductivity is somewhat smaller than the bulk value. However, the existence of an interface thermal resistance, when combined with film thermal conductivity, can result in an effective thermal conductivity as low as two orders of magnitude lower than the bulk value.Currently supported by the LLE fellowship     

对硅薄膜型太阳电池的一些思考

在当前迅速发展的绿色环保能源中,硅太阳电池一直占据着首要地位.然而晶体硅太阳电池(单晶硅和多晶硅)由于价格昂贵和材料短缺已不能满足绿色能源快速发展的需要.因此,薄膜型太阳电池已经被视为今后发展的主要方向.非晶硅薄膜太阳电池虽然在性能上还具有不少缺点,但随着薄膜沉积技术的改进以及膜本身质量的不断提高,它在太阳电池领域中仍占有一席之地.多晶硅薄膜太阳电池集晶体硅与非晶硅电池的优点为一体,也受到人们的关注.然而,后起之秀纳米硅薄膜太阳电池,依靠其本身的优越性以及当前纳米技术的进展,将会成为一个新的亮点.