Combined power of perovskites and silicon solar cells

The photovoltaic (PV) or solar cells technology can be categorised into two main groups, the wafer‐based and thin‐film based PVs. The wafer‐based PVs include the commonly known crystalline silicon (c‐Si) and gallium arsenide (GaAs) cells. The GaAs cells exhibit higher efficiency compared to crystalline silicon (c‐Si) cells but it is the later that dominates the commercial market. Thin‐film based (2nd Generation) PVs, including cadmium telluride (CdTe), amorphous silicon (a‐Si:H) and copper‐indium‐gallium‐selenide (CIGS), generally absorb light more efficiently than wafer‐based cells and can allow the use of materials in very thin films form. CdTe PVs have proven to be highly efficient but holds only a few percentage share of the market. There is still a need for more R&D before further commercialisation. An emerging and relatively new class of thin‐film based photovoltaics (3rd Generation) technology that has the potential to overcome the current energy conversion efficiencies and performance by making use of novel materials. This class of PVs include organic photovoltaic (OPV), dye‐synthesised solar cells (DSSC), quantum‐dot (QD) and last but not least, the perovskite PV. Perovskite PVs can offer a low cost energy generation solution with the best device conversion efficiencies have shot from lower than 4% in 2009 to more than 21% in 2016. Perovskite based devices can be fabricated using vacuum thermal evaporation or by solution processing of the active layers. Although most recent perovskite solar cells with record efficiencies (>20%) are prepared via solution processing, the early breakthrough in perovskite solar cells was made with vacuum processed perovskites thin films. Vacuum thermal evaporation offers the ability and flexibility to prepare solar cell devices in various configuration. Recent developments in the field of perovskite demonstrates its compatibility with both, first and second generation PV technologies, and is therefore likely to be embraced by the conventional PV industry and make its way into utility‐scale power generation.     

Surface and Interface Properties in Thin‐Film Solar Cells: Using Soft X‐rays and Electrons to Unravel the Electronic and Chemical Structure

Thin‐film solar cells have great potential to overtake the currently dominant silicon‐based solar cell technologies in a strongly growing market. Such thin‐film devices consist of a multilayer structure, for which charge‐carrier transport across interfaces plays a crucial role in minimizing the associated recombination losses and achieving high solar conversion efficiencies. Further development can strongly profit from a high‐level characterization that gives a local, electronic, and chemical picture of the interface properties, which allows for an insight‐driven optimization. Herein, the authors' recent progress of applying a “toolbox” of high‐level laboratory‐ and synchrotron‐based electron and soft X‐ray spectroscopies to characterize the chemical and electronic properties of such applied interfaces is provided. With this toolbox in hand, the activities are paired with those of experts in thin‐film solar cell preparation at the cutting edge of current developments to obtain a deeper understanding of the recent improvements in the field, e.g., by studying the influence of so‐called “post‐deposition treatments”, as well as characterizing the properties of interfaces with alternative buffer layer materials that give superior efficiencies on large, module‐sized areas.     

Hochdurchsatzbeschichtungen für die Photovoltaik

High throughput coatings for photovoltaics – Contribution of sputtering technology to Paris Climate Goals Photovoltaics (PV) is one of the most important renewable energy sources whose expansion is needed to achieve the climate goals. The considerable drop down in the costs of PV based energy within the last 10 years has led to a very high degree of economic attractiveness for photovoltaics. This was made possible by new cell structures with higher efficiencies, lower material usage and utilization of scaling effects as well as automation in production. Highly efficient PVD coating processes, such as the magnetron sputtering, are increasingly being used in current crystalline PV cell types such as heterojunction or TOPCON solar cells. Thin film technologies are still the backbone for processing of the less material‐intensive thin‐film solar modules.     

Crystalline Silicon Thin‐Film Solar Cells on Silicon Nitride Ceramic Substrates

Photovoltaics—the generation of electricity from sunlight—is a technically challenging but environmentally benign technology to generate electricity with a large economical potential. However, the major hurdle for its widespread usage is its present high cost. Various thin‐film solar cell technologies are investigated to bring down the total cost to an economic value. One of them, the crystalline silicon thin‐film (CSiTF) solar cell combines the advantages of conventional wafer‐based silicon solar cells such as high efficiency and non‐toxicity with the benefits of thin‐film technologies such as serial interconnection and large area deposition. This paper reports for the first time the preparation of CSiTF solar cells on specially developed Si₃N₄ ceramic substrates. Three different types of Si₃N₄ ceramic wafers were single‐sided coated with 10μm of microcrystalline silicon, which was recrystallized by a zone melting step and subsequently thickened to approx. 30 μm. Optical analysis of the layer surface and cross sections was done to determine the crystallographic properties of the silicon layers, as well as mass spectroscopy to measure the concentration of transition metal impurities. A one‐side contacted solar cell process was applied on non‐conducting Si₃N₄ substrates. The best 1 cm² cells achieved an efficiency of 8.0 % with an excellent fill factor of 74 % and an open circuit voltage of 554 mV. The solar cell characterization was complemented by measurements of dark current–voltage characteristics, spectrally resolved light beam induced current mapping, and external quantum efficiency.     

Anlagen für die Solarzellen‐Schichterzeugung benötigen hervorragend ausgelegte Vakuumsysteme

Vacuum pumps are an enabling technology for solar power because all modules require vacuum processing at various stages of production. Specially engineered products that are helping to make solar modules more affordable by reducing equipment downtime and improving process performance are essential to become a successful partner for the solar industry. The processes used for thin film technology are extremely demanding. Pump performance for high flows of light gases must be achieved and in parallel safety aspects must be considered carefully. The pump solutions must be extreme reliable in order to guarantee maximum tool up‐time which is mandatory for a production line in order to be cost competitive. Design and performance of such solutions must be qualified in close collaboration between pump supplier and the equipment producer together wi^th the user of the equipment. Experience and know how from industries using similar processes like semiconductor, large area coating or FPD production can be applied for solar production lines which can help to reduce time to market. The article will outline the specific needs for thin film solar cells based on amorphous silicon and CdTe.     

薄膜太阳能电池的进展和展望

薄膜太阳能电池因具有价格低、弱光性好、大面积自动化生产、柔性便携等优点,表现出极大的发展意义和良好的市场前景。目前光伏市场上薄膜太阳能电池主要分为硅基薄膜太阳能电池、碲化镉薄膜太阳能电池、铜铟镓硒薄膜太阳能电池三大类。本文介绍了三种薄膜太阳能电池的发展现状,指出了它们的优点和存在的主要问题,分析了学术界和产业界针对这些问题的解决方案,展望了其发展前景。     

制备硅薄膜太阳能电池的先进技术与实验研究

介绍了Si薄膜太阳能电池的材料与结构,重点介绍了几种叠层薄膜太阳能电池,详细阐述了近年发展的用于制备低成本、高效率Si薄膜太阳能电池的技术与最新的实验研究成果,其中高温沉积法、低温沉积法、层转移法尤为重要,展望了Si薄膜太阳能电池未来的技术发展和科研方向.三叠层薄膜太阳能电池是有发展前景的产品之一,更多叠层的薄膜太阳能电池与量子点叠层薄膜太阳能电池将长期作为实验研究的热门课题.     

Reaktives Magnetronsputtern von Dünnschichtsolarzellen

Reactive Magnetron Sputtering of Thin Film Solar Cells We show that reactive magnetron sputtering is well suited to deposit CuInS₂‐thin film absorber layers of high electronic quality. Using metallic targets and substrate temperatures below 500 °C, compact films with grain sizes in the micrometer range can be obtained. The structural and electronic properties of these layers are comparable to CuInS₂ thin films prepared by a 2‐step sulfurization process, which is being commercialized at present. In particular, the reactively sputtered films show minority carrier diffusion lengths larger than the layer thickness (≈ 2μm). This results in solar cells with conversion efficiences larger than 10 %, comparable to the best conversion efficiencies for CuInS₂‐solar cells obtained from other deposition processes. These results are promising for the potential application of magnetron sputtering as a large area deposition process for absorber layers in thin film solar cells.     

CdTe thin film technology: Leading thin film PV into the future

CdTe is a near perfect material for PV application with a direct band gap of ～1.5 eV that is closely matched to the terrestrial solar spectrum and a high optical absorption coefficient where less than 1 μm thickness is adequate to absorb the incident light. CdTe thin film solar cell and module technology has validated the economies of scale that were projected for thin film PV technologies since the early 1980s where manufacturing costs are now below $0.84 with module efficiencies of 11.1%. Additionally, the low-temperature coefficient of CdTe modules results in a high annualized output. A critical issue for CdTe manufacturers is that there is not a clear pathway to increase the module performance to 15% or beyond based on current laboratory results and efficiency improvements will require fundamental improvements in the CdTe semiconductor properties and/or developing an alternative device structure.     

Solution Processing of Chalcogenide Semiconductors via Dimensional Reduction

The quest to develop thin‐film solution processing approaches that offer low‐cost and preferably low‐temperature deposition, while simultaneously providing quality semiconductor characteristics, has become an important thrust within the materials community. While inorganic compounds offer the potential for outstanding electronic properties relative to organic systems, the very nature of these materials rendering them good electronic materials—namely strong covalent bonding—also leads to poor solubility. This review presents a “dimensional reduction” approach to improving the solubility of metal chalcogenide semiconductors, which generally involves breaking the extended framework up into discrete metal chalcogenide anions separated by small and volatile cationic species. The resulting soluble precursor may be solution‐processed into thin‐film form and thermally decomposed to yield the desired semiconductor. Several applications of this principle to the solution deposition of high‐performance active layers for transistors (channel mobility >10 cm² V⁻¹ s⁻¹), solar cells (power conversion efficiency of as high as 12%), and fundamental materials study will be presented using hydrazine as the deposition solvent.     

Thin-film solar cells

The rapid progress that is being made with inorganic thin-film photovoltaic (PV) technologies, both in the laboratory and in industry, is reviewed. While amorphous silicon based PV modules have been around for more than 20 years, recent industrial developments include the first polycrystalline silicon thin-film solar cells on glass and the first tandem solar cells based on stacks of amorphous and microcrystalline silicon films (“micromorph cells”). Significant thin-film PV production levels are also being set up for cadmium telluride and copper indium diselenide.     

Plasmatechnik in der Photovoltaikindustrie

Application of Plasmatechnology in Photovoltaic Industry Ever since the introduction of attractive feed‐in tariffs for photovoltaic electricity generation, there has been a huge surge in all kinds of photovoltaic applications. Products based on multicrystalline wafers still have the largest market share with thin film products picking up in recent times. Manufacturers of thin film products have increased their production volume. In the meantime, production technology for wafer based solar cells has been improved. With the second generation of tools a trend towards standardization is to be noticed. Both in wafer based as well as in thin film solar cells a number of plasma processes are applied in the production process. These processes include conventional magnetron sputtering or PECVD as well as plasma chemical etch processes. In terms of thin films the portfolio ranges from the rather well known silicon nitrid or ITO films to rather more complex binary films. We will present but a few examples from the afore mentioned applications and discuss open question with respect to vacuum and machine technology.     

Single-graded CIGS with narrow bandgap for tandem solar cells

Multi-junction solar cells show the highest photovoltaic energy conversion efficiencies, but the current technologies based on wafers and epitaxial growth of multiple layers are very costly. Therefore, there is a high interest in realizing multi-junction tandem devices based on cost-effective thin film technologies. While the efficiency of such devices has been limited so far because of the rather low efficiency of semitransparent wide bandgap top cells, the recent rise of wide bandgap perovskite solar cells has inspired the development of new thin film tandem solar devices. In order to realize monolithic, and therefore current-matched thin film tandem solar cells, a bottom cell with narrow bandgap (~1 eV) and high efficiency is necessary. In this work, we present Cu(In,Ga)Se₂ with a bandgap of 1.00 eV and a maximum power conversion efficiency of 16.1%. This is achieved by implementing a gallium grading towards the back contact into a CuInSe₂ base material. We show that this modification significantly improves the open circuit voltage but does not reduce the spectral response range of these devices. Therefore, efficient cells with narrow bandgap absorbers are obtained, yielding the high current density necessary for thin film multi-junction solar cells.     

A Highly Versatile and Adaptable Artificial Leaf with Floatability and Planar Compact Design Applicable in Various Natural Environments

As a promising means of solar energy conversion, photovoltaic (PV) cell‐based electrolysis has recently drawn considerable attention for its effective solar fuel generation; especially the generation of hydrogen by solar water splitting. Inspired by remarkable accomplishments in enhancing the solar‐to‐hydrogen conversion efficiency, various efforts have aimed at fostering convenient and practical uses of PV electrolysis to make this technology ubiquitous, manageable, and efficient. Here, the design and function of a monolithic photoelectrolysis system—a so‐called artificial leaf—for use in various environments are highlighted. The uniquely designed artificial‐leaf system facilitates an unbiased water‐splitting reaction by combining superstrate PV cells in series with single‐face electrodes in a compact 2D catalytic configuration. Floatability is a new feature of the water‐splitting artificial leaf; this feature maximizes solar light utilization and allows for easy retrieval for recycling. Additionally, its planar design enables operation of the device in water‐scarce conditions. These characteristics endow the artificial leaf with versatility and a high adaptability to natural environments, widening the applicability of the device.     

Leistungsfähige Dünnschicht‐Beschichtung für die Photovoltaik

High‐performance thin‐film coating for photovoltaic applications The thin‐film photovoltaics market is large and is expected to grow continuously. Due to its huge potential regarding cost reduction and cell efficiency improvement, sputter‐etched ZnO:Al‐based TCO can make a sustainable contribution to achieve grid parity. One of the most promising approaches here is the large scale volume manufacturing of sputter‐etched TCO glass for thin film silicon solar cells. VON ARDENNE's leading process knowhow, applied to the highly productive and reliable PIA|nova coating system, allows for cost effective production and flexible adaptation of customer specific TCO requirements.     

Pulvermetallurgisch hergestellte Sputtertargets

Sputtering Targets Made by Powder Metallurgy for CIGS Thin Film Photovoltaics Thin film deposition by magnetron sputtering is an important process step in the manufacturing of CIGS thin film solar cells. They are based on the semiconductor Cu(In,Ga)Se₂ and comprise a back contact of molybdenum. This article describes the manufacturing and application of sputtering targets made from molybdenum (Mo), MoNa and CuGa used in the CIGS production. The powder‐metallurgical manufacturing route for sputtering targets is introduced using Mo as example. Sputtering targets produced by pressing‐sintering‐deformation show the highest material purity and density. MoNa targets are a composite material made from a sodium (Na) compound and Mo powder. Sputtering a MoNa layer is an easy solution to dope the CIGS absorber with small amounts of Na. CuGa targets made by powder metallurgy show a much finer microstructure compared to casted targets, which results in a smooth sputtering surface and a more homogeneous lateral film composition.     

薄膜太阳能电池的技术特点及前景展望

本文着重阐述了非晶硅薄膜电池、多晶硅薄膜电池、铜铟硒系薄膜太阳能电池以及染料敏化二氧化钛薄膜太阳能电池生产技术方法以及研究方向，特别介绍了一些薄膜太阳能电池的实验室样品和组件的最高光电转化效率。并从材料、工艺与转换效率等方面讨论了它们的优势和不足之处。同时介绍了国内外薄膜太阳电池研究的进展，展望了薄膜太阳能电池的发展前景。     

Nanocomposite three-dimensional solar cells obtained by chemical spray deposition

The present study is focused on low-cost preparation of thin film TiO2/CuInS2 nanocomposite three-dimensional (3D) solar cells. With the aid of a simple spray deposition method, we have been able to obtain 3D solar cells, with a remarkable energy conversion efficiency of 5%. The new 3D solar cell design has the potential to breakdown the price barrier and to open up new production technologies for low-cost photovoltaic solar cells.     

Efficiency simulations of thin film chalcogenide photovoltaic cells for different indoor lighting conditions

Photovoltaic (PV) energy is an efficient natural energy source for outdoor applications. However, for indoor applications, the efficiency of PV cells is much lower. Typically, the light intensity under artificial lighting conditions is less than 10 W/m² as compared to 100-1000 W/m² under outdoor conditions. Moreover, the spectrum is different from the outdoor solar spectrum. In this context, the question arises whether thin film chalcogenide photovoltaic cells are suitable for indoor use. This paper contributes to answering that question by comparing the power output of different thin film chalcogenide solar cells with the classical crystalline silicon cell as reference. The comparisons are done by efficiency simulation based on the quantum efficiencies of the solar cells and the light spectra of typical artificial light sources i.e. an LED lamp, a “warm” and a “cool” fluorescent tube and a common incandescent and halogen lamp, which are compared to the outdoor AM 1.5 spectrum as reference.     

Unravelling complex nature of CdS/CdTe based thin film solar cells

Thin film solar cells based on CdS/CdTe hetero-structure has shown a drastic improvement changing from 16.5 to 22.1% efficiency during a short period of time from ~2013 to ~2016. This has happened in the industrial environment and the open research in this field has stagnated over a period of two decades prior to ~2013. Most of the issues of this hetero-structure were not clear to the photovoltaic (PV) community and research efforts should be directed to unravel its complex nature. Issues related to materials, post-growth treatment, chemical etching prior to metallisation and associated device physics are the main areas needing deeper understanding in order to further develop this device. After a comprehensive research programme in both academia and in industry on these materials, surfaces and interfaces and fully fabricated devices over a period of over three decades by the main author, the current knowledge as understood today, on all above mentioned complex issues are presented in this paper. Full understanding of this structure will enable PV developers to further improve the conversion efficiency beyond 22.1% for CdS/CdTe based solar cells.