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.     

Rückseitenmetallisierung Wafer‐basierter Si‐Solarzellen mittels EB‐PVD

Back Side Metallization of Wafer Based Silicon Solar Cells by Means of Electron Beam Evaporation Electron beam evaporation is an innovative vacuum deposition technology regarding the wafer backside metallization of crystalline silicon solar cells. The motivation for the consideration of electron beam evaporation as cell finishing step is based on the one hand on the competition with thin film photovoltaic modules and on the other on the remarkable cost reduction potential by applying EB‐PVD (Electron Beam Physical Vapor Deposition). This article presents a highly productive coater concept and gives an explanation of important aspects for the adaption of the coater concept to typical solar cell features. Various PVD technologies are compared concerning their possible use as wafer backside metallization method. Challenges and chances of the introduction of EB‐PVD in the wafer based solar cell production are considered.     

Alternative materials and processing techniques for optimized nanostructures in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) represent an exciting application of nanotechnology and offer an appealing alternative to conventional solar cells based on photovoltaic devices, with significantly reduced production and material costs. However, further improvements are required to enhance the commercial viability of these solar cells. These improvements may be achieved through the careful manipulation of the structure at the nanoscale and the application of novel processing techniques, which may help to increase the efficiency of these solar cells, improve the ease of manufacture and allow the production of flexible, solid-state solar cells. For example, the use of a nanometre-thick coating of an insulating oxide over the semiconducting film in these solar cells may reduce recombination losses. Also, selective heating techniques such as microwave heating may assist in the production of efficient solar cells on polymer, rather than glass, substrates, by allowing a rapid heat treatment to be applied to the titanium dioxide film at a higher temperature than would be possible with conventional heating. Some novel approaches to the production of semiconducting thin films for dye-sensitized solar cells, as well as the use of alternative materials and nanostructures, are reviewed.     

薄膜太阳电池用TCO薄膜制造技术及其特性研究

阐述了玻璃衬底、柔性衬底透明导电氧化物薄膜(Transparent conductive oxides-TCO)以及硅基薄膜太阳电池应用方面的最新研究成果。绒面结构可以提高薄膜太阳电池效率和稳定性并降低生产成本。磁控溅射技术和LP-MOCVD技术是制造绒面结构ZnO-TCO薄膜(例如"弹坑"状和"类金字塔"状表面)的主流生长技术;高迁移率TCO薄膜(IMO、IWO、ZnO∶Ga等)以及柔性衬底TCO薄膜是研究开发的重点。     

Roll-to-roll plasma deposition machine for the production of tandem amorphous silicon alloy solar cells

A roll-to-roll plasma deposition machine for depositing multilayered amorphous alloys has been developed. The plasma deposition machine has multiple deposition areas and processes a stainless steel substrate 16 in wide continuously. Amorphous photovoltaic thin films (less than 1 μm thick) with a six-layer structure (p-i-n-p-i-n) are deposited continuously in a single pass onto a roll of stainless steel substrate 16 in wide and 1000 ft long. Mass production of low cost tandem solar cells utilizing roll-to-roll processes is now possible. A commercial plant utilizing this plasma deposition machine for manufacturing tandem amorphous silicon alloy solar cells is now in operation.     

Towards high efficiency thin film solar cells

As an alternative to single crystal silicon photovoltaics, thin film solar cells have been extensively explored for miniaturized cost-effective photovoltaic systems. Though the fight to gain efficiency has been severely engaged over the years, the battle is not yet over. In this review, we comb the fields to elucidate the strategies towards high efficiency thin films solar cells and provide pointers for further development. Starting from the photoelectron generation, we look into the fundamental issues in photoelectric conversion processes, including light harvesting and charge handling (separations, transportations and collections). The emerging organic-inorganic halide perovskite systems, as well as the rapidly developed polycrystalline inorganic systems, organic photovoltaics and amorphous silicon cells are discussed in details. The biggest bottleneck for the cost-effective polycrystalline inorganic cells is the composition sensitivity and deep defects; for amorphous silicon cells, it is the quantum of the dangling bonds; for organic cells, it is the low charge carrier mobility and high exciton binding energy; and for perovskite cells, it is the environmental degradation and the controversial mechanisms of generation of I-V hysteresis. Strategies of light harvesting and charge handling as well as directions to break the bottlenecks are pointed out.     

Mit dünnen Schichten durch vier Jahrzehnte

Thin films through four decades – How they changed the world The 30th anniversary of the journal “Vacuum in research and practice” is accompanied by a brief journey through the world of thin films and their impact on our life during the past decades. Around 40 years ago coating processes had been ready to find their way into mass markets related to large areas and quantity of substrates. Reduction of friction, wear and corrosion on tools and machine components, architectural glass, optical and magnetic data storage media, displays, touch panels and solar cells have been the most important application areas during the past four decades. Often ecxiting new products (like the CD) caused a paradigm change in the design of coating machines, or a milestone in process technology (like Pulse Magnetron Sputtering) enabled new applications. In this contribution several decades of thin film technology will pass in fast motion. The article reflects the perception of someone having experienced 35 very exciting years in industrial development as well as applied research related to thin films and their deposition. Certainly this perception is subjective and incomplete.     

Properties of plasma-produced amorphous silicon governed by parameters of the production,transport and deposition of Si and SiHx

Amorphous silicon thin films, which are a fundamental material for photovoltaic applications, can be prepared by plasma chemical processes. Four types of gas discharges, namely r.f. sputtering, d.c. glow discharge, arc and corona discharge, have been investigated to determine their particular characteristics as plasma chemical processes for the deposition of amorphous silicon. By determining the parameters of the plasmas and the conditions of the specific discharge by optical emission spectroscopy and by mass spectroscopy we can control the reproducibility of the plasma state and obtain defined variations in the generated species Si and SiH which constitute the layer. Analyses of film properties show high reproducibility. Moreover, the properties of the films reflect the plasma parameters as well as the deposition conditions.     

陷光结构在GaAs薄膜太阳电池中的应用

陷光结构由于其独特的光学特性,在光伏器件中发挥的作用越来越重要。目前硅基太阳电池中陷光结构的应用很常见,然而在GaAs薄膜太阳电池中陷光结构的报道并不多。详细介绍了陷光结构的原理及其在GaAs薄膜电池中的研究现状和应用情况。综述了GaAs薄膜太阳能电池中常用的三类陷光结构:正面陷光结构(包括纳米颗粒、纳米线、纳米锥等)、背面陷光结构(如镜面背反射层)以及混合陷光结构。大量研究表明,陷光结构的使用可以进一步提高GaAs薄膜电池的光电转换效率,一定程度上达到降低电池生产成本的目的。     

Plasma und Dünne Schichten

Plasma and thin films for lighting application Thin films play an important role in the lighting industry. Well known products are reflectors with simple aluminium coating or with dichroic coatings for cold light mirrors. Especially for energy saving applications special halogen bulbs are coated with a transparent hot mirror that increases the overall efficiency up to 50 % while keeping the positive properties of halogen lighting like color, color rendering index, start up performance and others unchanged. Special thin film applications realize color filters, IR filters, UV filters or color conversion filters. All these processes are vacuum processes that work with plasma assistance. The most prominent technologies for cost effective production are the PICVD processes (former development of SCHOTT AG in cooperation with Auer Lighting) and the Microdyn® technology from DSI, Santa Rosa.     

Sulfosalts — A new class of compound semiconductors for photovoltaic applications

A short historical outline of sulfosalts with respect to their mineralogical origin and their possible technical applications is given. The high number of more than 200 species results from their chemical and structural definition. The modular crystal structures of sulfosalt compounds base on superstructures of diverse construction units. Physical properties of mineral samples as well as deposited thin films show promising results with respect to photovoltaic application. As a proof of concept, first sulfosalt thin film solar cells were prepared. The efficiency of this cell is reported to be 1%. Further efforts will be done to improve 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.     

2.16 Technology of large area Cu2SCdS solar cells

Solar energy can be converted in different ways: the most attractive application is the direct conversion of solar radiation to electricity. For large scale application large area photovoltaic devices are necessary. Highly efficient solar cells can be produced on the basis of thin semiconducting films. An automized pilot line production for CdS layers, which are evaporated under high vacuum conditions, and their subsequent treatment to get an encapsulated thin film solar cell, are described. Investigation methods and a theoretical model of the heterojunction are reported.     

Progress and Perspectives of Thin Film Kesterite Photovoltaic Technology: A Critical Review

The latest progress and future perspectives of thin film photovoltaic kesterite technology are reviewed herein. Kesterite is currently the most promising emerging fully inorganic thin film photovoltaic technology based on critical raw‐material‐free and sustainable solutions. The positioning of kesterites in the frame of the emerging inorganic solar cells is first addressed, and the recent history of this family of materials briefly described. A review of the fast progress achieved earlier this decade is presented, toward the relative slowdown in the recent years partly explained by the large open‐circuit voltage (V_OC) deficit recurrently observed even in the best solar cell devices in the literature. Then, through a comparison with the close cousin Cu(In,Ga)Se₂ technology, doping and alloying strategies are proposed as critical for enhancing the conversion efficiency of kesterite. In the second section herein, intrinsic and extrinsic doping, as well as alloying strategies are reviewed, presenting the most relevant and recent results, and proposing possible pathways for future implementation. In the last section, a review on technological applications of kesterite is presented, going beyond conventional photovoltaic devices, and demonstrating their suitability as potential candidates in advanced tandem concepts, photocatalysis, thermoelectric, gas sensing, etc.     

Effect of ZnO film deposition methods on the photovoltaic properties of ZnO–Cu2O heterojunction devices

The effect of ZnO film depositions using various film deposition methods such as magnetron sputtering (MSP), pulsed laser deposition (PLD) and vacuum arc plasma evaporation (VAPE) on the photovoltaic properties of ZnO–Cu₂O heterojunction solar cells is described in this report. In addition, the relationship between the resulting photovoltaic properties and the film deposition conditions such as supply power and substrate arrangement was investigated in Al-doped ZnO (AZO)–Cu₂O heterojunction devices fabricated using AZO thin films prepared by d.c. magnetron sputtering (d.c.MSP) or r.f. magnetron sputtering (r.f.MSP). The results showed that the measured photovoltaic properties of devices fabricated with films deposited on substrates oriented perpendicular to the target were better than those of devices fabricated with films deposited on substrates oriented parallel to the target. It was also found that ZnO film depositions under conditions where a relatively weaker oxidizing atmosphere was used yield better properties than films derived from MSP, which utilizes a high-density and high-energy plasma. Using VAPE and PLD, for example, high efficiencies of 1.52 and 1.42%, respectively, were obtained under AM2 solar illumination in devices fabricated at a substrate temperature around 200 °C.     

Dünnschichtsolarzellen

Thin Film Solar Cells The direct conversion of sunlight into electricity — photovoltaics (PV) — has emerged as a strongly growing market during the past years. Today, more than 80 % of the world market is supplied by solar modules based on mono‐ or polycrystalline silicon wafers. Thin‐film solar cells promise significantly lower costs for photovoltaic energy conversion, and thus will probably dominate the PV‐market in the future. Consequently, the production of thin film solar cells will lead to key technologies of the 21^st century. This article addresses the three most advanced types of thin‐film cells describing the status of these technologies at the laboratory level, in pilot production, and in first production lines. The challenges along the way from laboratory developments towards mass production are discussed, fo cusing on the central role of the vacuum‐based technologies applied for thin film deposition.     

Ultrafast deposition of silicon nitride and semiconductor silicon thin films by hot wire chemical vapor deposition

The technology of Hot Wire Chemical Vapor Deposition (HWCVD) or Catalytic Chemical Vapor Deposition (Cat-CVD) has made great progress during the last couple of years. This review discusses examples of significant progress. Specifically, silicon nitride deposition by HWCVD (HW-SiN_x) is highlighted, as well as thin film silicon single junction and multijunction junction solar cells. The application of HW-SiN_x at a deposition rate of 3 nm/s to polycrystalline Si wafer solar cells has led to cells with 15.7% efficiency and preliminary tests of our transparent and dense material obtained at record high deposition rates of 7.3 nm/s yielded 14.9% efficiency. We also present recent progress on Hot-Wire deposited thin film solar cells. The cell efficiency reached for (nanocrystalline) nc-Si:H n-i-p solar cells on textured Ag/ZnO presently is 8.6%. Such cells, used in triple junction cells together with Hot-Wire deposited proto-Si:H and plasma-deposited SiGe:H, have reached 10.9% efficiency. Further, in our research on utilizing the HWCVD technology for roll-to-roll production of flexible thin film solar cells we recently achieved experimental laboratory scale tandem modules with HWCVD active layers with initial efficiencies of 7.4% at an aperture area of 25 cm².     

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.     

Plasmachemisches Ätzen und Beschichten bei Atmosphärendruck

Atmospheric pressure plasma‐chemical etching and deposition. Application in crystalline silicon photovoltaics. For industrial processing of wafer based crystalline silicon solar cells a variety of different technologies are applied. The combination of these requires a complex wafer handling; increasing not only investment costs, but also the risk of wafer breakage. Application of plasma technologies offers the possibility to manufacture crystalline silicon solar cells without any wet chemical or vacuum processes. At Fraunhofer IWS all etching steps necessary for the production of solar cells and the deposition of silicon nitride as passivation and anti‐reflection coating were demonstrated successfully using atmospheric pressure plasma technologies.     

Carbon nanotube films by filtration for nanotube-silicon heterojunction solar cells

Carbon nanotube films with high nanotube loading were prepared using a vacuum filtration method and their photovoltaic properties as semi-transparent conducting electrodes in nanotube-silicon heterojunction solar cells were investigated. The correlation between the power conversion efficiency of the solar cells and the figure of merit (FM) of the films were obtained. The maximum efficiencies (up to 1.5%) were found for those cells using the films with highest FMs and transmittances. For comparison, the photovoltaic performance of a self-assembled nanotube thin film of high transmittance (91%) was tested and the corresponding solar cell showed a conversion efficiency of ∼4%. This work provides guidance for future improvement on the photovoltaic properties of nanotube films as window electrode materials.