The History of Photovoltaics with Emphasis on CdTe Solar Cells and Modules

Among thin-film photovoltaic technology, cadmium telluride (CdTe) has achieved a truly impressive development that can commercially compete with silicon, which is still the king of the market. Solar cells made on a laboratory scale have reached efficiencies close to 22%, while modules made with fully automated in-line machines show efficiencies above 18%. This success represents the result of over 40 years of research, which led to effective and consolidated production processes. Based on a large literature survey on photovoltaics and on the results of research developed in our laboratories, we present the fabrication processes of both CdTe polycrystalline thin-film solar cells and photovoltaic modules. The most common substrates, the constituent layers, their interaction, the interfaces and the different “tricks” necessary to obtain highly efficient devices will be analyzed. A realistic industrial production process will be analytically described. Moreover, environmental aspects, end-of-life recycling and the life cycle assessment of CdTe-based modules will be deepened and discussed

Polycrystalline Cu(InGa)Se2/CdS Thin Film Solar Cells Made by New Precursors

In the last five years photovoltaic modules production continued to be one of the rapidly growing industrial sectors, with an increase well in excess of 40% per year. This growth is driven not only by the progress in materials and technology, but also by incentives to sup\u2010 port the market in an increasing number of countries all over the world. Besides, the in\u2010 crease in the price of fossil fuels in 2008, highlighted the necessity to diversify provisioning for the sake of energy security and to emphasize the benefits of local renewable energy sour\u2010 ces such as solar energy. The high growth was achieved by an increase in production capaci\u2010 ty based on the technology of crystalline silicon, but in recent years, despite the already very high industrial growth rates, thin film photovoltaics has grown at an increasingly fast pace and its market share has increased from 6% in 2006 to over 12% in 2010. However, the ma\u2010 jority of photovoltaic modules installed today are produced by the well-established technol\u2010 ogy of monocrystalline and polycrystalline silicon, which is very close to the technology used for the creation of electronic chips. The high temperatures involved, the necessity to work in ultra-high vacuum and the complex cutting and assembly of silicon "wafers", make the technology inherently complicated and expensive. In spite of everything, silicon is still dominating the photovoltaic market with 90% of sales. Other photovoltaic devices based on silicon are produced in the form of "thin films" or in silicon ribbons; these devices are still in the experimental stage

Silane-Mediated Expansion of Domains in Si-Doped κ-Ga2O3 Epitaxy and its Impact on the In-Plane Electronic Conduction

Unintentionally doped (001)-oriented orthorhombic κ-Ga2O3 epitaxial films on c-plane sapphire substrates are characterized by the presence of ≈ 10 nm wide columnar rotational domains that can severely inhibit in-plane electronic conduction. Comparing the in- and out-of-plane resistance on well-defined sample geometries, it is experimentally proved that the in-plane resistivity is at least ten times higher than the out-of-plane one. The introduction of silane during metal-organic vapor phase epitaxial growth not only allows for n-type Si extrinsic doping, but also results in the increase of more than one order of magnitude in the domain size (up to ≈ 300 nm) and mobility (highest µ ≈ 10 cm2V−1s−1, with corresponding lowest ρ ≈ 0.2 Ωcm). To qualitatively compare the mean domain dimension in κ-Ga2O3 epitaxial films, non-destructive experimental procedures are provided based on X-ray diffraction and Raman spectroscopy. The results of this study pave the way to significantly improved in-plane conduction in κ-Ga2O3 and its possible breakthrough in new generation electronics. The set of cross-linked experimental techniques and corresponding interpretation here proposed can apply to a wide range of material systems that suffer/benefit from domain-related functional properties

Riociguat treatment in patients with chronic thromboembolic pulmonary hypertension: Final safety data from the EXPERT registry

Objective: The soluble guanylate cyclase stimulator riociguat is approved for the treatment of adult patients with pulmonary arterial hypertension (PAH) and inoperable or persistent/recurrent chronic thromboembolic pulmonary hypertension (CTEPH) following Phase

CdTe-Based Photodetectors and Solar Cells

In this chapter we will show how much appreciated were the electro-optical characteristics of one of the most widely used semiconductors of the II-VI family, Cadmium Telluride or CdTe. High quality single crystals with industrially appreciable dimensions have been easily obtained since the beginning of the CdTe epopee. Exploiting its very high transparency in the mid-infrared it was firstly employed as window for i.r. laser applications. Its role, as a material for developing electro-optical modulators needed for the evolution of power CO2-based lasers, was crucial. In more modern times, with the advent of nanotechnologies, CdTe has found considerable success as a UV-Vis photodetector if used in the form of dots, ribbons, belts and, more in general, when it is possible to exploit quantum confinement in reduced dimensions. But where CdTe has been most successful is in the photovoltaic field, where solar cells and photovoltaic modules, with conversion efficiency greater than 22% and 19% respectively, have been made. To date, among thin-film technologies, CdTe-based modules occupy the first place on the market and more than 8% globally. We will talk about this and much more in the rest of this chapter by going into the detail of the photodetectors and, mainly, of the solar cells, revealing the smartest tricks normally used to make these devices sustainable, efficient and cost-effective

The History of Photovoltaics with Emphasis on CdTe Solar Cells and Modules

Among thin-film photovoltaic technology, cadmium telluride (CdTe) has achieved a truly impressive development that can commercially compete with silicon, which is still the king of the market. Solar cells made on a laboratory scale have reached efficiencies close to 22%, while modules made with fully automated in-line machines show efficiencies above 18%. This success represents the result of over 40 years of research, which led to effective and consolidated production processes. Based on a large literature survey on photovoltaics and on the results of research developed in our laboratories, we present the fabrication processes of both CdTe polycrystalline thin-film solar cells and photovoltaic modules. The most common substrates, the constituent layers, their interaction, the interfaces and the different “tricks” necessary to obtain highly efficient devices will be analyzed. A realistic industrial production process will be analytically described. Moreover, environmental aspects, end-of-life recycling and the life cycle assessment of CdTe-based modules will be deepened and discussed

Emerging and Evolving Technology in Colon and Rectal Surgery

Minimally invasive surgery has changed the way we manage many colon and rectal pathologies. Multiple techniques, from straight laparoscopic procedures, to hand-assisted and single-port techniques are available, requiring surgeons to go through various learning curves. Robotic surgery is a relatively novel technique in general surgery which appears to hold most promise for rectal resection. Laparoscopic rectal procedures are difficult, and even in experienced hands, conversion rates are around 17%. Robotic surgery may be a point of difference in these cases, despite a long learning curve and higher costs. This article will describe the role of robotics in colorectal surgery. Room set up, port placement, and docking strategies will be described for common procedures, with emphasis on a hybrid robotic low anterior resection

CdTe solar cells by low temperature processes

ABSTRACT:CdTe polycryst. thin film solar cells have a strong potential in scalability. They have shown long-term stable performance and high efficiency up to 16.5% under AM1.5 illumination. Amongst several attractive features, high chem. stability of CdTe and a simple compd. formation are the most important ones for large area prodn. of solar modules. A further simplification has been done by substituting the CdCl2 step by treating CdTe films in an atm. contg. a non toxic gas that is inert at room temp., like HCF2Cl, that belongs to the Freon family. The treatment temp. is typically 400°C, for a few minutes and in an atm. contg. Cl, typically 100 mbar of Ar contg. 15% of HCF2Cl. The change in the morphol. of CdTe films after treatment is very similar to that obtained with CdCl2 treatment and an increase in the size of small grains is always obsd. This process has been applied by N. Romeo et al. on CdTe deposited by close-spaced sublimation (CSS) with very interesting results (15.8% efficiency). The application of the regular CdCl2 treatment and of this novel "activation process" on low and high temp. processed solar cells will be described Moreover, there are new promising device configurations like bifacial solar cells, ultra-thin solar cells and flexible devices. The highest efficiencies in CdTe solar cells have been obtained using CSS deposition method, which requires a high substrate temp. (500÷550 °C). Instead, conventional phys. vapor deposition (PVD) process where CdTe is evapd. in a high vacuum evapn. (HVE) system at lower substrate temps. (typically 300°C) has provided solar cells with efficiencies of more than 12%. For these reasons HVE process is attractive for a very simple in-line deposition of large area CdTe solar modules on soda-lime glass substrates, as well as on polymer foils thereby facilitating the roll-to-roll manufg. of flexible solar modules. Flexible CdTe/CdS solar cells of 11% efficiency in superstate and 7% efficiency in substrate configurations have been developed with a "lift-off" approach. However, roll-to-roll manufg. is desired in future. Therefore, flexible superstate solar cells have also been directly grown on com. available polyimide foils. Solar cells with AM1.5 efficiency of 12.4% on Upilex foils (highest efficiency recorded for flexible CdTe cell) have been developed. A different possibility in making flexible CdTe solar cells is to use a metal foil as substrate, provided that the stacks would be deposited in the opposite order to have light coming from the top and not through the substrate (the so-called "substrate configuration" process). However making a CdTe photovoltaic device in inverted structure implies a variety of different scientifical issues, that will be addressed. The latest development is the application of a transparent conducting oxide (TCO) ITO as a back elec. contact on CdTe leading to first bifacial CdTe solar cells, which can be illuminated from either or both sides. Accelerated long term stability tests show that light soaking improves the efficiency of CdTe solar cells with ITO back contacts and performance does not degrade. Such solar cells are attractive for tandem solar cells though larger band gap absorbers based on CdTe would be desired. Application of light tapping concepts can be employed to reduce the CdTe layer thickness to below 1 μ