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[en] Full text: Grand challenges to create new front metallization techniques in photovoltaics focus considerable attention on LIFT approach. This alternative method aims to overcome the limitations of the well-established and mature screen-printing technique. Such limitations are for instance: restrictions in the grid pattern design, high temperature steps, and poor aspect ratio of the line contact. Although different new front contact metallization concepts have been studied like ink-jet printing, light induced plating or photolithography, etc., most of them require relatively complicated or expensive processing steps and are not attractive for industrial production. As a result it is desirable to find innovative metallization techniques to improve the cell efficiency without significantly increasing the cost. As mentioned before, a very promising metallization concept, which can be implemented in production lines, is based on a single-step LIFT from thick film Ag inks. But many challenges remain before obtain high-quality, robust and high performance LIFT contacts formation and it is required a fully theoretical and experimental assessment. With this intention the direction which is followed by Lasers, Plasmas and Photonic Processes Institute (LP3) was to develop and optimize LIFT technique to create front side metallization for photovoltaic applications. This paper presents the results of a study of LIFT technique to create high quality and good relation aspect contacts prepared from thick Ag-based inks. The process provides precision deposits of silver inks films onto a working substrate. The beam of a picosecond pulsed laser (Continuum Leopard SS-10-SV Nd:YAG, 10hz, 50ps, at 355 nm third harmonic) is imaged on the donor. The receiver substrates are located on micrometer translation systems (x, y, z). The laser pulses interact with the liquid film and propel the ink away from the substrate. The ejected material exhibits different regime of ejection depending of the viscosity of the liquid. We focus on this paper on the ejection of high viscosity paste. For successful LIFT front contact formation a full understanding of the fluid dynamics of the accelerating ink films is critical. Finally, complete morphological study was carried out with Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) spectrometry and Confocal microscopy. The fluid dynamics of the ejected material has been studied by time-resolved imaging technique. The results and fundamental investigations of the processes underlying the technique illustrate the role played by different laser parameters in the evolution of microstructure and electrical properties of the deposited material. (author)
[en] Recent advances in science and technology of materials fabrication, engineering of work functions, and micrometer gap machining between emitter and collector are making thermionic conversion/converter (TEC) of solar energy an emerging technology. As the converter is the lightest of all devices with highest direct power conversion density (per unit area of the converting surface), it has, potential for substituting photovoltaic technology to a large extent and for deployment in space as a power source. This article summarizes the current efforts/technologies in the field, and discusses their inherent merits and demerits towards realizing the goal of achieving high conversion efficiency and simulation of performance evaluation of a solar TEC. We also discuss the use of both metals and nanomaterials, critical roles of work functions of both emitter and collector, collector temperature, absorptivity and emissivity of the surfaces, radiation losses, and use of both metals and nanomaterials in the efficiency of conversion of solar energy. We further deal with the role of correcting thermionic emission current density equation in the simulation of solar TEC performance. We discuss briefly the possible methods of space-charge control in future in a solar TEC. (author)
[en] Solar energy is currently one of the great alternatives for the eventual scarcity of energy from fossil fuels. A source without pollution, accessible, inexhaustible and that besides the savings in the generation process can be used in the concept of 'smart grids' generating profit for the excess energy produced. The contextualization of this theme in the teaching of Chemistry and Physics amidst the current moment of containment of expenses promotes the valorization of human knowledge, showing integration between science, necessity and technical evolution. One of the most active areas of research that serves as a background for the interdisciplinary context, uniting concepts of modern physics, energy conservation, conjugated polymers and organic chemistry.(author)
[en] Highlights: No covalent bonds are formed between P3HT and PCBM in the gas phase. Noncovalent bonds involving hydrogens are 90% of the total number of bonds. HX bonds are the more frequent bonds in both P3HT-PCBM isomer. The HH bonds are the second most frequent interactions. In order to cast some light onto the nature of the chemical bonding between a 8-unit oligomer of the poly(3-hexylthiophene) (P3HT) and the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in the two stables isomers reported recently [I. Gutiérrez-González, B. Molina-Brito, A.W. Götz, F.L. Castillo-Alvarado, J.I. Rodríguez, Chem. Phys. Lett. 612, 234 (2014)], we have performed a Bader's quantum theory of atoms in molecules (QTAIM) analysis. According to QTAIM, no covalent bonds are formed between P3HT and PCBM, and hydrogen and stacking interactions account for about 90% and 10% of the total number of bonds between P3HT and PCBM, respectively.
[en] In recent years, composite materials based on organic polymer and inorganic nanoparticles have become promising materials for the manufacture of efficient solar cells on their basis. The effectiveness of such elements is constantly growing due to the use of new materials and the modernization of technologies for their production. However, due to the low cost of materials and ease of production, the cost of such batteries is reduced. At the moment, there are works devoted to the study of the parameters of solar cells based on a P3HT composite with nc-Si nanoparticles introduced. At the same time, the electrical, photoelectric, and optical properties of the composite material itself are practically not investigated. In our work, we include p-type silicon nanocrystals in P3HT at concentrations of 10 and 30% by weight. The behavior of the dark conductivity and photoconductivity of the composites on the proportion of Si nanoparticles indicates that an increase in the proportion of nanocrystals in the P3HT polymer film leads to a significant increase (about 10 times) in both the dark conductivity and photoconductivity. The spectral dependences of photoconductivity showed that the samples have photoconductivity at quanta energies of 1.2 eV, and the samples with Si nanoparticles have photoconductivity at lower energy of quanta. In addition, one can also note an increase in the photoconductivity of the composite by an order of magnitude in the entire spectral range under study. In the course of the study, it was found that the addition of n-type silicon nanoparticles in P3NT at concentrations of 10-30% by weight leads to a noticeable improvement in the electrical and photoelectric properties of the material. The results indicate that the P3HT/nc-Si composite can be considered as a promising material for use in photovoltaics. (authors)
[en] The present study demonstrates the chemical bath deposition of Bi2S3 over previously prepared porous photoanode of SnO2 for solar cell fabrication. Deposition of Bi2S3 onto SnO2 photoanode is carried out at 27 °C for 30, 60 and 120 m, showing structural modification and different Bi/S ratio with increase in deposition time. An enhancement in the optical absorbance is observed as a function of deposition time. The best photovoltaic performance is observed for the deposition time of 30 m. The obtained photovoltaic performance is correlated with the structural, optical and elemental analysis of the sensitized photoanodes, finding a qualitative role of recombination resistance in determining the photoconversion performance. (author)
[en] The non-renewable nature of fossil fuels as an energy source means its future availability is a cause for concern. The world’s energy demand is ever increasing and there is a growing interest in finding alternative renewable, environmentally benign and cheap energy sources like solar energy. This has resulted in the shortage of silicon feedstock for the photovoltaic industry. This is mainly due to the non-availability of a dedicated solar silicon production and the growing demand for silicon feedstock. There has been tremendous research in a quest to develop methods for the production of solar-grade silicon in a cheap and environmentally friendly way. The metallurgical and chemical routes for the production of solar-grade silicon from metallurgical-grade silicon have evolved. The chemical methods are the most researched ones and they are mostly preferred than the metallurgical ones since the former are capable of producing silicon of higher purity. This review discusses some of the available methods so far for the production of solar-grade silicon using metallurgical-grade silicon as a starting material.
[en] Photovoltaic effect or phenomenon is the creation of a voltage and corresponding current in a material upon exposure to light energy following the principle that for every excitation there must be a response. The exposition of a solar cell to incident optical radiation excites the dislodgement of electrons hence the creation of holes and subsequent migration of opposite charges. The amount of voltage that can be generated is a function of the intensity of incident optical radiation and the position of the solar cell to such radiation. Measurements of illumination intensity from halogen and tungsten lamps by a digital lux meter and open circuit voltage, short circuit current as output parameters by volt- amp meter LCD display embedded in the solar power device was carried out. The evaluation of fill factor, maximum power and conversion efficiency as other output parameters in relation to illumination from the sources of light at varying angle and distance were carried out in this study also. The variation of the internal resistance of the cell with light intensity was also investigated. The maximum output voltage and current were realized at angle zero degree when the light ray falls at normal to the cell surface. The two 10 Watts halogen lamp gave the highest illumination intensity of 116lx while the 40 Watt and 60 Watt tungsten lamp placed at 10 cm from the solar cell indicated an intensity of 70lx and 25lx each. The results showed the strongly direct dependency of these parameters on illumination intensity and their inverse dependence on the tilt angle and distance of the illumination source. The internal resistance decreases with increasing intensity while the evaluated fill factor, maximum power and efficiency remain fairly constant but at an average value 0.53, 122mW and 55% respectively. (author)
[en] Conductive polymers are macromolecules that have a conjugated system of π bonds. This feature allows the delocalization of electrons through the molecule and generates the possibility of electrical conduction. Among the first reported conductive polymers we find polyacetylene (PA), poly(p-phenylene) (PPP), poly(p-phenylene vinylene) (PPV), polythiophene (PT), polyaniline (PANI) and polypyrrole (PPy). The discovery of the conductive properties of these polymers led to the quest of applications in electronics and in energy generation. In these areas, systems that meet the current technological needs and have a potential use in satisfying future technological requirements have been developed. The objective of this review article is to give an overview of conductive polymers, reviewing some historical data and demonstrating their importance in technological advancement through their application in photovoltaic cells and electronic devices. (author)
[es]Los polimeros conductores son macromoleculas que presentan un sistema conjugado de enlaces π. Este ordenamiento permite la deslocalizacion de electrones a traves de la molecula y genera la posibilidad de conducir electricidad. Entre los primeros polimeros conductores reportados encontramos al poliacetileno (PA), al poli(p-fenileno) (PPP), al poli(fenilenvinileno) (PPV), al politiofeno (PTf), a la polianilina (PANI) y al polipirrol (PPy). El descubrimiento de las propiedades conductoras de estos polimeros condujo a la busqueda de aplicaciones en electronica y en generacion de energia. En estas areas se han desarrollado sistemas que cumplen con las necesidades tecnologicas actuales y que tienen uso potencial, satisfaciendo necesidades tecnologicas futuras. El objetivo del presente articulo de revision es dar una vision general sobre los polimeros conductores, repasando algunos datos historicos y mostrando su importancia para el avance de la tecnologia mediante su aplicacion en celdas fotovoltaicas y dispositivos electronicos. (autor)
[en] Full text: Laser Induced Forward Transfer (LIFT) is a widely used technique for elegant deposition and patterning of various materials (eg. Metals, oxides, organic substances and even biological material). The most typical attribute of LIFT technique (as presented by many authors) is utilization of short laser pulses with duration from ps to tens of ns with very high energy per pulse. Such approach requires of usage of expensive laser sources. Our work is focused to alternative instrumentation of LIFT - possibilities of usage of continuous wave (CW) lasers for local deposition and patterning of organic semiconductors. The source substrates were prepared as follows: Thin glass slides with sputtered metal layer (gold, platinum, copper, silver - thickness ~ 100 nm) were cleaned and dried. Side with sputtered metal was then covered with a thin layer of purified organic semiconductors - Perylene, Perylene anhydride, Zn and Sm Phthalocyanines, AlQ3 and Fullerene C60, deposited by organic molecular evaporation in high vacuum chamber (10-5 Pa, dep. Rate ~ 0.1-3nm/min, substrate temp. 20 – 300 °C). The temperature of deposition source and substrate was selected for each substance so as to achieve optimal growth rate and to avoid thermal decomposition of materials. In the next step CW laser depositions were carried out from these substrates. The deposition apparatus include micro CNC machine (minimal step adjustable to 300 nm) equipped with the semiconductor laser (405 nm, 10 - 50 mW, spot 6 microns) in continual mode and focusing optics. The distance between source substrate and target (i.e. glass, silicon or alumina sensor substrates) was varied between 1-100 micrometers. Deposition process was held in an inert gas (Argon, Nitrogen) at atmospheric pressure. Morphology and microstructure were studied by optical, electron microscopy and AFM. Chemical composition of deposited structures was studied by FTIR and compared with that of source substances. It was proved that chemical structure of all chosen substances is not affected by this deposition technique. The best lateral resolution of prepared structures was obtained for source layer thickness of 100-150 nm. Employing our CWLIFT technique we are able to achieve precise and reproducible laser transfer of organic semiconductors to the target substrate with lateral structural resolution of 14 microns. Selected substances are widely used in the form of thin film for novel organic photovoltaic devices. CW-LIFT deposition and patterning could improve conversion efficiency and other properties of these devices. We can make an assumption that CW-LIFT technique could be used also for other organic semiconductors used in organic photovoltaics which can be deposited by organic molecular evaporation. (author)