1,721,242 research outputs found
Photopolymers for dye-sensitized solar cells
No full textEnergy and environment have become the two predominant scientific research areas in the 21st century, and in some ways they are closely interconnected. Fossil fuels can no longer represent the predominant energy supply for human being. Their use must be reduced and alternative sustainable energy resources have to be identified and rapidly exploited. In the coming decades, the exploited energy sources will not only affect economy and politics but, in fact, health itself. The most direct and obvious effect derived from the current intensive use of fossil fuels is linked to the global warming caused by greenhouse gas emissions. The World Health Organization has recently estimated an increase of five million patients and 150,000 deaths per year resulting from the recent global temperature increase. Indirect effects are also important, such as the increase of infectious diseases transmitted by insects (especially malaria) and the deterioration of overall health due to malnutrition, as a direct consequence of drought and famine. Finally, the continuous use of fossil fuels boosts global pollution, which in turn significantly increases the mortality for respiratory and cardiovascular diseases. Global energy supply system must be urgently reassessed exploiting the use of clean energy sources. To this purpose, investments for the development of renewable energy resources are increasing worldwide, with particular attention to the most mature technologies such as hydro, wind and solar power. In particular, photovoltaics stands out as the most effective technology to be intensively exploited, especially if one considers that the total solar energy absorbed by Earth in one hour is higher than the overall yearly energy use. Many different photovoltaic devices have been developed over the last sixty years, and the large-scale production of solar panels having good efficiencies has begun in the last decade and is rapidly growing. The major goal is to find a trade-off between efficiency, stability, cost and environmental impact of the solar cells. This has led to a lively scientific research in this direction, in a multidisciplinary environment that includes materials scientists, electronic engineers, technologists and experts of life cycle assessment. The dye-sensitized solar cell (DSSC) is a photoelectrochemical device proposed in 1991, composed of widely available and cheap materials. Due to its ease of manufacture, versatility in the choice of components, good efficiency even in the presence of low irradiation level and adaptability to flexible substrates, DSSC has received considerable attention from the scientific community. However, despite the record efficiency of 13% and the recent large-scale industrial production, DSSCs still suffer from poor long-term stability, mainly due to the presence of the volatile liquid electrolyte as well as photosensitive organic components. In such a scenario, the scope of this PhD Thesis is the development of innovative quasi-solid electrolytes and external coatings where specifically designed polymeric networks are able to impart both high stability and efficiency to the resulting DSSCs. In Chapter 1 the current global energy scenario is thoroughly presented, along with an overview of the technologies developed for the conversion of solar energy into electricity. The physical parameters useful for the evaluation of the photovoltaic device performance are detailed and the state of art efficiencies so far achieved by means of the current technologies are reviewed. Chapter 2 deals with the basic concepts for DSSCs; cell architectures, components and operating principle are detailed. The specific characterization methodologies developed for the study of DSSCs are also described. Chapter 3 is focused on DSSC stability, which represents a key issue of the current solar energy research. The two main strategies to achieve stable DSSCs (i.e., the replacement of liquid electrolytes with polymeric ones and the introduction of external multifunctional polymeric coatings) are reviewed. As regards the preparation of these materials, photopolymerization is presented as one of the most promising technique due to its unique features such as rapidity and environmental friendliness, which are highly desired in a low impact and cheap technology like DSSC. The experimental part of this Thesis deals with the research work carried out on the preparation, characterization and testing of photopolymerized electrolytes and coatings. Both of these components have been investigated by means of an approach that started with the identification of suitable UV-curable monomers, followed by the study of the relationship between materials and devices performance, and concluded with the optimization through the introduction of particular additives able to give the material a multifunctional feature. In Chapter 4 the preparation and characterization techniques used for the fabrication and analysis of cell components and devices are briefly described. The experimental work has been carried out in the Center for Space Human Robotics (Istituto Italiano di Tecnologia, Torino) and in the Department of Applied Science and Technology (Politecnico di Torino). In Chapter 5, UV-crosslinked polymer electrolyte membranes (PEMs) are proposed and demonstrated as efficient and stable DSSC electrolytes. Physico-chemical, thermal, viscoelastic and electrochemical techniques are used to investigate the correlation between chemical structure of PEMs and resulting DSSC performance, with a special focus on the transport phenomena within PEMs as well as at the interface with the cell electrodes. The experimental conditions for the preparation of the polymer electrolyte are optimized by a design of experiments approach, which is used in the DSSC research field for the first time. Light-to-electricity conversion efficiency values of the lab-scale DSSCs assembled with these polymer electrolytes are admirably almost equal to the corresponding liquid cells, moreover a remarkably better long-term stability is obtained. In Chapter 6, a step forward is proposed, where three unconventional approaches are exploited for the successful implementation of photocrosslinked PEMs, namely the fabrication of flexible devices, the preparation of PEMs having a gradient-tailored spatial composition and the in situ photopolymerization of electrolytes containing alternative redox couples. These three themes are definitely innovative in the DSSC field and represent important advances from a technological viewpoint. Since the use of functional fillers has been scarcely considered in the DSSCs literature so far, the idea of improving both cell efficiency and durability by their introduction in PEMs is proposed in Chapter 7. In this respect, metal-organic frameworks (MOF) and nanocellulose are introduced in UV-cured membranes, and their effect on photovoltaic and stability performance is investigated. In particular, a novel bio-sourced filler is demonstrated to cumulatively increase the photocurrent, the photovoltage and the long-term stability of a polymeric lab-scale DSSC. In Chapter 8, the protection of DSSCs from UV radiation and atmospheric agents by the application of photopolymerized coatings is proposed. Multifunctional coatings, able both to convert the harmful UV light into harvestable visible light by downshifting and to confer self-cleaning and water-repellent properties to the external side of the cells are investigated. For the first time, a general approach that simultaneously improves performance and weatherability of organic DSSC devices is presented, and it is noteworthy that these multipurpose coatings are obtained by means of a rapid and up-scalable photopolymerization proces
Polymer electrolytes and perovskites: lights and shadows in photovoltaic devices
No full textPhotoelectrochemical devices for the conversion of sunlight into electricity are experiencing a period of fervour due to the use of new solid-state materials capable of ensuring a durability higher than that of liquid electrolytes-based cells. Dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) are currently contending for the role of leader in the field of third-generation photovoltaic technologies. In particular, such success is attributed to the introduction of polymer electrolytes and perovskites, which have recently contributed to obtaining high conversion efficiencies. This review summarizes the most important results in this field and the strategies developed to maximize DSSCs and PSCs performance. In addition, limitations and disadvantages of polymer electrolytes and perovskites are presented, together with possible strategies aimed at improving the photovoltaic efficiency, reducing the cost and limiting the use of toxic and rare material
Photopolymers as Emerging Advanced Materials for Sustainable Conversion and Storage Energy Devices
No full textThe stability of energy devices is a critical (but often disregarded) issue, since great focus is often devoted to the efficiency records (even if these values rapidly decrease upon time). However, today's research in the energy field must be connected to concepts such as long-term stability, safety and environmental impact. In this work, we present free-radical photopolymerization as an attractive technique for the design and straightforward preparation of polymeric components for different energy devices (both storage and conversion). Photopolymerization represents a very attractive technique to this purpose, since it does not require solvents, catalysts, thermal treatments and purification steps. In the initial section, polymer electrolytes for dye-sensitized solar cells (DSSC) are demonstrated as alternatives to the standard liquid counterparts, using cobalt complexes as redox mediator. In addition, external luminescent and light-cured coatings are developed to further increase cell durability through a combined effect of UV-cutting, down-shifting and self-cleaning. In the second section, electrolytes and light-cured protective coatings are demonstrated for the first time in photoelectrochromic devices, thus leading to smart windows with highly stable characteristics and easy to be manufactured on a large scale. Finally, we show how Na-ion polymer batteries can be considered as an emerging, green and safe solution to the large storage of the electricity produced by solar panel
Fotopolimeri per l'energia: una nuova strategia nel campo di conversione e stoccaggio delle fonti rinnovabili
No full textL'irraggiamento di monomeri reattivi in condizioni blande genera fotopolimeri impiegabili come componenti di celle solari di terza generazione e batterie a ioni litio/sodio. Questa tecnologia sostenibile e a basso impatto migliora la durabilità e la sicurezza di questi dispositivi energetici di largo impieg
Thermoset membranes as electrolytes for Dye Sensitized Solar Cells
No full textDye-sensitized solar cells (DSSCs) have attracted large attention due to their easy fabrication, low cost and high conversion efficiency. One of the major problems limiting the long-term stability of these devices is the volatilization of the liquid electrolytes. To solve this problem and give technological perspectives of DSSCs, many recent studies have been addressed to the preparation of quasi-solid electrolytes. In this work, we highlight the potential of free-radical photopolymerization as a method of preparation of quasi-solid polymer electrolytes
Photopolymers for Grätzel’s solar cells
No full textThe conversion of solar energy by photovoltaic effect is the most quoted reality in the world of renewable resources. As a feasible option for photovoltaic technology to meet the growing energy demand, dye-sensitized solar cells (DSSCs) have attracted much attention due to their low cost, ease of fabrication and good performance. Furthermore, DSSCs are representing an important common ground among synthetic chemistry, polymer science, electrochemistry and industrial scaling-up.
We have recently proposed polymer electrolyte membranes as a promising strategy to solve the poor long-term stability of standard liquid-state DSSCs. Membranes were prepared by a rapid, energy-saving and environment friendly technique of light-induced polymerization, that can find an appropriate location also in the nascent industrial production plants of third generation photovoltaic cells.
The talk will be focused both on special fillers (MOF and nanocellulose) used to increase the light harvesting, and on the introduction of new redox couples, whose compatibility with polymeric matrix and effects on the light-curing process will be detailed. Lastly, the transfer of these polymer electrolytes in flexible devices (one of the most promising ambitions of DSSCs) will be presented
Photoinduced polymerization: An innovative, powerful and environmentally friendly technique for the preparation of polymer electrolytes for dye-sensitized solar cells
No full textDye-sensitized solar cells (DSSCs) have attracted large attention due to their easy fabrication, low cost and high conversion efficiency. One of the major problems limiting the long-term stability of these devices is the volatilization of the liquid electrolytes traditionally used. To solve this problem and improve technological perspectives of DSSCs, many recent studies have been addressed to the preparation of quasi-solid electrolytes, in which a polymer network is able to effectively retain the redox mediator and its additives. In this context, photoinduced polymerization is increasingly proving to be the most effective method of preparation of these polymer electrolytes, since it is a rapid, economic, functional and environmentally friendly process, besides being easily transferable to the industrial scale. This review focuses on the techniques adopted for the preparation of UV-cured quasi-solid electrolytes, on the expedients designed to overcome the inhibition phenomena typical of some photoinitiated mechanisms, and on the evaluation of photoelectric performance obtained in presence of these photopolymer electrolyte
In situ photopolymerization for making DSSC quasi solid electrolytes and assembling the cell
No full textA feasible option for photovoltaic technology is represented by dye-sensitized solar cells (DSSCs): they have low cost, easy fabrication and good performance. The relevant technological drawbacks, i.e. scarce long-term stability, electrolyte evaporation, and permeability to H2O/O2 are mainly due to the presence of a liquid electrolyte. Therefore it was proposed to replace it with (quasi)-solid polymer electrolytes prepared by free-radical photopolymerization. Once the membrane was cured, it was swelled with the I−/I3− electrolyte solution and then assembled with the electrodes (a TiO2 photoanode sensitized with a dye and a transparent photocathode). An accurate characterization of a set of UV-cured membranes highlighted the influence of the chemical structure of the networks and their crosslinking density on the photo-electrochemical performances of the cells. Pursuing this work, in situ photopolymerisation was attempted: the in-situ process is efficient, suitable for scaling-up, can enable the creation of an excellent electrode/electrolyte interface and the sealing of the device. To overcome two major problems, namely the inhibition of radical photocuring by the I−/I3− redox couple and the damaging of the dye under UV-light, a selenocianated-based electrolyte was synthesized on purpose and visible light was used for curing through the photocatode. The DSSC prototype fabricated in this way showed promising photoharvesting properties
Development of multipurpose ethylene oxide based polymer electrolytes for smart and energy efficient devices
No full textWide interest is mounting on polymer electrolytes for application in energy efficient devices such as rechargeable batteries, electrochromics and photovoltaics. Solid polymer electrolytes exhibit unique advantages: mechanical integrity, variety of fabrication methods and intimate electrode/electrolyte interfacial properties. They also improve safety along with more compact and lightweight packaging. Since the discovery of ionic conductivity in alkali metal salt complexes of poly(ethylene oxide), PEO, lot of research was devoted on systems containing lithium salts to be used as electrolytes, particularly in Li-based batteries. In this work, highly ionic conducting PEO-based polymer electrolytes, encompassing lithium salts dissolved in Room Temperature Ionic liquids (RTIL), were successfully prepared via rapid hot-press and subsequently cross-linked via UV irradiation. All the prepared materials were thoroughly characterised in terms of their physical, chemical and morphological properties and tested for ionic conductivity, electrochemical stability and cycling performances. The UV-curing process on such materials led to the production of elastic and resistant polymer electrolyte membranes. The degree of PEO crystallinity was greatly reduced down to the amorphous state by addition of lithium salt and RTIL and UV-induced cross-linking process. As a consequence, a noticeably increased ionic conductivity was registered (> 10-4 Scm-1 at RT). The polymer electrolyte demonstrated a very stable interfacial stability versus lithium metal and a very wide electrochemical stability window (0-5.5 V vs. Li). In the presence of such an electrolyte, the laboratory-scale devices showed remarkable performances, only slightly lower than those using liquid electrolyte, respect to which demonstrated a much greater durability. The obtained findings demonstrate that our proposed preparation can provide a new, easy and low cost approach to fabricate polymer electrolytes with remarkable performance for the next generation of advanced flexible energy production and storage device
Towards green, efficient and durable quasi-solid dye-sensitized solar cells integrated with a cellulose-based gel-polymer electrolyte optimized by a chemometric DoE approach
No full textAn innovative biopolymer composite electrolyte for dye-sensitized solar cells (DSSCs), obtained by quasi-solidifying an indigenous liquid electrolyte containing supporting salts and I3−/I− redox couple with a mixture of polyethylene oxide (PEO) and carboxymethyl cellulose sodium salt (CMC) is proposed. This is the first ever report indicating the useful aspects of CMC as a component in the electrolyte of a photovoltaic device and the requisite parameters are thoroughly investigated. Moreover, the performances of the lab scale quasi-solid devices are presented by means of a combined photovoltaic-chemometric approach, definitely innovative for the study of polymer based electrolytes for DSSCs. We also present the durability of the devices inherited by different PEO : CMC ratios as well as the response of the cells to various wavelengths and irradiation intensities. The intriguing photovoltaic-chemometric approach allows developing a device with efficiencies up to 5.18% under 1 sun irradiation ([similar]7% under 0.4 sun). The cumulative effect by the strategic components employed in the gel-polymer electrolyte demonstrates an outstanding durability with an excellent efficiency as high as 98% even after 250 h of extreme aging condition
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