5363210-31750-816610-31750GUJARAT TECHNOLOGICAL UNIVERSITY
V.V.P. ENGINEERING COLLEGE, RAJKOT
DYE SENSITIZED SOLAR CELL (DSSC): A NEW GENERATION OF SOLAR CELL USING NANOTECHNOLOGY
YASH BHARODIYA (150470139002)
MEERA MANAVADARIYA (150470139011)
Dr. Jaysukh H. Marakana
Department of Nanotechnology
V.V.P. ENGINEERING COLLEGE
In fulfilment for the award of the degree of
BECHELOR OF ENGINEERING in
We have taken efforts in this project. However, it would not have been possible without the kind support and help of many individuals and organizations. We would like to extend my sincere thanks to all of them.
We are highly indebted to Dr Jaysukh Marakana for their guidance and constant supervision as well as for providing necessary information regarding the project & also for their support in completing the project.
We would like to express our gratitude towards our parents & member of V.V.P. Engineering College, Rajkot for their kind co-operation and encouragement which helped me in completion of this project.
We would like to express our special gratitude and thanks to Meet Moradiya et al. for giving us such attention and time.
Our thanks and appreciations also go to our colleague in developing the project and people who have willingly helped our out with their abilities.
Chapter 1. Introduction
Chapter 2. DSSC: Dye sensitized solar cell
Chapter 3. Fabrication of Solar Cell
Chapter 4. Design engineering canvass
Chapter 5. Summary
CHAPTER 1: INTRODUCITON
What is Solar Cell?
A solar cell, also known as photovoltaic cell, is an electrical device or an instrument which is used to converts the light energy directly into electricity with the help of photovoltaic effect.
Photovoltaic effect: Photovoltaic effect is a physical and chemical phenomenon. It is a form of photoelectric cell. It can be defined as an instrument whose electrical characteristics i.e. current (I), voltage (V) or resistance (R) may vary when light is incidented on it. Modules are formed by connecting number of individual solar cells, which are known as solar panels. In basic terms a single junction silicon solar cell can produce a maximum open-circuit voltage of approximately 0.5 to 0.6 volts.
Solar cells can be described as being photovoltaic, in spite of whether the source used is sunlight or an artificial light. They are used as a photodetector (for example infrared detectors), detecting light or other electromagnetic radiation near the visible range, or measuring light intensity.
The operation of a photovoltaic (PV) cell requires three basic imputes:
The absorption of light; here, either electron-hole pairs or excitons are produced.
The separation of charge carriers of opposite types.
The separate extraction of those carriers, then they are forwarded to an external circuit.
(A conventional crystalline silicon solar cell) (Thin film solar cell)
In opposition to a solar thermal collector supplies heat by absorbing sunlight, for the purpose of either direct heating or indirect electrical power generation from heat. On the other hand, a “photoelectrolytic cell” also known as photoelectrochemical cell, refers to either a type of photovoltaic cell (like that developed by Edmond Becquerel and modern dye-sensitized solar cells), or to a device which splits the water directly into hydrogen and oxygen using only solar radiance. Figure shows the typical solar cell made from Silicon (Si) which is crystalline and the symbol of a solar cell or a photovoltaic cell.
(Symbol of a Photovoltaic cell)
Types of solar cell and Material used to prepare Solar Cell
Solar cells are named after their basic material which is used to prepare it i.e. semiconducting material. These materials must have some certain characteristics for the purpose of absorption of the sunlight coming from the solar radiation. Solar cells can be fabricated from only one single layer of light-absorbing material, i.e. single-junction or by using multiple physical configurations (multi-junctions).
Solar cells can be divided into first, second and third generation cells. The first generation cells—also known as the conventional cells. They are prepared with the help of crystalline Silicon (Si), the commercially predominant PV technology, that includes materials such as polysilicon and monocrystalline silicon. Second generation cells are Thin film solar cells. In this type of solar cells, amorphous Silicon (Si), CdTe cells are used. The third generation of solar cells includes a number of thin-film technologies. Most of them have not been applied economically still and are yet under the RND phase. Many use organic materials, often organometallic compounds as well as inorganic substances. The stability of the absorber material was often too short for commercial applications, there is a lot of research invested into these technologies as they promise to achieve the goal of producing low-cost, high-efficiency solar cells.
The most popular bulk material for solar cells is crystalline silicon (c-Si), known as “solar grade silicon”. Bulk silicon is separated into multiple categories according to crystallinity and crystal size in the resulting ingot, ribbon or wafer. These cells are entirely based around the concept of a p-n junction. Solar cells made of c-Si are made from wafers between 160 and 240 micrometers thick.
Monocrystalline silicon (mono-Si) solar cells are more efficient and are higher in cost than other types of cells. The corners of the cells look clipped, like an octagon, because the wafer material is cut from cylindrical ingots. Solar panels using mono-Si cells display a distinctive pattern of small white diamonds.
Thin-film technologies reduce the amount of active material in a cell. Most designs sandwich active material between two panes of glass. Since silicon solar panels only use one pane of glass, thin film panels are approximately twice as heavy as crystalline silicon panels, although they have a smaller ecological impact (determined from life cycle analysis).
Cadmium telluride (CdTe)
Cadmium telluride is the only thin film material so far to rival crystalline silicon in cost/watt. However cadmium is highly toxic and tellurium’s anion-telluride supplies are limited. The cadmium present in the cells would be toxic if released. However, release is impossible during normal operation of the cells and is unlikely during fires in residential roofs. A square meter of CdTe contains approximately the same amount of Cd as a single C cell nickel-cadmium battery, in a more stable and less soluble form.
Silicon thin film
Silicon thin-film cells are mainly deposited by chemical vapor deposition (typically plasma-enhanced, PECVD) from silane gas and hydrogen gas. Depending on the deposition parameters, this can yield amorphous silicon (a-Si or a-Si:H), protocrystalline silicon or nanocrystalline silicon (nc-Si or nc-Si:H), also called microcrystalline silicon.
Amorphous silicon is the most well-developed thin film technology to-date. An amorphous silicon (a-Si) solar cell is made of non-crystalline or microcrystalline silicon. Amorphous silicon has a higher bandgap (1.7 eV) than crystalline silicon (c-Si) (1.1 eV), which means it absorbs the visible part of the solar spectrum more strongly than the higher power density infrared portion of the spectrum. The production of a-Si thin film solar cells uses glass as a substrate and deposits a very thin layer of silicon by plasma-enhanced chemical vapor deposition (PECVD).
Protocrystalline silicon with a low volume fraction of nanocrystalline silicon is optimal for high open circuit voltage.Nc-Si has about the same bandgap as c-Si and nc-Si and a-Si can advantageously be combined in thin layers, creating a layered cell called a tandem cell. The top cell in a-Si absorbs the visible light and leaves the infrared part of the spectrum for the bottom cell in nc-Si.
Gallium arsenide (GaAs) thin film
The semiconductor material Gallium arsenide (GaAs) is also used for single-crystalline thin film solar cells. Although GaAs cells are very expensive, they hold the world’s record in efficiency for a single-junction solar cell at 28.8%.61 GaAs is more commonly used in multijunction photovoltaic cells for concentrated photovoltaics (CPV, HCPV) and for solar panels on spacecrafts, as the industry favours efficiency over cost for space-based solar power.
Working of Solar Cell
The solar cell works in several steps:
Photons in sunlight are collisioned with the solar panel for the purpose of their absorption by the material used in solar cell e.g. semiconducting materials such as silicon (Si).
Electrons are excited from their current atomic orbit. These excited electrons can either dump the energy into heat and return to its orbit or travel through the cell until it reaches an electrode. Here, current flows through the material to abolish the potential and this electricity is generated. For this process to work, the chemical bonds of the material are important. Commonly Silicon (Si) is used in two layers; one layer is doped with boron and the other one is doped with Phosphorus (P). These layers have different chemical electric charges and afterwards, both drive and direct the current of electrons.
An array of solar cells converts solar energy coming from solar radiation into direct current (DC) electricity.
An inverter then used to convert the power to alternating current (AC).
(Working mechanism of a solar cell)
The well known and mostly now in use solar cell is constructed as a large-area p–n junction made from Silicon (Si) material. Other types of solar cell are perovskite solar cells, dye sensitized solar cells, quantum dot solar cells, organic solar cells etc. The illuminated side of a solar cell generally have a transparent conducting film for allowing light to enter into active material and to occupy the produced charge carriers. Typically, films with high transmittance and high electrical conductance such as Indium Tin oxide (ITO), conducting polymers or conducting Nano wire networks are used for the purpose.
CHAPTER 2: DSSC: DYE SENSITIZED SOLAR
What is DSSC?
In the late 1960s it was invented that illuminated organic dyes can produce electricity at oxide electrodes in electrochemical cells. The phenomenon was studied at the University of California at Berkeley with chlorophyll, which was extracted from spinach with a view to understand and simulate the primary processes in photosynthesis. On the back of these experiments, electric power generation via dye sensitized solar cell’s (DSSC) principle was determined and examined in 1972. The instability of the DSSC was scrutinized as a central challenge. Its efficiency could be improved by optimizing the porosity of the electrode prepared from fine oxide powder during the following two decades, but the instability remained a problem.
A modern DSSC consists of a porous layer of Titanium dioxide nanoparticles (TiO2 nps), enclosed with a molecular dye. This molecular dye is used to absorb the sunlight, just like the chlorophyll in green leaves of trees. Under an electrolyte solution, TiO2 is absorbed. One can add a platinum-based catalyst above this layer. In a conventional alkaline battery, an anode and a cathode are placed on either side of a liquid conductor (the electrolyte); we can have anode as titanium dioxide and cathode as platinum here.
Si gives two functions in traditional cell design, normally the silicon acts as both the source of photoelectrons, as well as providing the electric field to separate the charges and create a current. Dye-sensitized solar cells separate the two functions given by silicon in a typical cell design. In the dye-sensitized solar cell, the bulk of the semiconductor is used entirely for charge transport, the photoelectrons are provided from a separate photosensitive dye. Charge separation occurs at the surfaces between the dye, semiconductor and electrolyte.
The dye molecules are quite small i.e. nano sized, thus with a view to acquirement of a fair quantity of the incoming light, the layer of dye molecules require to be made thick enough, much thicker than the molecules themselves. A nano material is used as a scaffold to hold large numbers of the dye molecules in a 3-D matrix, increasing the number of molecules for any given surface area of cell to address this problem. In existing designs, this scaffolding is provided by the semiconductor material, which serves double-duty.
A dye-sensitized solar cell (DSSC, DSC, DYSC or Grätzel cell) is a not a high-cost solar cell because of the group of thin film solar cells. It is based on a semiconductor sandwiched between a photo-sensitized anode and an electrolyte, known as a photoelectrochemical system. The modern version of a dye solar cell is known as the Grätzel cell. It was originally invented in 1988 by Brian O’Regan and Michael Grätzel at UC Berkeley. This work was later developed by the aforementioned scientists at the École Polytechnique Fédérale de Lausanne until the publication of the first high efficiency DSSC in 1991. Michael Grätzel has been awarded the 2010 Millennium Technology Prize for this invention.
The DSSC has a lot of fair features; it is simple and easy to fabricate using conventional roll-printing techniques, for example semi-flexible and semi-transparent which offers a variety of uses not applicable to glass-based systems, and most of the materials used are low-cost. In practice it has proven difficult to remove a number of expensive materials, markedly platinum and ruthenium, and the liquid electrolyte presents a serious challenge to making a cell suitable for use in all weather. Commercial applications, which were held up due to chemical stability problems, are forecast in the European Union Photovoltaic Roadmap to significantly contribute to renewable electricitygeneration by 2020.
2. Construction: How it’s made?
When sunlight is passed through the transparent electrode into the dye layer where it can excite electrons that then flow into the layer of nanoparticles of TiO2. The electrons flow toward the transparent electrode. Here, they will be collected for powering a load. After flowing through the external circuit, these are introduced again back into the cell on a metal electrode on the back and then, they are flowed to the electrolyte. The electrolyte then transports the electrons to the dye molecules back.
In the case of the original Grätzel and O’Regan design, the cell has 3 primary parts. On top is a transparent anode made of fluoride-doped tin dioxide (SnO2:F) deposited on the back of a (typically glass) plate. On the back of this conductive plate is a thin layer of titanium dioxide (TiO2) to form a highly porous structure with an extremely high surface area. TiO2 is chemically bound by a process called sintering. TiO2 only absorbs a small fraction of the solar photons (those in the UV). The plate is then immersed in a mixture of a photosensitive ruthenium-polypyridine dye (also called molecular sensitizers) and a solvent. After soaking the film in the dye solution, a thin layer of the dye is left covalently bonded to the surface of the TiO2. The bond is an ester, chelating, or bidentate bridging linkage.
(Type of cell made at the EPFL by Grätzel and O’Regan)
A separate plate is then made with a thin layer of the iodide electrolyte spread over a conductive sheet, typically platinum metal. The two plates are then joined and sealed together to prevent the electrolyte from leaking. The construction is simple enough that there are hobby kits available to hand-construct them.Although they use a number of “advanced” materials, these are inexpensive compared to the silicon needed for normal cells because they require no expensive manufacturing steps. TiO2, for instance, is already widely used as a paint base.
One of the efficient DSSCs devices uses ruthenium-based molecular dye, e.g. Ru(4,4′-dicarboxy-2,2′-bipyridine)2(NCS)2 (N3), that is bound to a photoanode via carboxylate moieties. The photoanode consists of 12 ?m thick film of transparent 10–20 nm diameter TiO2 nanoparticles covered with a 4 ?m thick film of much larger (400 nm diameter) particles that scatter photons back into the transparent film. The excited dye rapidly injects an electron into the TiO2 after light absorption. The injected electron diffuses through the sintered particle network to be collected at the front side transparent conducting oxide (TCO) electrode, while the dye is regenerated via reduction by a redox shuttle, I3/I, dissolved in a solution. Diffusion of the oxidized form of the shuttle to the counter electrode completes the circuit.
Mechanism of DSSC: Construction
The following basic steps are required to convert photons i.e. light into current:
The incident photon is absorbed by Ru complex photosensitizers adsorbed on the TiO2 surface.
The photo sensitizers are excited from the ground state (S) to the excited state (S?). The excited electrons are injected into the conduction band of the TiO2 electrode. This results in the oxin of the photosensitizer (S+).
S + h? ? S*
S* S+ + e-
The injected electrons in the conduction band of TiO2 are transported between TiO2 nanoparticles with diffusion toward the back contact (TCO). And the electrons finally reach the counter electrode through the circuit.
The oxidized photosensitizer (S+) accepts electrons from the I? ion redox mediator leading to regeneration of the ground state (S), and two I?-Ions are oxidized to elementary Iodine which reacts with I? to the oxidized state, I3?.
S+ + e? ? S
The oxidized redox mediator, I3?, diffuses toward the counter electrode and then it is reduced to I? ions.
I3? + 2 e? ? 3 I?
(operation of Grätzel cell)
Sunlight enters the cell through the transparent SnO2: F top contact, striking the dye on the surface of the TiO2. Photons striking the dye with enough energy to be absorbed create an excited state of the dye, from which an electron can be “injected” directly into the conduction band of the TiO2. From there it moves by diffusion (as a result of an electron concentration gradient) to the clear anode on top.
Meanwhile, the dye molecule has lost an electron and the molecule will decompose if another electron is not provided. The dye strips one from iodide in electrolyte below the TiO2, oxidizing it into triiodide. This reaction occurs quite quickly compared to the time that it takes for the injected electron to recombine with the oxidized dye molecule, preventing this recombination reaction that would effectively short-circuit the solar cell.
The triiodide then recovers its missing electron by mechanically diffusing to the bottom of the cell, where the counter electrode re-introduces the electrons after flowing through the external circuit.
Chapter 3. Fabrication of DSSC
The transparent conductive indium doped tin oxide (ITO) coated glass (2 mm thickness of glass substrate with 8 ohm/sq. indium doped tin oxide coating on one side 5 × 5 cm2). TiCl4(98%), iodolyte AN-50 (iodide based low viscosity electrolyte with 50 mM of tri-iodide in acetonitrile), polyethylene glycol (99%), ethanol (99.9%), hydrochloric acid (HCl), copper plate as the counter electrode, and surfactant were used to fabricate dye-synthesized solar cells.
Synthesis of TiO2 and CuO nanoparticles
The nanoparticles of TiO2 were prepared via sol-gel method. Precursors used are TiCl4, polyethylene glycol (PEG) and distilled water. 10mL of TiCl4 was added in 50 mL of distilled water. Then, 20 mL of PEG was added to the mixture and distilled water to adjust the pH of solutions. The required precipitate was obtained by changing the final pH range of the solution from 2 to 6. The precipitate formed was washed, filtered and dried in an oven at 90°C for 24 h and calcined in the muffle furnace at 700°C for 2 h with a heating rate of 5°C/min. The synthesis of CuO nanoparticles with controllable sizes, forms with enhanced surface properties was reported by our group for solar energy collection. CuO nanoparticles with controlled sizes of ~5 nm were prepared using the most cost-effective sol-gel technique, where the solution was prepared using an acetate route with copper and its salt as starting materials, which were then dissolved in HCl acid and distilled water with ratio 1:1 and 0.6 molarity (M). The solution prepared above was stirred at 500 rpm and elevated temperature (~ 90°C) for 1 hour. Finally, the solution was heated at 90°C for 1 hour and 30 min to prepare the gel. The gel was calcined in the muffle furnace at 650°C for 3 h. Finally, the stoichiometry of TiO2:CuO was taken as 95:5 by weight and crushed in a porcelain mortar and a mallet with a few drops (~3 mL) of very dilute acetic acid (prepared by adding 0.2 mL of acetic acid concentrated to 100 mL of distilled water), 7 mL of ethanol and a few drops of nonionic surfactant were well mixed. The milling time was about half an hour to produce a homogeneous adhesive of titanium dioxide and copper oxide paste. In addition, the paste was aged for one day and coated with transparent conductive oxide (ITO) using a scraper blade method. After that, the slide was left for drying. While the electrode is heated to sinter the film at 450°C for 30 min, the last step of the preparation is that to allow the sheet to cool naturally at room temperature.
Preparation of natural dye sensitizers
The tomato contains anthocyanin pigment, which is red and has good adhesion with the layer of TiO2/CuO chosen as sensitizers. To extract this, rich tomatoes were taken and washed several times with water to remove all impurities. The cleaned tomato was crushed to make tomato paste. Then, 20 mL of ethanol is added to the tomato and refluxed for 90 min at 60°C. The resulting liquid was filtered off using filter paper and the dye extracted was stored for further usage. Finally, titanium dioxide and copper oxide nanoparticles were impregnated with tomato dye and kept for 10 h.
(Schematic representation of DSSC) (Dye sensitized solar cell)
The low-cost copper plate cathode has been an ideal material as the counter electrode. The active layer (titanium dioxide and copper oxide (95:5) wt% impregnated with natural dyes for 10 h is rinsed with absolute ethanol and dried with a hair dryer sandwiched between two electrodes, namely ITO and copper plate. The two electrodes were assembled using binders and sealed with a sealing frame. When the electrodes are sealed, two small holes keep left open to pore iodine electrolyte and finally sealed to prevent leakage. A schematic representation of the prepared DSSCs is shown in first figure above with necessary energy band representation and prepared cell is shown in second figure shown above.
Chapter 4. DESIGN ENGINEERING CANVAS
Canvas 1. AEIOU Summary:
This canvas includes main part of product. The starting part indicated environmental effect of DSSC. It uses sun light as input so it comes under the renewable source of energy. We also used natural dye which is non toxic to atmosphere so it can be said that it generated eco friendly electricity. To develop this kind of solar cell, we interacted with many people like researchers, students, faculties etc. We used sonicater and pistel-motor in preparation. Some other components are TiO2 nanoparticles, ITO glass, Liquid electrolyte etc. We also did activities:
Cleaning of ITO glass,
Checking of its conductivity,
Covering it with TiO2 nanoparticles and covering of this layer etc.
Canvas 2. Empathy mapping Canvas
Empathy mapping canvas indicates about the major user of this invention; e.g. general people. It also indicates the people connected with the major users which show the importance of this device in day to day life. The main use of solar cell is to charge some electrical appliances. It can also be used to run small devices of industries. After that, there is a story board which contains two happy and two sad stories wrote by us. It says about the advanced application of cell. Whereas sad story says about he disadvantages of this cell i.e. limitation; this cell is breakable as it contains the glass as electrodes. Another happy story says that use of this cell is eco friendly. While sad story is that it can not be used in the rainy season.
Canvas 3. Ideation Canvas
Ideation canvas may be helpful for the fabrication of DSSC: Dye sensitized solar cell in a convinient way to the fabricater. It contains the group of people using the solar cell and activities of solar cell i.e. process. Employed people with this cell are students, Scientists, Industrialists, Researcher etc. Another parrt includes the activities which are mentioned above in the canvas. It gives the possible applications of cell in various fields. The next part concentrates on the purpose of the cell and limitations of conventional cells. In conventional solar cells, some complex transformations are occurred while in this type of solar cell are eco friendly. Further, this canvas focusses on the properties of this solar cell. It is fabricated using eco friendly dye so it is non toxic. It also requires less area and less maintenance is required as compared to the others solar cells.
Canvas 4. Product Development canvas
This canvas is helpful to make product suitable for market. The purpose of this product is conveyed with the help of this canvas like to convert light energy into electrical energy efficiently and run solar cell with low maintenance. Some main functions of this type of cell are to transport electrical power, to absorb visible spectrum rays, to increase mean free path, applicable in too many appliances etc. This canvas also says about the feature of the product. It gives the reason to use Dye sensitized solar cell. The life time of such cell is almost same as compared to others. It also contains the components used.
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The summary comprises the advantages of Dye sensitized solar cell, fabrication and working of solar cell, scope of future work with its applications in various fields.
Advantages of Dye sensitized solar cell are;
Its cost effective production of solar cell
Eco friendly production
High chemical reactivity is achieved by high surface area.
Easy availability of materials to prepare the solar cell
We have modified the invention by its faults or defects i.e. some inabilities. The dye sensitized solar cell provides the remarkable values or makeable evolutions with less material usage and the ain thing to be noticed is that it is prepared with the help of natural dyes, which refers to the aim of eco-friendly production of green Nano technology.