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Flexible solar cell research is a research-level technology, an example of which was created at the Massachusetts Institute of Technology in which solar cells are manufactured by depositing photovoltaic material on flexible substrates, such as ordinary paper, using chemical vapor deposition technology. [1]
The technology for manufacturing solar cells on paper was developed by a group of researchers from the Massachusetts Institute of Technology with support from the National Science Foundation and the Eni-MIT Alliance Solar Frontiers Program.
Researchers at MIT developed a method for printing solar cells on fabrics or paper substrates. Circuits of organic photovoltaic materials are deposited in five layers on ordinary paper substrates in a vacuum chamber. It is done by coating conformal conductive polymer electrodes with oxidative chemical vapor, a process known as chemical vapor deposition. Such solar panels are capable of producing voltages exceeding than 50V, which in turn can power appliances at normal lighting conditions. The solar cell is also shown to be flexible. [2] The solar cell conductive grid is similar[ citation needed ] to an inkjet photo printout with patterned rectangles. When leads are attached to the electrical substrate, it is shown to power electrical appliances. The cost of "printing" (as MIT describes it) is claimed to be similar to that of inkjet photo printing. [3] This technology uses vapor deposition temperatures of less than 120°C, which makes it easier to manufacture on ordinary paper. [3] The current efficiency of the panel is near 1%, which the researcher hopes to improve in the near future. [3]
As paper costs approximately a thousandth of glass, solar cells using printing processes can be much cheaper than conventional solar panels. [3] Also other methods involving coating papers with materials include first coating the paper with a smooth material to counter-act the molecular scale roughness of paper. But in this method, the photovoltaic material can be coated directly onto untreated paper. [3]
The circuit was also tested by depositing the photovoltaic materials on a polyethylene terephthalate (PET) substrate. The PET sheet was folded and unfolded 1000 times and no overt deterioration in performance was observed,[ citation needed ] whereas common photovoltaic materials deposited on PET deteriorated with just a single fold.[ citation needed ] The solar cell was also passed through a laser printer to demonstrate its continued performance after exposure to [somewhat] high temperatures and it still retained its characteristics after the procedure. [3]
Crystalline silicon (c-Si) is an extremely popular semiconductor made into wafers, which are then used in the manufacturing of 95% of the world’s photovoltaics [4] . Due to its prevalence in the solar cell industry, it would appear to be an ideal substrate for flexible solar cells. Unfortunately, c-Si is brittle, and while some researchers have made solar cells from amorphous silicon that are flexible, these cells have some major drawbacks such as bad performance and unstable operating conditions [5] .
Recent research breakthroughs have yielded a method of engineering foldable c-Si wafers. The first step is saw-damage removal [6] , which uses an acidic solution to etch the surface of the wafers. This thins the wafers and textures the surface to form random pyramids, which increases flexibility and reduces the surface reflection of the normally glossy wafer, thereby increasing the efficiency of the solar cell. To minimize cracking, researchers have blunted the valleys between pyramids along the edges of the wafer with a hydrogen fluoride(HF) solution to round out the valleys and make them less sharp. Chemical vapor deposition was used to deposit layers of Si:H on both sides of the wafer, and circuitry was screen printed on the devices and glued down with silver paste. The sides of the cells that were expected to be exposed to sunlight coated with an anti-reflective layer to improve light-harvesting efficiency [7] .
When bending forces were applied to the textured wafer, both COMSOL simulations and in situ transmission electron microscopy(TEM) images showed that cracking began in the valleys between the pyramids. Upon blunting the valleys, a three-point bending test showed that the vertical displacement of the wafer was increased and the critical bending radius at the cracking moment decreased from approx 74%. This improvement in flexibility was verified by atomistic simulations, where an untreated wafer exhibited cracking under a 9.3% loading strain, and the treated wafers lasted until 17.3% [8] .
Closer analysis of the morphology of the blunted wafers using a stepwise focused ion beam(FIB) showed that the fracture surface had many cleavage sites and microcracks, which propagated down to a critical depth below the surface. Below this depth, secondary shear banding lines spread in tangential directions from the original cracks. These features show the complex stress state during the cracking process, wherein the initial cleaving consumed a greater amount of energy before visible cracks formed along the surface [9] .
TEM images of blunted and traditional wafers showed lattice strain features below the fracture surface. Lattice distortions caused the strains, meaning that residual features were preserved within the atomic layers and could be used as an indicator of the cracking mode. Geometric phase analysis [10] showed that normal wafers exhibited x-direction tensile strain and y-direction compressive and dilation strain, corresponding to typical brittle fracture. The blunted wafer had larger strain variations in both directions as well as larger dilation strain. Overall, these features show larger lattice expansion and that blunting the wafers mitigated the brittle characteristics of c-Si.
The flexible cell exhibited an efficiency of 24.5%. To test its performance, the cell was folded corner to corner 1,000 times and held for at least 10 seconds. After the cycles completed, 100% of the initial performance values were retained. Other tests include simulated wind blowing and extreme temperature exposure. In these tests the solar cells exhibited negligible power loss, showing that they could still work despite negative external factors [11] .
In conventional solar panels, the supporting structures of the panel like glass, brackets etc. are mostly twice as costly as the photovoltaic materials manufactured on them. Alternative solutions and creative solar cell substrates can mitigate these costs.
If such solar cells can achieve sufficient technological maturity, they can be used as wall paper and window shades for producing electricity from room lighting. They can also be manufactured on clothing, which can in turn be used to charge portable electronic devices like mobile phones and media players. [1]
Flexible solar modules can be used on curved roofs, or roofs where it does not make sense to install a rack mounting system. Additionally, they can be installed on walls of buildings to make solar a viable option in areas where land or rooftops are not able to have solar installed.
In order to last 20+ years outdoors exposed to the elements, such solar cells must be finished with a front sheet of a UV-resistant fluoropolymer or thermoplastic olefin rather than the glass used in conventional solar cells, which is comparatively inexpensive [ citation needed ]. Solar cells must be sealed so water and oxygen cannot enter and destroy the cells via oxidative degradation.
Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high-quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films.
Indium tin oxide (ITO) is a ternary composition of indium, tin and oxygen in varying proportions. Depending on the oxygen content, it can be described as either a ceramic or an alloy. Indium tin oxide is typically encountered as an oxygen-saturated composition with a formulation of 74% In, 8% Sn, and 18% O by weight. Oxygen-saturated compositions are so typical that unsaturated compositions are termed oxygen-deficient ITO. It is transparent and colorless in thin layers, while in bulk form it is yellowish to gray. In the infrared region of the spectrum it acts as a metal-like mirror.
A thin film is a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films is a fundamental step in many applications. A familiar example is the household mirror, which typically has a thin metal coating on the back of a sheet of glass to form a reflective interface. The process of silvering was once commonly used to produce mirrors, while more recently the metal layer is deposited using techniques such as sputtering. Advances in thin film deposition techniques during the 20th century have enabled a wide range of technological breakthroughs in areas such as magnetic recording media, electronic semiconductor devices, integrated passive devices, LEDs, optical coatings, hard coatings on cutting tools, and for both energy generation and storage. It is also being applied to pharmaceuticals, via thin-film drug delivery. A stack of thin films is called a multilayer.
An epitaxial wafer is a wafer of semiconducting material made by epitaxial growth (epitaxy) for use in photonics, microelectronics, spintronics, or photovoltaics. The epi layer may be the same material as the substrate, typically monocrystaline silicon, or it may be a silicon dioxide (SoI) or a more exotic material with specific desirable qualities. The purpose of epitaxy is to perfect the crystal structure over the bare substrate below and improve the wafer surface's electrical characteristics, making it suitable for highly complex microprocessors and memory devices.
A solar cell or photovoltaic cell is an electronic device that converts the energy of light directly into electricity by means of the photovoltaic effect. It is a form of photoelectric cell, a device whose electrical characteristics vary when it is exposed to light. Individual solar cell devices are often the electrical building blocks of photovoltaic modules, known colloquially as "solar panels". The common single-junction silicon solar cell can produce a maximum open-circuit voltage of approximately 0.5 to 0.6 volts.
On 8 September 2011 Nuon announced the pilot plant would be closed down since no investor for production expansion could be found. However, on 7 May 2012 Nuon announced that Helianthos has been sold to HyET Solar.
Printed electronics is a set of printing methods used to create electrical devices on various substrates. Printing typically uses common printing equipment suitable for defining patterns on material, such as screen printing, flexography, gravure, offset lithography, and inkjet. By electronic-industry standards, these are low-cost processes. Electrically functional electronic or optical inks are deposited on the substrate, creating active or passive devices, such as thin film transistors; capacitors; coils; resistors. Some researchers expect printed electronics to facilitate widespread, very low-cost, low-performance electronics for applications such as flexible displays, smart labels, decorative and animated posters, and active clothing that do not require high performance.
Ultrasonic nozzles are a type of spray nozzle that use high frequency vibrations produced by piezoelectric transducers acting upon the nozzle tip that create capillary waves in a liquid film. Once the amplitude of the capillary waves reaches a critical height, they become too tall to support themselves and tiny droplets fall off the tip of each wave resulting in atomization.
Monocrystalline silicon, more often called single-crystal silicon, in short mono c-Si or mono-Si, is the base material for silicon-based discrete components and integrated circuits used in virtually all modern electronic equipment. Mono-Si also serves as a photovoltaic, light-absorbing material in the manufacture of solar cells.
Thin-film solar cells are made by depositing one or more thin layers of photovoltaic material onto a substrate, such as glass, plastic or metal. Thin-film solar cells are typically a few nanometers (nm) to a few microns (µm) thick–much thinner than the wafers used in conventional crystalline silicon (c-Si) based solar cells, which can be up to 200 µm thick. Thin-film solar cells are commercially used in several technologies, including cadmium telluride (CdTe), copper indium gallium diselenide (CIGS), and amorphous thin-film silicon.
A copper indium gallium selenide solar cell is a thin-film solar cell used to convert sunlight into electric power. It is manufactured by depositing a thin layer of copper indium gallium selenide solid solution on glass or plastic backing, along with electrodes on the front and back to collect current. Because the material has a high absorption coefficient and strongly absorbs sunlight, a much thinner film is required than of other semiconductor materials.
A plasmonic-enhanced solar cell, commonly referred to simply as plasmonic solar cell, is a type of solar cell that converts light into electricity with the assistance of plasmons, but where the photovoltaic effect occurs in another material.
Crystalline silicon or (c-Si) Is the crystalline forms of silicon, either polycrystalline silicon, or monocrystalline silicon. Crystalline silicon is the dominant semiconducting material used in photovoltaic technology for the production of solar cells. These cells are assembled into solar panels as part of a photovoltaic system to generate solar power from sunlight.
Ultra-high-purity steam, also called the clean steam, UHP steam or high purity water vapor, is used in a variety of industrial manufacturing processes that require oxidation or annealing. These processes include the growth of oxide layers on silicon wafers for the semiconductor industry, originally described by the Deal-Grove model, and for the formation of passivation layers used to improve the light capture ability of crystalline photovoltaic cells. Several methods and technologies can be employed to generate ultra high purity steam, including pyrolysis, bubbling, direct liquid injection, and purified steam generation. The level of purity, or the relative lack of contamination, affects the quality of the oxide layer or annealed surface. The method of delivery affects growth rate, uniformity, and electrical performance. Oxidation and annealing are common steps in the manufacture of such devices as microelectronics and solar cells.
There are currently many research groups active in the field of photovoltaics in universities and research institutions around the world. This research can be categorized into three areas: making current technology solar cells cheaper and/or more efficient to effectively compete with other energy sources; developing new technologies based on new solar cell architectural designs; and developing new materials to serve as more efficient energy converters from light energy into electric current or light absorbers and charge carriers.
Polycrystalline silicon, or multicrystalline silicon, also called polysilicon, poly-Si, or mc-Si, is a high purity, polycrystalline form of silicon, used as a raw material by the solar photovoltaic and electronics industry.
Inkjet solar cells are solar cells manufactured by low-cost, high tech methods that use an inkjet printer to lay down the semiconductor material and the electrodes onto a solar cell substrate.
A perovskite solar cell (PSC) is a type of solar cell that includes a perovskite-structured compound, most commonly a hybrid organic–inorganic lead or tin halide-based material as the light-harvesting active layer. Perovskite materials, such as methylammonium lead halides and all-inorganic cesium lead halide, are cheap to produce and simple to manufacture.
Amorphous silicon (a-Si) is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCDs.
Heterojunction solar cells (HJT), variously known as Silicon heterojunctions (SHJ) or Heterojunction with Intrinsic Thin Layer (HIT), are a family of photovoltaic cell technologies based on a heterojunction formed between semiconductors with dissimilar band gaps. They are a hybrid technology, combining aspects of conventional crystalline solar cells with thin-film solar cells.
