A thin-film solar cell is a second generation
solar cell
A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. that is made by depositing one or more thin layers, or
thin film
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 (a process referred to as deposition) is a fundamental step in many ap ...
(TF) of
photovoltaic
Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially us ...
material on a substrate, such as glass, plastic or metal. Thin-film solar cells are commercially used in several technologies, including
cadmium telluride
Cadmium telluride (CdTe) is a stable crystalline compound formed from cadmium and tellurium. It is mainly used as the semiconducting material in cadmium telluride photovoltaics and an infrared optical window. It is usually sandwiched with ca ...
(CdTe),
copper indium gallium diselenide
Copper indium gallium (di)selenide (CIGS) is a I- III- VI2 semiconductor material composed of copper, indium, gallium, and selenium. The material is a solid solution of copper indium selenide (often abbreviated "CIS") and copper gallium selenide ...
(CIGS), and
amorphous thin-film silicon (a-Si, TF-Si).
Film thickness varies from a few nanometers (
nm) to tens of micrometers (
µm), much thinner than thin-film's rival technology, the conventional, first-generation
crystalline silicon
Crystalline silicon or (c-Si) Is the crystalline forms of silicon, either polycrystalline silicon (poly-Si, consisting of small crystals), or monocrystalline silicon (mono-Si, a continuous crystal). Crystalline silicon is the dominant semicondu ...
solar cell (c-Si), that uses
wafers
A wafer is a crisp, often sweet, very thin, flat, light and dry biscuit, often used to decorate ice cream, and also used as a garnish on some sweet dishes. Wafers can also be made into cookies with cream flavoring sandwiched between them. They ...
of up to 200 µm thick. This allows thin film cells to be flexible, and lower in weight. It is used in
building-integrated photovoltaics
Building-integrated photovoltaics (BIPV) are photovoltaic materials that are used to replace conventional building materials in parts of the building envelope such as the roof, skylights, or facades. They are increasingly being incorporated in ...
and as semi-
transparent
Transparency, transparence or transparent most often refer to:
* Transparency (optics), the physical property of allowing the transmission of light through a material
They may also refer to:
Literal uses
* Transparency (photography), a still, ...
, photovoltaic glazing material that can be
laminated
Lamination is the technique/process of manufacturing a material in multiple layers, so that the composite material achieves improved strength, stability, sound insulation, appearance, or other properties from the use of the differing materia ...
onto windows. Other commercial applications use rigid thin film
solar panel
A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a photo ...
s (interleaved between two panes of glass) in some of the
world's largest photovoltaic power stations
A photovoltaic power station, also known as a solar park, solar farm, or solar power plant, is a large-scale grid-connected photovoltaic power system (PV system) designed for the supply of merchant power. They are different from most building- ...
.
Thin-film technology has always been cheaper but less efficient than conventional c-Si technology. However, it has significantly improved over the years. The lab cell efficiency for CdTe and CIGS is now beyond 21 percent, outperforming
multicrystalline silicon, the dominant material currently used in most
solar PV systems
A photovoltaic system, also PV system or solar power system, is an electric power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and co ...
.
Accelerated life testing Accelerated life testing is the process of testing a product by subjecting it to conditions (stress, strain, temperatures, voltage, vibration rate, pressure etc.) in excess of its normal service parameters in an effort to uncover faults and potenti ...
of thin film modules under laboratory conditions measured a somewhat faster degradation compared to conventional PV, while a lifetime of 20 years or more is generally expected. Despite these enhancements, the market-share of thin-film never reached more than 20 percent in the last two decades and has been declining in recent years to about 9 percent of
worldwide photovoltaic installations in 2013.
Other thin-film technologies that are still in an early stage of ongoing research or with limited commercial availability are often classified as emerging or
third generation photovoltaic cell
Third-generation photovoltaic cells are solar cells that are potentially able to overcome the Shockley–Queisser limit of 31–41% power efficiency for single bandgap solar cells. This includes a range of alternatives to cells made of semiconduc ...
s and include
organic,
dye-sensitized, as well as
quantum dot
Quantum dots (QDs) are semiconductor particles a few nanometres in size, having light, optical and electronics, electronic properties that differ from those of larger particles as a result of quantum mechanics. They are a central topic in nanote ...
,
copper zinc tin sulfide
Copper zinc tin sulfide (CZTS) is a quaternary semiconducting compound which has received increasing interest since the late 2000s for applications in thin film solar cells. The class of related materials includes other I2-II-IV-VI4 such as copp ...
,
nanocrystal
A ''nanocrystal'' is a material particle having at least one dimension smaller than 100 nanometres, based on quantum dots
(a nanoparticle) and composed of atoms in either a single- or poly-crystalline arrangement.
The size of nanocrystals dist ...
,
micromorph The portmanteau micromorph is a combination of the words microcrystalline and amorphous. It is used for a type of silicon based multijunction thin-film solar cell.
The micromorph cell
Micromorph cells are thin film solar cells based on a mult ...
, and
perovskite solar cell
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 a ...
s.
History
![Global photovoltaics market share by technology 1980-2021](https://upload.wikimedia.org/wikipedia/commons/1/1b/Global_photovoltaics_market_share_by_technology_1980-2021.svg)
Thin film cells are well-known since the late 1970s, when
solar calculators powered by a small strip of amorphous silicon appeared on the market.
They are now available in very large modules used in sophisticated
building-integrated installations and
vehicle charging systems.
Although thin-film technology was expected to make significant advances in the market and to surpass the dominating conventional
crystalline silicon
Crystalline silicon or (c-Si) Is the crystalline forms of silicon, either polycrystalline silicon (poly-Si, consisting of small crystals), or monocrystalline silicon (mono-Si, a continuous crystal). Crystalline silicon is the dominant semicondu ...
(c-Si) technology in the long-term, market-share has been declining for several years now. While in 2010, when there was a shortage of conventional PV modules, thin-film accounted for 15 percent of the overall market, it declined to 8 percent in 2014, and is expected to stabilize at 7 percent from 2015 onward, with amorphous silicon expected to lose half of its market-share by the end of the decade.
Materials
![Illust poly thinfilm](https://upload.wikimedia.org/wikipedia/commons/e/e8/Illust_poly_thinfilm.gif)
Thin-film technologies reduce the amount of active material in a cell. Most 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
Life cycle assessment or LCA (also known as life cycle analysis) is a methodology for assessing environmental impacts associated with all the stages of the life cycle of a commercial product, process, or service. For instance, in the case ...
). The majority of film panels have 2-3 percentage points lower conversion efficiencies than crystalline silicon.
Cadmium telluride
Cadmium telluride (CdTe) is a stable crystalline compound formed from cadmium and tellurium. It is mainly used as the semiconducting material in cadmium telluride photovoltaics and an infrared optical window. It is usually sandwiched with ca ...
(CdTe),
copper indium gallium selenide
Copper indium gallium (di)selenide (CIGS) is a I-III- VI2 semiconductor material composed of copper, indium, gallium, and selenium. The material is a solid solution of copper indium selenide (often abbreviated "CIS") and copper gallium selenide. ...
(CIGS) and
amorphous silicon
Amorphous silicon (a-Si) is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCDs.
Used as semiconductor material for a-Si solar cells, or thin-film silicon solar cells, it is deposited in thin films ont ...
(a-Si) are three thin-film technologies often used for outdoor applications.
Cadmium telluride
Cadmium telluride
Cadmium telluride (CdTe) is a stable crystalline compound formed from cadmium and tellurium. It is mainly used as the semiconducting material in cadmium telluride photovoltaics and an infrared optical window. It is usually sandwiched with ca ...
(CdTe) is the predominant thin film technology. With about 5 percent of worldwide PV production, it accounts for more than half of the thin film market. The cell's lab efficiency has also increased significantly in recent years and is on a par with CIGS thin film and close to the efficiency of multi-crystalline silicon as of 2013.
Also, CdTe has the lowest
Energy payback time of all mass-produced PV technologies, and can be as short as eight months in favorable locations.
A prominent manufacturer is the US-company
First Solar
First Solar, Inc. is an American manufacturer of solar panels, and a provider of utility-scale PV power plants and supporting services that include finance, construction, maintenance and end-of-life panel recycling. First Solar uses rigid thi ...
based in
Tempe, Arizona
, settlement_type = City
, named_for = Vale of Tempe
, image_skyline = Tempeskyline3.jpg
, imagesize = 260px
, image_caption = Tempe skyline as se ...
, that produces CdTe-panels with an efficiency of about 18 percent.
Although the toxicity of
cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of ...
may not be that much of an issue and environmental concerns completely resolved with the recycling of CdTe modules at the end of their life time,
[
] there are still uncertainties and the public opinion is skeptical towards this technology. The usage of rare materials may also become a limiting factor to the industrial scalability of CdTe thin film technology. The rarity of
tellurium
Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally fou ...
—of which telluride is the
anion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
ic form—is comparable to that of platinum in the earth's crust and contributes significantly to the module's cost.
Copper indium gallium selenide
A copper indium gallium selenide solar cell or
CIGS cell
A copper indium gallium selenide solar cell (or CIGS cell, sometimes CI(G)S or CIS 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 soluti ...
uses an absorber made of
copper, indium, gallium, selenide (CIGS), while gallium-free variants of the semiconductor material are abbreviated CIS. It is one of three mainstream thin-film technologies, the other two being
cadmium telluride
Cadmium telluride (CdTe) is a stable crystalline compound formed from cadmium and tellurium. It is mainly used as the semiconducting material in cadmium telluride photovoltaics and an infrared optical window. It is usually sandwiched with ca ...
and
amorphous silicon
Amorphous silicon (a-Si) is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCDs.
Used as semiconductor material for a-Si solar cells, or thin-film silicon solar cells, it is deposited in thin films ont ...
, with a lab-efficiency above 20 percent and a share of 2 percent in the overall PV market in 2013. A prominent manufacturer of cylindrical CIGS-panels was the now-bankrupt company
Solyndra
Solyndra was a manufacturer of cylindrical panels of copper indium gallium selenide (CIGS) thin film solar cells based in Fremont, California. Heavily promoted as a leader in the sustainable energy sector for its unusual technology, Solyndra wa ...
in Fremont, California. Traditional methods of fabrication involve vacuum processes including co-evaporation and sputtering. In 2008,
IBM and Tokyo Ohka Kogyo Co., Ltd. (TOK) announced they had developed a new, non-vacuum, solution-based manufacturing process for CIGS cells and are aiming for efficiencies of 15% and beyond.
Hyperspectral imaging
Hyperspectral imaging collects and processes information from across the electromagnetic spectrum. The goal of hyperspectral imaging is to obtain the spectrum for each pixel in the image of a scene, with the purpose of finding objects, identifyi ...
has been used to characterize these cells. Researchers from IRDEP (Institute of Research and Development in Photovoltaic Energy) in collaboration with
Photon etc.¸ were able to determine the splitting of the quasi-Fermi level with
photoluminescence
Photoluminescence (abbreviated as PL) is light emission from any form of matter after the absorption of photons (electromagnetic radiation). It is one of many forms of luminescence (light emission) and is initiated by photoexcitation (i.e. photon ...
mapping while the
electroluminescence
Electroluminescence (EL) is an optical phenomenon, optical and electrical phenomenon, in which a material emits light in response to the passage of an electric current or to a strong electric field. This is distinct from black body light emissi ...
data were used to derive the
external quantum efficiency
The term quantum efficiency (QE) may apply to incident photon to converted electron (IPCE) ratio of a photosensitive device, or it may refer to the TMR effect of a Magnetic Tunnel Junction.
This article deals with the term as a measurement of ...
(EQE). Also, through a light beam induced current (LBIC) cartography experiment, the EQE of a microcrystalline CIGS solar cell could be determined at any point in the field of view.
As of April 2019, current conversion efficiency record for a laboratory CIGS cell stands at 22.9%.
Silicon
Three major silicon-based module designs dominate:
* amorphous silicon cells
* amorphous / microcrystalline tandem cells (micromorph)
* thin-film polycrystalline silicon on glass.
[.]
Amorphous silicon
Amorphous silicon
Amorphous silicon (a-Si) is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCDs.
Used as semiconductor material for a-Si solar cells, or thin-film silicon solar cells, it is deposited in thin films ont ...
(a-Si) is a non-crystalline, allotropic form of silicon and the most well-developed thin film technology to-date. Thin-film silicon is an alternative to conventional ''
wafer
A wafer is a crisp, often sweet, very thin, flat, light and dry biscuit, often used to decorate ice cream, and also used as a garnish on some sweet dishes. Wafers can also be made into cookies with cream flavoring sandwiched between them. They ...
'' (or ''bulk'')
crystalline silicon
Crystalline silicon or (c-Si) Is the crystalline forms of silicon, either polycrystalline silicon (poly-Si, consisting of small crystals), or monocrystalline silicon (mono-Si, a continuous crystal). Crystalline silicon is the dominant semicondu ...
. While
chalcogen
The chalcogens (ore forming) ( ) are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioact ...
ide-based CdTe and CIS thin films cells have been developed in the lab with great success, there is still industry interest in silicon-based thin film cells. Silicon-based devices exhibit fewer problems than their CdTe and CIS counterparts such as toxicity and humidity issues with CdTe cells and low manufacturing yields of CIS due to material complexity. Additionally, due to political resistance to the use non-"green" materials in solar energy production, there is no stigma in the use of standard silicon.
![Aerospace Product-Flexible Thin-Film Solar PV-United Solar Ovonic](https://upload.wikimedia.org/wikipedia/commons/5/50/Aerospace_Product-Flexible_Thin-Film_Solar_PV-United_Solar_Ovonic.jpg)
This type of thin-film cell is mostly fabricated by a technique called
plasma-enhanced chemical vapor deposition
Plasma-enhanced chemical vapor deposition (PECVD) is a chemical vapor deposition process used to deposit thin films from a gas state (vapor) to a solid state on a substrate. Chemical reactions are involved in the process, which occur after creati ...
. It uses a gaseous mixture of
silane
Silane is an inorganic compound with chemical formula, . It is a colourless, pyrophoric, toxic gas with a sharp, repulsive smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon. Sila ...
(SiH
4) and hydrogen to deposit a very thin layer of only 1 micrometre (µm) of silicon on a substrate, such as glass, plastic or metal, that has already been coated with a layer of
transparent conducting oxide
Transparent conducting films (TCFs) are thin films of optically transparent and electrically conductive material. They are an important component in a number of electronic devices including liquid-crystal displays, OLEDs, touchscreens and phot ...
. Other methods used to deposit amorphous silicon on a substrate include
sputtering
In physics, sputtering is a phenomenon in which microscopic particles of a solid material are ejected from its surface, after the material is itself bombarded by energetic particles of a plasma or gas. It occurs naturally in outer space, and ca ...
and hot wire
chemical vapor deposition
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.
In typical CVD, the wafer (substra ...
techniques.
[Photovoltaics]
Engineering.Com (July 9, 2007). Retrieved on January 19, 2011.
a-Si is attractive as a solar cell material because it's an abundant, non-toxic material. It requires a low processing temperature and enables a scalable production upon a flexible, low-cost substrate with little silicon material required. Due to its bandgap of 1.7 eV, amorphous silicon also absorbs a very broad range of the
light spectrum
The electromagnetic spectrum is the range of frequency, frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energy, photon energies.
The electromagnetic spectrum covers electromagnetic waves with f ...
, that includes
infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
and even some
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
and performs very well at weak light. This allows the cell to generate power in the early morning, or late afternoon and on cloudy and rainy days, contrary to
crystalline silicon
Crystalline silicon or (c-Si) Is the crystalline forms of silicon, either polycrystalline silicon (poly-Si, consisting of small crystals), or monocrystalline silicon (mono-Si, a continuous crystal). Crystalline silicon is the dominant semicondu ...
cells, that are significantly less efficient when exposed at
diffuse
Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...
and indirect
daylight
Daylight is the combination of all direct and indirect sunlight during the daytime. This includes direct sunlight, diffuse sky radiation, and (often) both of these reflected by Earth and terrestrial objects, like landforms and buildings. Sunligh ...
.
However, the efficiency of an a-Si cell suffers a significant drop of about 10 to 30 percent during the first six months of operation. This is called the
Staebler-Wronski effect (SWE) – a typical loss in electrical output due to changes in photoconductivity and dark conductivity caused by prolonged exposure to sunlight. Although this degradation is perfectly reversible upon
annealing at or above 150 °C, conventional c-Si solar cells do not exhibit this effect in the first place.
Its basic electronic structure is the
p-i-n junction. The amorphous structure of a-Si implies high inherent disorder and dangling bonds, making it a bad conductor for charge carriers. These dangling bonds act as recombination centers that severely reduce carrier lifetime. A p-i-n structure is usually used, as opposed to an n-i-p structure. This is because the mobility of electrons in a-Si:H is roughly 1 or 2 orders of magnitude larger than that of holes, and thus the collection rate of electrons moving from the n- to p-type contact is better than holes moving from p- to n-type contact. Therefore, the p-type layer should be placed at the top where the light intensity is stronger, so that the majority of the charge carriers crossing the junction are electrons.
Tandem-cell using a-Si/μc-Si
A layer of amorphous silicon can be combined with layers of other allotropic forms of silicon to produce a
multi-junction solar cell Multi-junction (MJ) solar cells are solar cells with multiple p–n junctions made of different semiconductor materials. Each material's p-n junction will produce electric current in response to different wavelengths of light. The use of multiple ...
. When only two layers (two p-n junctions) are combined, it is called a ''tandem-cell''. By stacking these layers on top of one other, a broader range of the light spectra is absorbed, improving the cell's overall efficiency.
In
micromorph The portmanteau micromorph is a combination of the words microcrystalline and amorphous. It is used for a type of silicon based multijunction thin-film solar cell.
The micromorph cell
Micromorph cells are thin film solar cells based on a mult ...
ous silicon, a layer of
microcrystalline silicon
Nanocrystalline silicon (nc-Si), sometimes also known as microcrystalline silicon (μc-Si), is a form of porous silicon. It is an allotropic form of silicon with paracrystalline structure—is similar to amorphous silicon (a-Si), in that it has ...
(μc-Si) is combined with amorphous silicon, creating a tandem cell. The top a-Si layer absorbs the visible light, leaving the infrared part to the bottom μc-Si layer. The micromorph stacked-cell concept was pioneered and patented at the Institute of Microtechnology (IMT) of the Neuchâtel University in Switzerland, and was licensed to
TEL Solar. A new world record PV module based on the
micromorph The portmanteau micromorph is a combination of the words microcrystalline and amorphous. It is used for a type of silicon based multijunction thin-film solar cell.
The micromorph cell
Micromorph cells are thin film solar cells based on a mult ...
concept with 12.24% module efficiency was independently certified in July 2014.
Because all layers are made of silicon, they can be manufactured using PECVD. The
band gap
In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in ...
of a-Si is 1.7 eV and that of c-Si is 1.1 eV. The c-Si layer can absorb red and infrared light. The best efficiency can be achieved at transition between a-Si and c-Si. As nanocrystalline silicon (nc-Si) has about the same bandgap as c-Si, nc-Si can replace c-Si.
Tandem-cell using a-Si/pc-Si
Amorphous silicon can also be combined with
protocrystalline
A protocrystalline phase is a distinct phase occurring during crystal growth which evolves into a microcrystalline form. The term is typically associated with silicon films in optical applications such as solar cells.
Applications
Silicon sol ...
silicon (pc-Si) into a tandem-cell. Protocrystalline silicon with a low volume fraction of nanocrystalline silicon is optimal for high
open-circuit voltage
Open-circuit voltage (abbreviated as OCV or VOC) is the difference of electrical potential between two terminals of an electronic device when disconnected from any circuit. There is no external load connected. No external electric current f ...
. These types of silicon present dangling and twisted bonds, which results in deep defects (energy levels in the bandgap) as well as deformation of the
valence and
conduction band
In solid-state physics, the valence band and conduction band are the bands closest to the Fermi level, and thus determine the electrical conductivity of the solid. In nonmetals, the valence band is the highest range of electron energies in w ...
s (band tails).
Polycrystalline silicon on glass
A new attempt to fuse the advantages of bulk silicon with those of thin-film devices is thin film polycrystalline silicon on glass. These modules are produced by depositing an antireflection coating and doped silicon onto textured glass substrates using plasma-enhanced chemical vapor deposition (PECVD). The texture in the glass enhances the efficiency of the cell by approximately 3% by reducing the amount of incident light reflecting from the solar cell and trapping light inside the solar cell. The silicon film is crystallized by an annealing step, temperatures of 400–600 Celsius, resulting in polycrystalline silicon.
These new devices show energy conversion efficiencies of 8% and high manufacturing yields of >90%. Crystalline silicon on glass (CSG), where the polycrystalline silicon is 1–2 micrometres, is noted for its stability and durability; the use of thin film techniques also contributes to a cost savings over bulk photovoltaics. These modules do not require the presence of a transparent conducting oxide layer. This simplifies the production process twofold; not only can this step be skipped, but the absence of this layer makes the process of constructing a contact scheme much simpler. Both of these simplifications further reduce the cost of production. Despite the numerous advantages over alternative design, production cost estimations on a per unit area basis show that these devices are comparable in cost to single-junction amorphous thin film cells.
Gallium arsenide
Gallium arsenide
Gallium arsenide (GaAs) is a III-V direct band gap semiconductor with a Zincblende (crystal structure), zinc blende crystal structure.
Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monoli ...
(GaAs) is a III-V direct bandgap semiconductor and is a very common material used for single-crystalline thin-film solar cells. GaAs solar cells have continued to be one of the highest performing thin-film solar cells due to their exceptional heat resistant properties and high efficiencies. As of 2019, single-crystalline GaAs cells have shown the highest solar cell efficiency of any single-junction solar cell with an efficiency of 29.1%. This record-holding cell achieved this high efficiency by implementing a back mirror on the rear surface to increase photon absorption which allowed the cell to attain an impressive short-circuit current density and an
open-circuit voltage
Open-circuit voltage (abbreviated as OCV or VOC) is the difference of electrical potential between two terminals of an electronic device when disconnected from any circuit. There is no external load connected. No external electric current f ...
value near the
Shockley–Queisser limit
In physics, the radiative efficiency limit (also known as the detailed balance limit, Shockley–Queisser limit, Shockley Queisser Efficiency Limit or SQ Limit) is the maximum theoretical efficiency of a solar cell using a single p-n junction ...
. As a result, GaAs solar cells have nearly reached their maximum efficiency although improvements can still be made by employing light trapping strategies.
GaAs thin-films are most commonly fabricated using
epitaxial
Epitaxy refers to a type of crystal growth or material deposition in which new crystalline layers are formed with one or more well-defined orientations with respect to the crystalline seed layer. The deposited crystalline film is called an epit ...
growth of the semiconductor on a substrate material. The epitaxial lift-off (ELO) technique, first demonstrated in 1978, has proven to be the most promising and effective. In this method, the thin film layer is peeled off of the substrate by selectively etching a sacrificial layer that was placed between the epitaxial film and substrate. The GaAs film and the substrate remain minimally damaged through the separation process, allowing for the reuse of the host substrate. With reuse of the substrate the fabrication costs can be reduced, but not completely forgone, since the substrate can only be reused a limited number of times.
This process is still relatively costly and research is still being done to find more cost-effective ways of growing the epitaxial film layer onto a substrate.
Despite the high performance of GaAs thin-film cells, the expensive material costs hinder their ability for wide-scale adoption in the solar cell industry. GaAs is more commonly used in
multi-junction solar cell Multi-junction (MJ) solar cells are solar cells with multiple p–n junctions made of different semiconductor materials. Each material's p-n junction will produce electric current in response to different wavelengths of light. The use of multiple ...
s for
solar panels on spacecraft
Spacecraft operating in the inner Solar System usually rely on the use of power electronics-managed photovoltaic solar panels to derive electricity from sunlight. Outside the orbit of Jupiter, solar radiation is too weak to produce sufficient pow ...
, as the larger power to weight ratio lowers the launch costs in
space-based solar power (
InGaP
Indium gallium phosphide (InGaP), also called gallium indium phosphide (GaInP), is a semiconductor composed of indium, gallium and phosphorus. It is used in high-power and high-frequency electronics because of its superior electron velocity with ...
/
(In)GaAs/
Ge cells). They are also used in
concentrator photovoltaics
Concentrator photovoltaics (CPV) (also known as concentration photovoltaics) is a photovoltaic technology that generates electricity from sunlight. Unlike conventional photovoltaic systems, it uses lenses or curved mirrors to focus sunlight onto ...
, an emerging technology best suited for locations that receive much sunlight, using lenses to focus sunlight on a much smaller, thus less expensive GaAs concentrator solar cell.
Emerging photovoltaics
![Glitter-Sized Solar Cells (8230058366)](https://upload.wikimedia.org/wikipedia/commons/f/fc/Glitter-Sized_Solar_Cells_%288230058366%29.jpg)
The
National Renewable Energy Laboratory
The National Renewable Energy Laboratory (NREL) in the US specializes in the research and development of renewable energy, energy efficiency, energy systems integration, and sustainable transportation. NREL is a federally funded research and d ...
classifies a number of thin-film technologies as emerging photovoltaics—most of them have not yet been commercially applied and are still in the research or development phase. Many use organic materials, often
organometallic
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...
compounds as well as inorganic substances. Despite the fact that their efficiencies had been low and 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-efficient solar cells.
Emerging photovoltaics, often called
third generation photovoltaic cell
Third-generation photovoltaic cells are solar cells that are potentially able to overcome the Shockley–Queisser limit of 31–41% power efficiency for single bandgap solar cells. This includes a range of alternatives to cells made of semiconduc ...
s, include:
*
Copper zinc tin sulfide
Copper zinc tin sulfide (CZTS) is a quaternary semiconducting compound which has received increasing interest since the late 2000s for applications in thin film solar cells. The class of related materials includes other I2-II-IV-VI4 such as copp ...
solar cell (CZTS), and derivates CZTSe and CZTSSe
*
Dye-sensitized solar cell, also known as "Grätzel cell"
*
Organic solar cell
An organic solar cell (OSC) or plastic solar cell is a type of photovoltaic that uses organic electronics, a branch of electronics that deals with conductive organic polymers or small organic molecules, for light absorption and charge transport t ...
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Perovskite solar cell
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 a ...
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Quantum dot solar cell
A quantum dot solar cell (QDSC) is a solar cell design that uses quantum dots as the absorbing photovoltaic material. It attempts to replace bulk materials such as silicon, copper indium gallium selenide ( CIGS) or cadmium telluride ( CdTe). Qua ...
Perovskite solar cells
![Perovskite solar cells 1](https://upload.wikimedia.org/wikipedia/commons/d/dc/Perovskite_solar_cells_1.jpg)
Especially the achievements in the research of perovskite cells have received tremendous attention in the public, as their research efficiencies recently soared above 20 percent. They also offer a wide spectrum of low-cost applications. In addition, another emerging technology,
concentrator photovoltaics
Concentrator photovoltaics (CPV) (also known as concentration photovoltaics) is a photovoltaic technology that generates electricity from sunlight. Unlike conventional photovoltaic systems, it uses lenses or curved mirrors to focus sunlight onto ...
(CPV), uses high-efficient,
multi-junction solar cell Multi-junction (MJ) solar cells are solar cells with multiple p–n junctions made of different semiconductor materials. Each material's p-n junction will produce electric current in response to different wavelengths of light. The use of multiple ...
s in combination with optical lenses and a tracking system.
Transparent solar cells
In 2022, semitransparent solar cells that are as large as windows were reported, after team members of the study achieved record efficiency with high transparency in 2020. Also in 2022, other researchers reported the fabrication of solar cells with a record average visible transparency of 79%, being nearly invisible.
Efficiencies
The achievable efficiency of thin-film solar cells is extremely dependent on the semiconductor chosen and the growth technology. Incremental improvements in efficiency began with the invention of the first modern silicon solar cell in 1954. By 2010 these steady improvements had resulted in modules capable of converting 12 to 18 percent of solar radiation into electricity. The improvements to efficiency have continued to accelerate in the years since 2010, as shown in the accompanying chart.
Cells made from newer materials tend to be less efficient than bulk silicon, but are less expensive to produce. Their
quantum efficiency
The term quantum efficiency (QE) may apply to incident photon to converted electron (IPCE) ratio of a photosensitive device, or it may refer to the TMR effect of a Magnetic Tunnel Junction.
This article deals with the term as a measurement of ...
is also lower due to reduced number of collected
charge carrier
In physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. The term is used ...
s per incident photon.
The performance and potential of thin-film materials are high, reaching
cell
Cell most often refers to:
* Cell (biology), the functional basic unit of life
Cell may also refer to:
Locations
* Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...
efficiencies of 12–20%;
prototype
A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and Software prototyping, software programming. A prototyp ...
module efficiencies of 7–13%; and production
module
Module, modular and modularity may refer to the concept of modularity. They may also refer to:
Computing and engineering
* Modular design, the engineering discipline of designing complex devices using separately designed sub-components
* Mo ...
s in the range of 9%.
[Utility-Scale Thin-Film: Three New Plants in Germany Total Almost 50 MW]
/ref>
The thin film cell prototype with the best efficiency yields 20.4% (First Solar), comparable to the best conventional solar cell prototype efficiency of 25.6% from Panasonic
formerly between 1935 and 2008 and the first incarnation of between 2008 and 2022, is a major Japanese multinational corporation, multinational Conglomerate (company), conglomerate corporation, headquartered in Kadoma, Osaka, Kadoma, Osaka P ...
.
NREL
The National Renewable Energy Laboratory (NREL) in the US specializes in the research and development of renewable energy, energy efficiency, energy systems integration, and sustainable transportation. NREL is a federally funded research and d ...
once predicted that costs would drop below $100/m2 in volume production, and could later fall below $50/m2.
A new record for thin film solar cell efficiency of 22.3% has been achieved by Solar Frontier
Solar Frontier Kabushiki Kaisha is a Japanese photovoltaic company that develops and manufactures thin film solar cells using Copper indium gallium selenide solar cells, CIGS technology. It is a fully owned subsidiary of Showa Shell Sekiyu and loc ...
, the world's largest CIS (copper indium selenium) solar energy provider. In joint research with the New Energy and Industrial Technology Development Organization
The , or NEDO, is Japan's largest public management organization promoting research and development as well as deployment of industrial, energy and environmental technologies. In 2003, NEDO was reorganized as an Independent Administrative Institu ...
(NEDO) of Japan, Solar Frontier achieved 22.3% conversion efficiency on a 0.5 cm2 cell using its CIS technology. This is an increase of 0.6 percentage points over the industry's previous thin-film record of 21.7%.
Absorption
Multiple techniques have been employed to increase the amount of light that enters the cell and reduce the amount that escapes without absorption. The most obvious technique is to minimize the top contact coverage of the cell surface, reducing the area that blocks light from reaching the cell.
The weakly absorbed long wavelength light can be obliquely coupled into silicon and traverses the film several times to enhance absorption.
Multiple methods have been developed to increase absorption by reducing the number of incident photons being reflected away from the cell surface. An additional anti-reflective coating can cause destructive interference within the cell by modulating the refractive index
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
The refractive index determines how much the path of light is bent, or ...
of the surface coating. Destructive interference eliminates the reflective wave, causing all incident light to enter the cell.
Surface texturing is another option for increasing absorption, but increases costs. By applying a texture to the active material's surface, the reflected light can be refracted into striking the surface again, thus reducing reflectance. For example, black silicon texturing by reactive ion etching(RIE) is an effective and economic approach to increase the absorption of thin-film silicon solar cells. A textured backreflector can prevent light from escaping through the rear of the cell.
In addition to surface texturing, the plasmonic light-trapping scheme attracted a lot of attention to aid photocurrent enhancement in thin film solar cells. This method makes use of collective oscillation of excited free electrons in noble metal nanoparticles, which are influenced by particle shape, size and dielectric properties of the surrounding medium.
In addition to minimizing reflective loss, the solar cell material itself can be optimized to have higher chance of absorbing a photon that reaches it. Thermal processing techniques can significantly enhance the crystal quality of silicon cells and thereby increase efficiency. Layering thin-film cells to create a multi-junction solar cell Multi-junction (MJ) solar cells are solar cells with multiple p–n junctions made of different semiconductor materials. Each material's p-n junction will produce electric current in response to different wavelengths of light. The use of multiple ...
can also be done. Each layer's band gap can be designed to best absorb a different range of wavelengths, such that together they can absorb a greater spectrum of light.
Further advancement into geometric considerations can exploit nanomaterial dimensionality. Large, parallel nanowire arrays enable long absorption lengths along the length of the wire while maintaining short minority carrier diffusion lengths along the radial direction. Adding nanoparticles between the nanowires allows conduction. The natural geometry of these arrays forms a textured surface that traps more light.
Production, cost and market
With the advances in conventional crystalline silicon
Crystalline silicon or (c-Si) Is the crystalline forms of silicon, either polycrystalline silicon (poly-Si, consisting of small crystals), or monocrystalline silicon (mono-Si, a continuous crystal). Crystalline silicon is the dominant semicondu ...
(c-Si) technology in recent years, and the falling cost of the polysilicon
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.
Polysilicon is produce ...
feedstock, that followed after a period of severe global shortage, pressure increased on manufacturers of commercial thin-film technologies, including amorphous thin-film silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium diselenide (CIGS), leading to the bankruptcy of several companies. As of 2013, thin-film manufacturers continue to face price competition from Chinese refiners of silicon and manufacturers of conventional c-Si solar panels. Some companies together with their patents were sold to Chinese firms below cost.
Market-share
In 2013 thin-film technologies accounted for about 9 percent of worldwide deployment, while 91 percent was held by crystalline silicon ( mono-Si and multi-Si). With 5 percent of the overall market, CdTe holds more than half of the thin-film market, leaving 2 percent to each CIGS and amorphous silicon.
CIGS technology
:Several prominent manufacturers couldn't stand the pressure caused by advances in conventional c-Si technology of recent years. The company Solyndra
Solyndra was a manufacturer of cylindrical panels of copper indium gallium selenide (CIGS) thin film solar cells based in Fremont, California. Heavily promoted as a leader in the sustainable energy sector for its unusual technology, Solyndra wa ...
ceased all business activity and filed for Chapter 11 bankruptcy in 2011, and Nanosolar
Nanosolar was a developer of solar power technology. Based in San Jose, CA, Nanosolar developed and briefly commercialized a low-cost printable solar cell manufacturing process. The company started selling thin-film CIGS panels mid-December 20 ...
, also a CIGS manufacturer, closed its doors in 2013. Although both companies produced CIGS solar cells, it has been pointed out, that the failure was not due to the technology but rather because of the companies themselves, using a flawed architecture, such as, for example, Solyndra's cylindrical substrates.[
] In 2014, Korean LG Electronics
LG Electronics Inc. () is a South Korean multinational electronics company headquartered in Yeouido-dong, Seoul, South Korea. LG Electronics is a part of LG Corporation, the fourth largest '' chaebol'' in South Korea, and often considered a ...
terminated research on CIGS restructuring its solar business, and Samsung SDI
Samsung SDI Co., Ltd. () is a battery and electronic materials manufacturer headquartered in Yongin, Gyeonggi-do, South Korea. Samsung SDI operates its business with Energy Solutions and Electronic Materials segment. The Energy Solution segment ma ...
decided to cease CIGS-production, while Chinese PV manufacturer Hanergy
Hanergy Holding Group Ltd. (Hanergy) is a Chinese multinational company headquartered in Beijing. The company is focusing on thin-film solar value chain, including manufacturing and solar parks development. It also owns the Jinanqiao Hydroelectri ...
is expected to ramp up production capacity of their 15.5% efficient, 650 mm×1650 mm CIGS-modules. One of the largest producers of CI(G)S photovoltaics is the Japanese company Solar Frontier
Solar Frontier Kabushiki Kaisha is a Japanese photovoltaic company that develops and manufactures thin film solar cells using Copper indium gallium selenide solar cells, CIGS technology. It is a fully owned subsidiary of Showa Shell Sekiyu and loc ...
with a manufacturing capacity in the gigawatt-scale. ''(Also see List of CIGS companies
This list of notable companies manufacturing copper indium gallium selenide solar cells (CIGS) includes a number of companies, some of which have significantly reduced or completely closed down production:
* Ascent Solar Technologies
* Avancis ...
)''.
CdTe technology
:The company First Solar
First Solar, Inc. is an American manufacturer of solar panels, and a provider of utility-scale PV power plants and supporting services that include finance, construction, maintenance and end-of-life panel recycling. First Solar uses rigid thi ...
, a leading manufacturer of CdTe, has been building several of the world's largest solar power stations, such as the Desert Sunlight Solar Farm
The Desert Sunlight Solar Farm is a 550 megawatt (MW AC) photovoltaic power station approximately six miles north of Desert Center, California, United States, in the Mojave Desert. It uses approximately 8.8 million cadmium telluride modul ...
and Topaz Solar Farm
Topaz Solar Farm is a 550 megawatt ( MWAC) photovoltaic power station in San Luis Obispo County, California, United States. Construction on the project began in November 2011 and ended in November 2014. It is one of the world's largest sola ...
, both in the Californian desert with a 550 MW capacity each, as well as the 102-megawatt Nyngan Solar Plant in Australia, the largest PV power station in the Southern Hemisphere, commissioned in 2015.
:In 2011, GE announced plans to spend $600 million on a new CdTe solar cell plant and enter this market, and in 2013, First Solar bought GE's CdTe thin-film intellectual property portfolio and formed a business partnership. In 2012 Abound Solar, a manufacturer of cadmium telluride modules, went bankrupt.
a-Si technology
:In 2012, ECD solar, once one of the world's leading manufacturer of amorphous silicon (a-Si) technology, filed for bankruptcy in Michigan, United States. Swiss OC Oerlikon
OC Oerlikon is a listed technology group headquartered in Pfäffikon ( Schwyz), Switzerland. The name "Oerlikon" (or "œrlikon", as the company styles itself according to its corporate identity) comes from the Oerlikon district in Zurich where ...
divested its solar division that produced a-Si/μc-Si tandem cells to Tokyo Electron Limited.
:Other companies that left the amorphous silicon thin-film market include DuPont
DuPont de Nemours, Inc., commonly shortened to DuPont, is an American multinational chemical company first formed in 1802 by French-American chemist and industrialist Éleuthère Irénée du Pont de Nemours. The company played a major role in ...
, BP, Flexcell, Inventux, Pramac, Schuco, Sencera, EPV Solar, NovaSolar (formerly OptiSolar) and Suntech Power
Suntech Power Holdings Co., Ltd. () is a Chinese producer of solar panels, with of annual production capacity by the end of 2011. It is headquartered in Wuxi, Jiangsu. Shunfeng International Clean Energy Limited, a HKSE listed renewable energy inv ...
that stopped manufacturing a-Si modules in 2010 to focus on conventional silicon solar panels. In 2013, Suntech filed for bankruptcy in China.[
] In August 2013, the spot market price of thin-film a-Si and a-Si/µ-Si dropped to €0.36 and €0.46, respectively (about $0.50 and $0.60) per watt.
See also
* List of photovoltaics companies
This is a list of notable photovoltaics (PV) companies.
Grid-connected solar photovoltaics (PV) is the fastest growing energy technology in the world, growing from a cumulative installed capacity of 7.7 GW in 2007, to 320 GW in 2016. In 2016 ...
* Plasmonic solar cell
A plasmonic-enhanced solar cell, commonly referred to simply as plasmonic solar cell, is a type of solar cell (including thin-film, crystalline silicon, amorphous silicon, and other types of cells) that converts light into electricity with the assi ...
References
Sources
*Grama, S. "A Survey of Thin-Film Solar Photovoltaic Industry & Technologies." Massachusetts Institute of Technology, 2008.
* Green, Martin A. "Consolidation of thin-film photovoltaic technology: the coming decade of opportunity.” Progress in Photovoltaics: Research and Applications 14, no. 5 (2006): 383–392.
*Green, M. A. “Recent developments in photovoltaics.” Solar Energy 76, no. 1-3 (2004): 3–8.
*Beaucarne, Guy. “Silicon Thin-Film Solar Cells.” Advances in OptoElectronics 2007 (August 2007): 12.
*Ullal, H. S., and B. von Roedern. “Thin Film CIGS and CdTe Photovoltaic Technologies: Commercialization, Critical Issues, and Applications; Preprint” (2007).
*Hegedus, S. “Thin film solar modules: the low cost, high throughput and versatile alternative to Si wafers.” Progress in Photovoltaics: Research and Applications 14, no. 5 (2006): 393–411.
*Poortmans, J., and V. Arkhipov. Thin Film Solar Cells: Fabrication, Characterization and Applications. Wiley, 2006.
*Wronski, C.R., B. Von Roedern, and A. Kolodziej. “Thin-film Si:H-based solar cells.” Vacuum 82, no. 10 (June 3, 2008): 1145–1150.
*Chopra, K. L., P. D. Paulson, and V. Dutta. “Thin-film solar cells: an overview.” Progress in Photovoltaics: Research and Applications 12, no. 2-3 (2004): 69–92.
*Hamakawa, Y. Thin-Film Solar Cells: Next Generation Photovoltaics and Its Applications. Springer, 2004.
*Green, Martin. “Thin-film solar cells: review of materials, technologies and commercial status.” Journal of Materials Science: Materials in Electronics 18 (October 1, 2007): 15–19.
External links
Solar Panels
Link Solar
Flexcellence
a STReP financed by the Sixth Framework Programme
The Framework Programmes for Research and Technological Development, also called Framework Programmes or abbreviated FP1 to FP9, are funding programmes created by the European Union/European Commission to support and foster research in the Europe ...
(FP6) of the EU. Full title : Roll-to-roll
In the field of electronic devices, roll-to-roll processing, also known as web processing, reel-to-reel processing or R2R, is the process of creating electronic devices on a roll of flexible plastic, metal foil, or flexible glass. In other fields p ...
technology for the production of high-efficiency low cost thin-film silicon photovoltaic modules.
{{Photovoltaics