Background
Photovoltaics (PV) is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material. Materials presently used for photovoltaics include monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium gallium selenide/sulfide. The study of these material in terms of their availability, abundance, efficiency, lifetime usage, doping density, energy produced per gram, cost and several other parameters will help us in future to determine which materials would be the best to use in solar cells. Photovoltaics
Overview articles[edit | edit source]
Abundance of materials in the lithosphere[1][edit | edit source]
This ref shows the percentage of materials available to us in the form of raw material in the earth's crust.
- Silicon, 270,000 ppm
- Gallium, 19 ppm
- Indium, 0.160 ppm
- Tellurium, 0.001 ppm
Mineral availability[2][edit | edit source]
1. Tellurium Primary and intermediate producers further refined domestic and imported commercial-grade metal and tellurium dioxide, producing tellurium and tellurium compounds in high-purity form for specialty applications. Tellurium was increasingly used in the production of cadmium-tellurium-based solar cells and was the major end use for tellurium. It states that the world refinery production and reserves for Telluirium was 24,000 metric tons in 2012. But The figures shown for reserves include only tellurium contained in copper reserves. These estimates assume that more than one-half of the tellurium contained in unrefined copper anodes was actually recovered.
2. Indium Indium's abundance in the continental crust is estimated to be approximately 0.05 part per million. Trace amounts of indium occur in base metal sulfides—particularly chalcopyrite, sphalerite, and stannite—by ionic substitution. Indium is most commonly recovered from the zinc-sulfide ore mineral sphalerite. The average indium content of zinc deposits from which it is recovered ranges from less than 1 part per million to 100 parts per million. Although the geochemical properties of indium are such that it occurs with other base metals—copper, lead, and tin— and to a lesser extent with bismuth, cadmium, and silver, most deposits of these metals are subeconomic for indium. The world refinery production for Indium was 670 metric tons in 2012.
3. Gallium The average content of gallium in bauxite is 50 parts per million (ppm). U.S. bauxite deposits consist mainly of subeconomic resources that are not generally suitable for alumina production owing to their high silica content. Recovery of gallium from these deposits is therefore unlikely. Some domestic zinc ores contain as much as 50 ppm gallium and, as such, could be a significant resource. World resources of gallium in bauxite are estimated to exceed 1 billion kilograms, and a considerable quantity could be present in world zinc reserves. The foregoing estimate applies to total gallium content; only a small percentage of this metal in bauxite and zinc ores is economically recoverable. World primary gallium production capacity in 2012 was estimated to be 474 tons; refinery capacity, 270 tons; and recycling capacity, 198 tons.
Materials Availability Expands the Opportunity for Large-Scale Photovoltaics Deployment[3][edit | edit source]
Solar photovoltaics have great promise for a low-carbon future but remain expensive relative to other technologies. This paper has examined 23 promising semiconducting materials. Twelve composite materials systems were found to have the capacity to meet or exceed the annual worldwide electricity consumption of 17 000 TWh, of which nine have the potential for a significant cost reduction over crystalline silicon. They found that devices performing below 10%power conversion efficiencies deliver the same life time energy output as those above 20% when a 3/4 material reduction is achieved. By one recent estimate, the U.S. could achieve 69% of electricity and 35% of total energy consumption by 2050 entirely with existing PV technologies but may require almost half a trillion dollars in subsidies.
Today, modules represent ∼54% of the total installed cost for existing PV technologies, notably mono- and polycrystalline silicon, where silicon processing is estimated to be ∼85% of the energy input of the finished module (10–13). Aggressive development of nonsilicon-based PV materials has changed the PV landscape, offering exciting near-term cost reductions for material systems like copper indium gallium selenide (CIGS) and cadmium telluride (CdTe). the average quality of copper ore has gone from 2.4% to 1% in the last 100 years. The fraction of recoverable zinc that has already been placed in use is 19%, and indium, a secondary metal byproduct of zinc mining, has seen its price increase 400% in the past five years due to an increase in demand from the digital display market. One such hypothetical analysis demonstrated that a CdTe device with a cell thickness of 2 µm and operating at 10% power conversion efficiency was found to be capable of producing 0.3 TW per year before material scarcity was to become a limiting factor. Total annual electricity potential P in terawatt hours (TWh) is calculated by the following equation:
P=I·η·A·C·H/beta·10^12 where I is the solar spectrum intensity taken as a global air mass index (AM1.5G) of 1000 W/m2, A is the annual production per mineral in metric tons, C is the capacity factor for operation taken at 20%, and H is the number of hours per year.
Solar cell efficiency tables (version 42)[4][edit | edit source]
This paper consolidates the information in tables showing the highest independently confirmed efficiencies for solar cells and modules. The first new result in Table I is a very recent result, the demonstration of 19.6% efficiency for a 1-cm2 CdTe cell fabricated by GE Global Research and measured by the Newport Technology and Application Center. This is a significant improvement upon the previous best efficiency of 18.3% for a CdTe cell of this size. The second new cell result in Table I is an improvement in the performance of a 1-cm2 nanocrystalline silicon solar cell to 10.7%. A third new result in Table I is an improvement in efficiency to 8.2% for a 25-cm2 organic cell submodule fabricated by Toshiba and measured by the Japanese National Institute of Advanced Industrial Science and Technology (AIST). A third new result in Table I is an improvement in efficiency to 8.2% for a 25-cm2 organic cell submodule fabricated by Toshiba and measured by the Japanese National Institute of Advanced Industrial Science and Technology (AIST).
The first new result in Table II is a new record for a large area silicon module. An efficiency of 22.4% is reported for a 1.6-m2 silicon module fabricated by SunPower and measured by NREL. The second new result reported in Table II is a record for any polycrystalline thin-film module, with 16.1% total area efficiency reported for a 0.72-m2 CdTe module fabricated by First Solar [10] and again measured at NREL.
The first new result in table III is a new efficiency record for a large-area silicon cell with 24.7% efficiency reported for a 102-cm2 HIT cell (Heterojunction with Intrinsic Thin-layer cell) fabricated on an n-type silicon wafer substrate by Panasonic and measured by AIST. The second new result in Table III is 20.8% efficiency for a small area (0.25 cm2) crystalline GaInP cell fabricated and measured by NREL. The third new result is 20.4% efficiency for a small area (0.52 cm2) flexible CIGS cell developed by EMPA, the Swiss Federal Laboratory for Materials Science and Technology, and measured at FhG-ISE.
Table IV reports one new result for concentrator cells. A new record of 44.4% for the conversion of sunlight by any means is reported for a 0.165-cm2 multijunction cell operating at a concentration of 302 suns (direct irradiance of 302 kW/m2). The cell is an InGaP/GaAs/InGaAs triple junction device fabricated by Sharp and measured at FhG-ISE.
Silicon[5][edit | edit source]
Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure free element in nature. It is most widely distributed in dusts, sands, planetoids, and planets as various forms of silicon dioxide (silica) or silicates. Over 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the Earth's crust (about 28% by mass) after oxygen. Elemental silicon also has a large impact on the modern world economy. Although most free silicon is used in the steel refining, aluminum-casting, and fine chemical industries, the relatively small portion of very highly purified silicon that is used in semiconductor electronics (< 10%) is perhaps even more critical. Because of wide use of silicon in integrated circuits, the basis of most computers, a great deal of modern technology depends on it. Metallurgical grade silicon is commercially prepared by the reaction of high-purity silica with wood, charcoal, and coal in an electric arc furnace using carbon electrodes. At temperatures over 1,900 °C (3,450 °F), the carbon in the aforementioned materials and the silicon undergo the chemical reaction SiO2 + 2 C → Si + 2 CO. Liquid silicon collects in the bottom of the furnace, which is then drained and cooled. The silicon produced in this manner is called metallurgical grade silicon and is at least 98% pure. As of September 2008, metallurgical grade silicon costs about US$1.45 per pound ($3.20/kg), up from $0.77 per pound ($1.70/kg) in 2005. Solar grade silicon cannot be used for semiconductors, where purity must be extreme to properly control the process. Bulk silicon wafers used at the beginning of the integrated circuit making process must first be refined to "nine nines" purity (99.9999999%), a process which requires repeated applications of refining technology. The majority of electronic grade silicon crystals grown for device production are produced by the Czochralski process, (CZ-Si) since it is the cheapest method available and it is capable of producing large size crystals.
Twenty‐four percent efficient silicon solar cells with double layer antireflection coatings and reduced resistance loss[6][edit | edit source]
This paper report the increase in the cell efficiency by a combination of several mechanisms. One is the reduction of recombination at cell surfaces using atomic hydrogen passivation of silicon/silicon dioxide interfaces. Joule resistive losses in the cell have been reduced by a process which allows different thickness for fine and coarse features in the top cell metallization. Finally, reflection losses have been reduced by the use of a double layer antireflection coating. It gives the fabrication details that was used to generate the cells. They have stressed on the SiO2 layer to be as thin as possible so as to keep the recombination losses in oxide covered area to be low. Metal contact to the cell rear is made through small holes in this oxide (10micron X 10micron) to keep the contact area as small as possible due to the inferior recombination properties of this region. Immediately beneath these rear contact areas, the silicon is heavily doped (with boron) to further suppress contact recombination by sup-pressing minority carrier concentrations. For the present de-vices, the top surface contact was made via a contact stripe through the oxide of 2micron width, slightly narrower than in earlier devices to further reduce the recombination loss at this contact.
19.8% efficient "honeycomb" textured multicrystalline and 24.4% monocrystalline silicon solar cells[7][edit | edit source]
in this paper a substantially improved efficiency for a multicrystalline silicon solar cell of 19.8% is reported together with an incremental improvement in monocrystalline cell efficiency to 24.4%. The improved multicrystalline cell performance results from enshrouding cell surfaces in thermally grown oxide to reduce their detrimental electronic activity and from isotropic etching to form an hexagonally symmetric honeycomb surface texture. This texture reduces reflection loss as well as substantially increasing the cell's effective optical thickness by causing light to be trapped within the cell by total internal reflection.
The 1.5 V cm multicrystalline material used in this work was prepared using a modified directional solidification approach,4 sawn into wafers and processed into cells of 260 micron thickness with the structure shown in Fig. 1. An important feature is the use of thin, thermally grown silicon dioxide layers to almost completely enshroud the cell. This oxide reduces recombination along cell surfaces, improving both the collection probability for carriers photogenerated near the surface and the cell open-circuit voltage. The inverted-pyramid surface texturing used in monocrystalline PERL cells is not suited to multicrystalline substrates since it relies on anisotropic etching to expose intersecting {111} crystal planes forming pyramid sides.Such texturing not only reduces front surface reflection but increases the cell's effective optical thickness. Weakly ab-sorbed light is reflected from the cell's rear and strikes the top surface texture internally. Experimentally, the inverted-pyramid structure has been the most effective in trapping this light by total internal reflection, increasing the cell's effec-tive optical thickness by factors as high as 40. It has shown that the monocrystalline silicon cells using inverted pyramids have incresed the efficiency from 24% to 24.4%. The lower reflection from the tex-tured samples results from increased absorption in this rear reflector due to multiple light passes across the cell. The results suggest light trapping in the honeycomb textured cell is comparably effective to that in inverted-pyramid cells.
24.5% Eciency Silicon PERT Cells on MCZ Substrates and 24.7% Eciency PERL Cells on FZ Substrates[8][edit | edit source]
This model showed the highest efficiency achieved with crystalline silicon solar cells. They were able to achieve 24.7% using passivated emitter. rear locally diffused (PERL) structure. The major advantage of the PERL cells is passivation of most of the cell surface areas with high quality TCA(trichloroethane) grown SiO2. Both front and rear metal contact areas are also passivated by heavily phosphorus and boron diffused regions. The inverted pyramid front surface and the rear surface mirror form an excellent light trapping scheme. Hence, the PERL cells give very high open-circuit voltage and short-circuit current density on FZ substrates with high post-processing minority carrier lifetimes. The PERL cell metallisation pattern has also been recently re-optimised to further reduce the metallisation shading and resistance losses.
Polycrystalline silicon[9][edit | edit source]
Polycrystalline and paracrystalline phases are composed of a number of smaller crystals or crystallites. Polycrystalline silicon is a material consisting of multiple small silicon crystals. Polycrystalline cells can be recognized by a visible grain, a "metal flake effect". Semiconductor grade (also solar grade) polycrystalline silicon is converted to "single crystal" silicon ie the randomly associated crystallites of silicon in "polycrystalline silicon" are converted to a large "single" crystal. Single crystal silicon is used to manufacture most Si-based microelectronic devices. Polycrystalline silicon can be as much as 99.9999% pure. Ultra-pure poly is used in the semiconductor industry, starting from poly rods that are two to three meters in length. One major difference between polysilicon and a-Si is that the mobility of the charge carriers of the polysilicon can be orders of magnitude larger and the material also shows greater stability under electric field and light-induced stress. This allows more complex, high-speed circuity to be created on the glass substrate along with the a-Si devices, which are still needed for their low-leakage characteristics. When polysilicon and a-Si devices are used in the same process this is called hybrid processing. Upgraded metallurgical-grade (UMG) silicon (also known as UMG-Si) solar cell is being produced as a low cost alternative to polysilicon created by the Siemens process. UMG greatly reduces impurities in a variety of ways that require less equipment and energy than the Siemens process. UMG is about 99% pure which is three or more orders of magnitude less pure and about 10 times less expensive than polysilicon ($1.70 to $3.20 per kg from 2005 to 2008 compared to $40 to $400 per kg for polysilicon). It has the potential to provide nearly-as-good solar cell efficiency at 1/5 the capital expenditure, half the energy requirements, and less than $15/kg. At $50/kg and 7.5 g/W, module manufacturers spend $0.37/W for the polysilicon.
Cadmium telluride photovoltaics[10][edit | edit source]
Cadmium telluride has a bandgap of 1.5 eV and CdTe PV is the only thin film photovoltaic technology to surpass crystalline silicon PV in cheapness for a significant portion of the PV market, namely in multi-kilowatt systems. CdTe PV is considered the ecologically leading technology as it provides a solution to key ecological issues including climate change, energy security, and water scarcity. On a life cycle basis, CdTe PV has the smallest carbon footprint, lowest water use, and fastest energy payback time of all solar technologies. CdTe cell efficiency is approaching 20% in the laboratory with a world record of 19.6% as of 2013. There has been a lot of research on fabricating CdTe cells on flexible substrate since 1999. In 2009, EMPA, the Swiss Federal Laboratories for Materials Testing and Research, demonstrated a 12.4% efficient solar cell on flexible polyimide substrate. Recently, First Solar, Inc. and GE/Primestar have made a series of advances in research cell efficiencies with the most recent record being made in 2013 at 19.6%. In 2013, the record module efficiency was 16.1%. First Solar's record-breaking module efficiency marks a substantial increase from the 14.4% record of the previous year.[36] These achievements demonstrate that CdTe's efficiency potential is far from saturated.
Cadmium flows and emissions from CdTe PV: future expectations[11][edit | edit source]
From the abstract of this paper we get to know of the future prospects of CdTe thin film technology by stating that it already represents the largest contributor to non-silicon based photovoltaics worldwide. On the basis of the finding done, they found out that while CdTe PV may account for a large percentage of future global Cd demand, its role in terms of Cd sequestration may be beneficial. They also calculated that its potential contribution to yearly global Cd emissions to air and water may well be orders-of-magnitude lower than the respective current Cd emissions rates in Europe. It states that the global demand for primary cadmium was approximately 0.6% in 2008 while its market share is expanding very rapidly, already representing 5% of the total market for photovoltaics (EPIA and Greenpeace, 2008), with a single producer now supporting a production capacity of 1.1 GW/year (First Solar, 2009a). It talks about the certain assumptions it made to conclude with a take which gave them the required information for a future of cadmium use till 2050.
Cadmium is an extremely toxic material and it occurs in small amounts in zinc ores, so that Zn producers do not have the option of not mining Cd. Zn extraction and processing have grown for the last three decades, from approximately 5.5 million tonnes per year in the early 1970s to about 11 million tonnes per year today (USGS, 2009a and USGS, 2009b). In contrast, total (primary+secondary) Cd demand expanded much more slowly in the 1970s and '80s, and since remained virtually stable at roughly 20,000 tonnes/year (USGS, 2009a and USGS, 2009c). In fact, since the global production of Zn has increased much faster than the corresponding demand for Cd, the annual amounts of raw Cd generated are entirely determined by Zn production rates. In their analysis thay calculated that the global potential production of primary Cd from processing Zn ores was approximately 33,000 tonnes per year, based on an average Cd/Zn ratio in the ores of 0.003 (UNEP, 2006). Based on the information taken from the research groups in Europe they have also stated the cadmium emission that occur due to combustion of fossil fuels in coal- and oil-fired power plants and boilers, accounting for over 60% of the total. The average Cd content in coal reportedly ranges from 0.1 g/tonne (Pacyna and Pacyna, 2001) to 3 g/tonne (Swaine, 1995); petroleum oil has a comparatively lower Cd content, ranging 0.002–0.2 g/tonne (Karlsson et al., 2004). Other important sources of atmospheric Cd emissions are from producing and recycling galvanized iron and steel, as well as the life cycle of non-ferrous metal industrial products containing Zn, together adding up to approximately 15% of the total emissions. A third relevant source is the cement sector, contributing over 10% of the total. The metal industry account for 71 % od Cd emission into the water and in soil, The sedimentary phosphate rocks from which virtually all the commercial phosphate is produced naturally contain cadmium in concentrations from about 15 to over 200 mg (Cd)/kg (P2O5) (EC, 2001 and Oosterhuis et al., 2000).
The Impact of Tellurium Supply on Cadmium Telluride Photovoltaics[12][edit | edit source]
CdTe sales are growing rapidly, but there is concern about projecting hundredfold increases in power production relative to current production with CdTe PV modules. One reason is that Te, a humble nonmetal that is actually abundant in the universe, is as rare as many of the precious metals recovered from Earth's crust. CdTe module production costs have dropped from over $2/W in 2004 to $0.84/W in 2010, the lowest in photovoltaics (2). A key advantage of CdTe for thin-film devices is that it can be deposited rapidly.
Any favorable projections for CdTe PV will be moot if its contribution to power production is severely limited by Te supply. For the present technology, generating 1 gigawatt (GW) of power requires 91,000 kg (91 metric tons, MT) of Te (a cost of about $20 million). If all of the PV delivered in 2009—7 GW—had been produced with CdTe, about 640 MT of Te would have been required, which is comparable to its present annual production.
If PV is to supply 10% of the projected demand of electricity worldwide in 2030, the per annum growth rate must be 18.5%; for 25% of world electricity, it must be 25%. In 2030, the annual production would require 200 GW/year (at 10% electricity supply) or 670 GW/year (at 25% supply). For the current CdTe modules, 19,000 or 61250 MT of Te per year, respectively, would be needed, equivalent to an increase in supply by a factor of about 40 to more than 100, respectively.
The crustal abundance of Te is similar to that of platinum, but the actual recovery of Te is more than twice that of platinum. This paper gives the analysis to reduce the CdTe thickness which will ultimately reduce the use of tellurium use and the cost associated with it.
Future recycling flows of tellurium from cadmium telluride photovoltaic waste[13][edit | edit source]
According to the European Photovoltaic Industry Association, photovoltaic energy has the potential to contribute up to 13% to the global electricity supply by 2040. A part of this electricity production will come from thin-film photovoltaic technologies. From various thin-film technologies available on the market today, low-cost cadmium telluride photovoltaics (CdTe-PV) can be considered the market leader with a market share of 5% at annual production. There are however two major concerns about this technology: first, the potential negative environmental impacts of cadmium contamination from CdTe-PV; and second, the possible shortage of the metal tellurium in the future. To overcome the shortage of tellurium, studies have been made to recycle the tellurium from CdTe modules. It has been said in the paper that with this recycling even with the growing market of CdTe, the total tellurium demand will start to decline after 2020. Thus, the CdTe-PV industry has the potential to fully rely on tellurium from recycled end-of-life modules by 2038.
The highlights of the study estimating future recycling flows of tellurium from CdTe-PV waste are:
- At present, overspray from CdTe deposition is the largest waste stream.
- The Te demand, after peaking around 2020, is expected to decline.
- Even at peak times a supply shortage of Te is implausible.
- The CdTe-PV industry could rely on Te from recycled end-of-life modules by 2038.
Life cycle materials and water management for CdTe photovoltaics[14][edit | edit source]
This paper summarizes the material management aspect related to CdTe technology. It gives information on actively managing raw materials throughout the product life cycle can help to manage cost and conserve resources for large-scale PV deployment. The recent developmental research made on this technology includes solar cell and module efficiency being increased to 19.6% and 16.1%, respectively. Future projections include improving CdTe solar cell efficiency to 22% as well as achieving an average CdTe production line module efficiency of 17% by 2017. It introduces the factor of life cycle materials management is water management, where specific strategies include minimizing electricity use in PV module manufacturing, improving PV module efficiency, deploying tracking systems, developing a water balance for PV manufacturing facilities, minimizing grading during construction, using dry brush cleaning methods during operation, and recycling end-of-life systems.
The concern is to actively managing raw materials throughout the product life cycle can help to manage cost and conserve resources for large-scale PV deployment. In the case of cadmium telluride (CdTe) PV, semiconductor materials can undergo nearly closed loop materials management. Cadmium is obtained from the waste by-products of zinc refining, and tellurium from the waste by-products of copper refining. After being compounded and deployed in CdTe PV modules, CdTe can be recycled with approximately 95% yield from end-of-life modules. After further refining to semiconductor-grade purity, the CdTe is reused in the production of new PV modules. It estimates that from 2013 to 2017, module cost per Watt is to decline from $0.63–0.66 to $0.38–0.41 through a combination of increased line utilization and throughput, improved module conversion efficiency, and variable cost reduction. Over the same period, utility-scale system cost is projected to decline from $1.59 to $0.99 per Watt due to the module as well as balance of system (electrical, structural, design, and project-specific) cost reductions.
It also give information in tables which compares factors like efficiencies, open circuit voltage, fill factor and material inventory required for CdTe technology.
FIRST SOLAR SETS CdTe MODULE EFFICIENCY WORLD RECORD[15][edit | edit source]
First Solar, Inc. today announced it set a new world record for cadmium-telluride (CdTe) photovoltaic (PV) module conversion efficiency, achieving a record 16.1 percent total area module efficiency in tests confirmed by the U.S. Department of Energy's National Renewable Energy Laboratory (NREL). The new record is a substantial increase over the prior record of 14.4 percent efficiency, which the Company set in January 2012. Separately, First Solar also set a record for CdTe open circuit voltage (VOC), a critical parameter for PV performance, reaching 903.2 millivolts (mV) in NREL-certified testing. This new record marks the first substantial increase in CdTe VOC in over a decade of international R&D. The new records come just six weeks after First Solar announced a new world record for CdTe solar cell efficiency of 18.7 percent.
Copper indium gallium selenide solar cells[16][edit | edit source]
Copper indium gallium selenide (CuInxGa1-xSe2 or CIGS) is a direct bandgap semiconductor useful for the manufacture of solar cells. Because the material has a high absorption coefficient and strongly absorbs sunlight, a much thinner film is required than of other semiconductor materials. Devices made with CIGS belong to the thin-film category of photovoltaics (PV).CIGS is one of three mainstream thin-film PV technologies, the other two being cadmium telluride and amorphous silicon. CIGS is a I-III-VI2 compound 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. The bandgap varies continuously with x from about 1.0 eV (for copper indium selenide) to about 1.7 eV (for copper gallium selenide).
CIGS is mainly used in the form of polycrystalline thin films. The best efficiency achieved as of October 2013 was 20.8%. A team at the National Renewable Energy Laboratory achieved 19.9% new world record efficiency. These efficiencies are different from module conversion efficiencies. Two of the leading manufacturers of CIGS thin-film PV have hit new record highs in module conversion efficiencies. The U.S. National Renewable Energy Laboratory has confirmed 13.8% efficiency of a large-area (meter-square) production panel, and 13% total-area (and 14.2% aperture-area) efficiency with some production modules. In September 2012 the German Manz AG presented a CIGS solar module with an efficiency of 14.6 % on total module surface and 15.9 % on aperture, which was produced on a mass production facility. MiaSolé obtained a certified 15.7% aperture-area efficiency on a 1m2 production module, and Solar Frontier claimed a 17.8% efficiency on a 900 cm2 module. The use of gallium increases the optical band gap of the CIGS layer as compared to pure CIS, thus increasing the open-circuit voltage. In another point of view, gallium is added to replace as much indium as possible due to gallium's relative availability to indium. Advantage of CIGS compared to CdTe is smaller amount of toxic material cadmium are present in CIGS cells.
References[edit | edit source]
- ↑ "Abundance in Earth's Crust". WebElements.com. Archived from the original on 9 March 2007. Retrieved 2007-04-14
- ↑ U.S. Geological Survey: Mineral commodity summaries 2013; U.S. Geological Survey: Washington, DC, 2013
- ↑ CYRUS WADIA, A. PAUL ALIVISATOS, AND DANIEL M. KAMMEN, Environ. Sci. Technol. 2009, 43, 2072–2077
- ↑ M.A. Green, K. Emery, Y. Hishikawa,W.Warta, E.D. Dunlop (2013). "Solar cell efficiency tables (version 42)|". Progress in Photovoltaics: Research and Application 21: 827–837.
- ↑ http://en.wikipedia.org/wiki/Silicon
- ↑ Zhao, J., A. Wang, P. Altermatt, and M. A. Green. "Twenty‐four Percent Efficient Silicon Solar Cells with Double Layer Antireflection Coatings and Reduced Resistance Loss." Applied Physics Letters 66, no. 26 (June 26, 1995): 3636–3638. doi:10.1063/1.114124
- ↑ http://scitation.aip.org/content/aip/journal/apl/73/14/10.1063/1.122345
- ↑ Jianhua Zhao,* Aihua Wang and Martin A. Green, PROGRESS IN PHOTOVOLTAICS: RESEARCH AND APPLICATIONS Prog. Photovolt: Res. Appl. 7, 471±474 (1999)
- ↑ http://en.wikipedia.org/wiki/Polycrystalline_silicon
- ↑ http://en.wikipedia.org/wiki/Cadmium_telluride_photovoltaics
- ↑ M. Raugei and V. Fthenakis (2010). "Cadmium flows and emissions from CdTe PV: future expectations". Energy Policy: 5223–5228
- ↑ Zweibel, K. (2010), Science 7 May 2010: Vol. 328 no. 5979 pp. 699-701 DOI: 10.1126/science.1189690
- ↑ Max Marwede and Armin Reller (2012), Resources, Conservation, & Recycling 69: 35–49.
- ↑ Sinha, P. (2013). "Life cycle materials and water management for CdTe photovoltaics". Solar Energy Materials & Solar Cells 119: 271–275
- ↑ http://web.archive.org/web/20161002014259/http://investor.firstsolar.com/releasedetail.cfm?ReleaseID=755244
- ↑ http://en.wikipedia.org/wiki/Copper_indium_gallium_selenide_solar_cells#cite_ref-1