The general strategy is to judiciously choose the band gaps, the band offsets, and thicknesses of the individual layers. Hetero-structures between a-Si:H layer and c-Si wafer referred to as HIT (Hetero-junction with Intrinsic Thin film layer) cells have also been developed and currently hold the record efficiency for crystalline Si. The as-deposited precursor films were directly subjected to annealing (without postannealing sulfurization) at temperatures ranging from 150 to 550°C for 1 hour in argon atmosphere. A variant of CIGS is copper indium diselenide. 8 illustrates that the energy gap of CdTe is around 1.45 eV, which is in principle well suited to solar energy conversion. doi Typical CdTe thin-film deposition techniques include: close-spaced sublimation, vapor-transport deposition, physical-vapor deposition, sp… /DR << �x������- �����[��� 0����}��y)7ta�����>j���T�7���@���tܛ�`q�2��ʀ��&���6�Z�L�Ą?�_��yxg)˔z���çL�U���*�u�Sk�Se�O4?׸�c����.� � �� R� ߁��-��2�5������ ��S�>ӣV����d�`r��n~��Y�&�+`��;�A4�� ���A9� =�-�t��l�`;��~p���� �Gp| ��[`L��`� "A�YA�+��Cb(��R�,� *�T�2B-� effects of ITO layers of various thicknesses on the performance of CdS/CdTe solar cells are also studied. The particularly suitable optoelectronic properties of CdTe are still driving the attention of both scientific communities and industrial companies in the highly competitive world of PV materials. The high quantum efficiency for CdTe/CdS TFSC lies in the range of 500–850 nm of the solar spectrum. Figure 18.1. >> converted to PDF/A-2b PDF/X ID Schema The energy gap of CdS is 2.42 eV. The Cu treatment was performed by thermally evaporating a ~4 nm thick Cu layer before depositing a Au back contact layer, and then annealing at 150 °C for 45 min in a dry air ambient. internal solar cell performance and not necessarily on completely characterizing the CSS process. << This plot is courtesy of the National Renewable Energy Laboratory, Golden, CO, USA. CZTS, Cu2ZnSnS4; SLG, soda lime glass. These observations inspired the development of a post deposition treatment (PDT) which led to increased efficiencies of >20% [16–18]. /S /GTS_PDFA1 A cross section of a CdTe solar cell is shown in Fig. However, the thin CdTe/CdS layers are stable and solid, and are safely encapsulated between thick layers of glass or plastic. /Kids [24 0 R] endingPage << 8 0 obj • Zincblend structure • Direct energy gap 1.44 eV • Can be growth both p-type (VCd acceptors) or n-type (Cd i donors) • me = 0.1 m0 • µe = 1100 cm2/Vs in single crystals • Difficult extrinsic doping • ηth = 31% Source: Wikipedia. 2.3 Solar Cell Device Physics 18 2.4 Estimation of Rs, Rsh and Identification of Back Barrier 22 CHAPTER THREE: PROCESSING OF CdS/CdTe SOLAR CELLS 24 3.1 Device Fabrication 24 3.2 Properties of Different Layers of Cell Structure 25 Due to the ease and speed of its production CdTe offers the least payback time <1 year among all competing technologies including c-Si, thus making it one of the fastest growing technologies. the open circuit voltage (Voc) of CdTe NC solar cells has stagnated below 0.7 V, which is significantly lower than most CdTe thin film solar cells fabricated by vacuum technology (around 0.8 V~0.9 V). A range of the deposition parameters is included in Table 1. Text 9. High mobility is important because, together with high charge carrier lifetimes, it means that the light-generated electrons and holes can move large enough distances to be extracted as current, instead of losing their energy as heat within the cell [19]. Films were coated without stirring at room temperature, in a conventional three-electrode cell assembly. Ending page Third, 40–200 nm thick Au layers were deposited as back contacts for solar cell performance evaluation. NREL has a world-class assembly of CdTe photovoltaic research tools and expertise. 10 0 obj The CdS layer must therefore be stable enough to this recrystallization and intermixing … /BaseFont /ZapfDingbats 8. CdTe solar cells clearly have a lot going for them but there remains a number of key technological challenges that, if overcome, could push the conversion efficiencies closer to the theoretical maximum of >30%. copyright The Cu–Zn–Sn precursors were then deposited in a one step process at room temperature without stirring in a conventional three-electrode cell assembly and the entire system was annealed in elemental sulfur under N2 atmosphere at 600°C for 2 hours. Vasilis M. Fthenakis, in McEvoy's Handbook of Photovoltaics (Third Edition), 2018. Mirrors crossmark:CrosMarkDomains springerlink.com When CIGS is grown on Mo an interface layer of MoSe2 is automatically formed which helps in ohmic transport between CIGS and Mo. InstanceID >> 4) The lower carrier lifetime in CdTe is considered to be responsible for the huge V OC deficit. These structures were depicted as the following: FTO/CdS/CdTe/Au corresponding to sample 1, FTO/CdS/CdTe/BC/Au corresponding to sample 2, and FTO/MZO/CdS/CdTe/BC/Au corresponding to sample 3, respectively. Company creating the PDF internal /Subtype /XML http://prismstandard.org/namespaces/basic/2.0/ Schematic presentation of CdTe/CdS solar cell in “superstrate” configuration showing different layers and their nomenclature. Figure 18.2. CrossmarkDomainExclusive The manufacture of a typical thin film CdTe solar cell starts with a perfectly clean glass substrate.3 Onto this is first sprayed a Transparent Conducting Oxide (often referred to as the TCO) layer. >> X-ray diffraction revealed a kesterite structure for films with large grains (average grain size of 2 µm), densely packed, and well-distributed over the entire substrate surface. /CrossMarkDomains#5B1#5D (springer.com) However, in the state-of-the-art CdTe solar cells, the open-circuit voltage (V OC) is 880 mV, which is only 76.1% of the Shockley–Queisser (SQ) limit of 1157 mV. Panasonic manufactured a cell of “practical size” (101 cm2) with an efficiency of 26.7% [7]. Efficiency as high as 16.5% has been achieved in CdS/CdTe heterojunction structure in laboratory in 2001, and current techniques for CdS/CdTe solar cells gradually step toward commercialization. Fig. sputtering. The copper layer was deposited from an alkaline solution made of copper chloride, sodium hydroxide, and sorbitol [120]. /Icircumflex /Idieresis /Eth /Ntilde /Ograve /Oacute /Ocircumflex /Otilde /Odieresis /multiply seq Text Recently, alternative back contact materials have been explored but industrial production is still based on Mo layers. Manufacturing solar cells from thin film materials is much easier than making them from solid semiconductor substrates because they can either be produced by vapor deposition techniques, by sputtering, or in some cases by printing. Then a layer of p-type CdTe is added. Fig. Text In the “superstrate” configuration, the a-Si cell is grown in the p-i-n sequence onto a transparent substrate. volume Schematics of a typical superstrate CdS/CdTe solar cell structure. Very famous low-cost methods such as electrodeposition (ED), screen printing, and chemical spraying (CS) are done around 450°C and classified as low temperature processes. << Inhalation is probably the most important pathway, because of the larger potential for exposure, and higher absorption efficiency of Cd compounds through the lung than through the gastrointestinal tract. /Count 10 endobj As with most thin-film solar technologies, carrier collection is accomplished by drift, or field-assisted collection. They sequentially deposited metal layers of Cu, Sn, and Zn on Mo-coated SLG substrates at room temperature without stirring. This structure is similar to the heterojunction in CIGS cells. The CdCl2 heat treatment was performed by applying a CdCl2 powder (Sigma Aldrich, 99.99%)/methanol saturated solution onto the surface of the CdTe film, and then annealing at 390 °C for 30 min in a dry air ambient. /Type /Font seq Text >> The downside of this technology is the processing of the absorber at relatively higher temperatures >450°C. ID of PDF/X standard The NREL solar cell efficiency chart. have shown the possibility of preparing CZTS thin films by a single step coelectrodeposition of the metals as well as the sulfur. GTS_PDFXConformance 44.16 illustrates the different morphologies of sequential depositions of three layers. Trapped Fig. It is quite notable that even though important dissimilarities exist, the performances attained are independent to processing illustrating the versatility of CdTe and its superior prospects in the PV technologies. While it is readily available today, the U.S. Department of Energy has predicted a shortfall by 2025. SEM images of precursor metal layers (A) Cu on Mo, (B) Sn on Cu, (C) Zn on Sn [66]. publicationName 7 0 obj /quotesingle 96 /grave 128 /bullet /dagger /daggerdbl /ellipsis /emdash /endash << Text From Shockley Queisser diagram, CdTe with a band gap of 1.45eV has the potential to yield a theoretical high efficiency. pdfx The as-grown CdTe solar cells were synthesized following the steps below: First, on commercial fluorine doped SnO2-coated soda lime glass substrates, ~100 nm thick CdS window layers were deposited by R.F. The common identifier for all versions and renditions of a document. No oxide impurities were found in films, contrary to those electrodeposited from aqueous solutions. The CdTe is most attractive for its chemical simplicity and the robust stability. << /PDFDocEncoding 10 0 R A power conversion efficiency of 11.25% was obtained with an open-circuit voltage of 0.72 V, as shown in Table 2.4 [21]. Two types of precursor films were investigated which were either Cu-poor or Cu-rich. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. URL: https://www.sciencedirect.com/science/article/pii/B9780128114797000105, URL: https://www.sciencedirect.com/science/article/pii/B9780128196106000028, URL: https://www.sciencedirect.com/science/article/pii/B9780128040041000099, URL: https://www.sciencedirect.com/science/article/pii/B9780128133514000468, URL: https://www.sciencedirect.com/science/article/pii/B9780124095489100922, URL: https://www.sciencedirect.com/science/article/pii/B9780128029534000020, URL: https://www.sciencedirect.com/science/article/pii/B9780128099216000355, URL: https://www.sciencedirect.com/science/article/pii/B978012811479700018X, URL: https://www.sciencedirect.com/science/article/pii/S1369800116301925, A Comprehensive Guide to Solar Energy Systems, Hervé J. Tchognia Nkuissi, Bouchaib Hartiti, in, Handbook of Nanomaterials for Industrial Applications, Sustainable Energy Technologies & Sustainable Chemical Processes, Overview of the PV Industry and Different Technologies, Senthilarasu Sundaram, ... Tapas Kumar Mallick, in, McEvoy's Handbook of Photovoltaics (Third Edition), Senthilarasu Sundaram, ... Hari Upadhyaya, in, Advanced transmission electron microscopy for semiconductor and materials science, Materials Science in Semiconductor Processing. So far, the highest efficiencies have been achieved in “superstrate” configuration for CdTe. They employed an aqueous electrolyte solution containing metals salts of CuSO4, ZnSO4, SnSO4, and Na2S2O3 (sulfur source). /Nums [0 16 0 R] CdTe thin film solar cell structure comprises of a p-type CdTe absorber layer and n-type CdS based window layer forming a heterojunction, which has an intermixed interface region. By varying the amounts of copper, indium, and gallium, the bandgap of this material can be changed, and this can be used to tailor the thin film for a specific application. 18.2.2 Cadmium Telluride Solar Cells. Subcontract Report NREL/SR-5200-51380 . /RegistryName () First Solar Inc. (a leading company in CdTe commercialization) PV modules reach more than 10 GWp of module installations worldwide. Na, K into the thin film absorber stack provides an almost 3–4 folds increase in the efficiency which has been a “holy grail” for sometime in the thin film field. And water stable with negligible vapor pressure of CdTe precursors, is a most common n-type layer! Determinant of risk thin film solar cells is still based on Mo an interface layer Pd. Combined with nanocrystalline silicon junctions [ 1 ] and the cross-sectional views of CZTS! Aqueous solutions collection is accomplished by drift, or other publication, in solar photovoltaic production... 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