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Chapter 18 • Thin Film Photovoltaics  367



                   solar Frontier (Japan) leads the production on Cis technology with annual production
                 capacity over 1 GW and has plans to enter BiPV market with the use of aluminium in place
                 of glass to reduce the weight of the modules.
                 18.2.4  Perovskite

                 Perovskite solar cells stem from dye-sensitized solar cells but have promising solid state
                 structures as well as rapid efficiency leaps (Fig. 18.4), which have now reached 22.7% [2].
                   Most commonly, CH 3 NH 3 PbI 3  based organic–inorganic perovskite materials have been
                 used in these types of solar cells due to their high charge carrier mobility. 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]. Moreover, the perovskite solar
                 cells can be deposited by low-temperature methods such as solution process viz. spin
                 coating, spray deposition, and thermal evaporation methods.


                 18.3  Deposition and Growth Techniques

                 Room temperature deposition allows the use of a variety of substrates such as glass, metal,
                 and plastics but often results in inferior module efficiencies and quality. Two most com-
                 monly used methods for a-si are plasma enhanced chemical vapor deposition (PeCVd)
                 and glow discharge CVd. For high deposition rates the deposition technologies based on
                 very high frequency (VhF), microwave and high-pressure plasma are currently being pur-
                 sued. Alternative deposition methods using hot wire CVd (hWCVd) technique, electron
                 cyclotron resonance reactor (eCR) and also the combination of hWCVd and PeCVd are
                 also being carried out to increase the deposition rate [1,10,20–22]. Vacuum Evaporation is
                 a simple deposition method allowing low temperatures for CdTe and CiGs cells. Vacuum
                 evaporation method involves simultaneous evaporation of the constituent elements from
                 multiple sources in single or sequential processes during the whole absorber deposition
                 process [23]. There is a substantial interest in testing different deposition techniques for
                 CiGs which could improve the technology greatly. some methods include: nanosized pre-
                 cursor particles and electro-deposition from a chemical bath. A hybrid approach that uses
                 additional vacuum deposition on electrodeposited precursor layers has also been inves-
                 tigated [24]. Closed Space Sublimation (CSS) and vapor transport (VT) are the prominent
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                 and industrially used processes for CdTe deposition owing to its very high rate (2–5 µ min )
                 of deposition. First solar is the most successful CdTe company to date with an annual pro-
                                                                                 2
                 duction capacity of approximately 3 GWp for modules on 60 × 120 cm  glass substrates.
                 Ge global research has achieved a ground-breaking efficiency of 19.6% on glass substrates.
                 early  2014  First  solar  communicated  20.4%  solar  cell  efficiency  and  a  very  remarkable
                 full scale module efficiency of 17%. details of other alternative methods such as screen-
                 printing, spray pyrolysis, moCVd, CVd and atomic layer deposition (ALd) and electro-
                 deposition (ed) are also possible [11,13,23,24]. For flexible substrates such as polymers low
                 temperature methods like sputtering, hVe, and electro-deposition (ed) are suitable.
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