Light trapping in amorphous silicon solar cells on plastic substrates
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H6.14.1
Light trapping in amorphous silicon solar cells on plastic substrates Vanessa Terrazzoni-Daudrix, Joelle Guillet, Xavier Niquille, Arvind Shah IMT University of Neuchâtel, Breguet 2, CH-2000 Neuchâtel, Switzerland / E-mail: [email protected] R. Morf, PSI (Paul Scherrer Institut), Villigen, CH-5232, Switzerland A.Tishchenko, V. Brioude, O. Parriaux TSI Laboratory, Jean Monnet University, F-42023 Saint-Etienne D. Fischer VHF Technologies SA EICN, avenue de l’hôtel de ville 7, CH-2400 Le Locle, Switzerland ABSTRACT
In order to simultaneously decrease the production costs of thin film silicon solar cells and obtain higher performances, the authors have studied the possibility to increase the light trapping effect within thin film silicon solar cells deposited on flexible plastic substrates. In this context, different nano-structure shapes useable for the back contacts of amorphous silicon solar cells on plastic substrates have been investigated: random textures and gratings. The optimisation of such back reflectors is so far empirical. Gratings constitute a well-known optical technique and their light trapping effect can be optimised by simulation. A first conclusion is that neither the traditional “Haze factor” determined in air for a wavelength of 650nm nor the “rms roughness” of the surfaces are sufficient as criteria to optimise the back contact roughness for light trapping in cells. The shape of grains is a further essential criterion. The authors have so far obtained a relative current enhancement of 16% for solar cells deposited on randomly textured polyethylene terephthalate (PET) as compared to a corresponding conventional solar cell co-deposited on a flat mirror (Ag) on glass. Solar cells on PET with 6.3% stabilized efficiency have until now been obtained. Theoretical calculations indicate that gratings can enhance the current of a-Si solar cells by up to 30 percent.
INTRODUCTION In order to simultaneously decrease the production costs of thin-film silicon solar cells and obtain higher performances, the authors have studied the possibility to increase the efficiency (η) of n-i-p solar cells deposited on Poly(Ethylene Terephtalate) (PET). The advantages of this flexible organic polymer are first, its low price compared to more conventional substrates like Polyimide (PI), stainless steel, or glass, and second, its compatibility with roll to roll processes. However, its main drawback is the fact that it can not be heated to temperatures more than 200°C during the deposition of solar cells. Different studies have, on the other hand, already shown that depositing amorphous silicon solar cells at low temperatures has a detrimental effect on their short circuit current (Isc) [1, 2, 3].
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H6.14.2
In this context the authors studied different kinds of textured
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