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Characterization of mixed amorphous/nanocrystalline industrial p-i-n solar modules by Fourier transform photocurrent spectroscopy

Mixture of amorphous and nanocrystalline silicon, with different grain size and crystalline fraction was deposited in capacitatively coupled parallel plate reactor using RF discharge in highly diluted silane gas. The layers were integrated into single p-i-n structure of typical solar cell and characterized by Fourier transform photocurrent spectroscopy (FTPS). Purpose of this study is to increase stabilized efficiency of “ standard” industrially produced p-i-n amorphous silicon solar modules. Recently, we have demonstrated the suitability of FTPS for fast measurement of quantum efficiency (QE) of solar cells or individual subcells in the module [1]. This approach is used here to study mainly the homogeneity of the cell structure over the area of 30 x 30cm. Simultaneously, we have checked the absorber quality (defects, disorder and composition) with the help of „ classical“ FTPS [2]. Dependence of QE and optical absorption coefficient upon the size of crystallites, defect density and crystalline fraction was measured and will be discussed. Nanocrystalline fraction up to 30%, as determined from Raman spectra, is not seen in QE or optical absorption spectrum, which leads to speculation about dispersed nanograins structure. On the other hand, such morphology of very small grains in the amorphous matrix is expected to have better stability against light degradation ; this study is underway. A possibility of using this type of material in multijunction structure is discussed too. [1] A. Poruba, R. Barinka, P. Cech, R. Kravets, L. Hoďáková, M. Vaněček, A. Fejfar, Proc. 20th European Photovoltaic Solar Energy Conference, (2005), Barcelona, Spain, Eds.: W. Palz, H. Ossenbrink, P. Helm, p. 240 [2] M. Vanecek and A. Poruba, Appl. Phys. Letters (2002) 719

solar cell; amorphous silicon; nanocrystalline silicon; FTPS

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