Generation Mechanism of Inhomogeneous Minority Carrier Lifetime Distribution in High Quality mc-Si Wafers and the Impacts on Electrical Performance of Wafers and Solar Cells

doi:10.1016/j.jmst.2015.07.015

Abstract

Abstract: To find out the causation of inhomogeneous minority carrier lifetime distribution in high quality multicrystalline silicon (mc-Si) wafers, impurities and lattice defects were systematically studied by means of Fourier transform infrared (FTIR) spectroscopy and metallography. Inhomogeneously distributed oxygen impurity and dislocations were demonstrated to be key leading factors, and the restriction mechanism was discussed. Scattering process caused by ionized impurities and dislocations decreased carrier mobility, while carrier concentration was not significantly affected. Measurements showed that resistivity was higher and more dispersive in low lifetime area. Solar cells were fabricated with these wafers. Cells' efficiency of inhomogeneous ones exhibited averagely 0.27% lower than the regular ones in absolute terms. Recombination centers and leakage loss induced by dislocations and impurities led to the reduction in shunt resistors and open-circuit voltage, and then affected the performance of cells.

Key words: mc-Si wafers, Minority carrier lifetime, Oxygen impurity, Dislocation

Xianxin Liu, Genghua Yan, Ruijiang Hong. Generation Mechanism of Inhomogeneous Minority Carrier Lifetime Distribution in High Quality mc-Si Wafers and the Impacts on Electrical Performance of Wafers and Solar Cells[J]. J. Mater. Sci. Technol., 2015, 31(11): 1094-1100.

Figures/Tables 12

Minority carrier lifetime mapping of 6 high quality mc-Si wafers by WT-2000: (a) sample a, (b) sample b, (c) sample c, (d) sample d, (e) sample e, (f) sample f.

Homogeneous distribution of Fe impurity measured by WT-2000.

Regression model between Fe concentration and minority carrier lifetime.

Carbon and oxygen concentration in area A and area B samples measured by FTIR.

Lattice defects observed by optical microscopy: (a) and (b) large-angle GBs, (c) crystal twinning, (d) stacking faults, (e) small-angle GBs, (f) dislocations.

Mass crystal defects observed on the area A sample: (a) magnification: 50, (b) magnification: 500.

Comparison of the dislocations density in area A samples and area B samples: (a-e) area A samples, (f) area B sample.

Carrier mobility and resistivity in area A samples and area B samples measured by Hall.

Resistivity confidence ellipses in area A and B samples measured with the four-probe method.

Performances of the cells with homogeneous and inhomogeneous minority carrier lifetime.

Infrared thermal mapping and electroluminescence (EL) tests results: (a) infrared thermal mapping of the area A sample, (b) corresponding EL mapping, (c) corresponding lifetime mapping.

Internal quantum efficiency (IQE) of three samples with different current densities.

References

[1] V. Osinniy, P. Bomholt, A. Nylandsted Larsen, E. Enebakk, A.K. Søiland, R. Tronstad, Y. Safir,Sol. Energy Mater. Sol. Cells, 95 (2011), pp. 564-572
[2] J. Hofstetter, J.F. Lelièvre, C. del Canizo, A.D. Luque, Mater. Sci. Eng, B159 (2009), pp. 299-304
[3] D. Macdonald, A. Cuevas, A. Kinomura, Y. Nakano, L.J. Geerligs,J. Appl. Phys, 97 (2005), p. 033523
[4] I.D. Kovalev, T.V. Kotereva, A.V. Gusev, V.A. Gavva, D.K. Ovchinnikov,J. Anal. Chem, 63 (2008), pp. 248-252
[5] F.S. d'Aragona,J. Electrochem. Soc, 119 (1972), pp. 948-951
[6] J. Chen, T. Sekiguchi, D. Yang, F. Yin, K. Kido, S. Tsurekawa,J. Appl. Phys, 96 (2004), pp. 5490-5495
[7] W. Seifert, G. Morgenstern, M. Kittler,Semicond. Sci. Technol, 8 (1993), pp. 1687-1691
[8] A.A. Istratov, H. Hieslmair, E.R. Weber,Appl. Phys. A-Mater. Sci. Process, 70 (2000), pp. 489-534
[9] D.E. Aspnes, T.S. Moss,Handbook on Semiconductors,(second ed.)North-Holland, Amsterdam (1980)
[10] J.Y.W. Seto,J. Appl. Phys, 46 (1975), pp. 5247-5254
[11] C. Hassler, H.U. Hofs, W. Koch, G. Stollwerck, A. Muller, D. Karg, G. Pensl,Mater. Sci. Eng. B, 71 (2000), pp. 39-46
[12] K. Bothe, R. Hezel, J. Schmidt,Appl. Phys. Lett, 83 (2003), pp. 1125-1127
[13] K. Bothe, R. Sinton, J. Schmidt,Prog. Photovolt. Res. Appl, 13 (2005), pp. 287-296
[14] M. Sheoran, A. Upadhyaya, A. Rohatgi,Solid State Electron, 52 (2008), pp. 612-617
[15] H.J. Moller, C. Funke, A. Lawerenz, S. Riedel, M. Werner,Sol. Energy Mater. Sol. Cells, 72 (2002), pp. 403-416
[16] A.K. Singh,Electronic Devices and Integrated Circuits,(first ed.)PHI Learning Pvt. Ltd., Delhi (2011)
[17] D. Ferry,Semiconductor Transport,(third ed.)CRC Press, Ohio (2000)
[18] D.S.H. Chan, J.C.H. Phang,IEEE Trans. Electron Dev, 34 (1987), pp. 286-293
[19] O. Breitenstein, J.P. Rakotoniaina, M.H. Al Rifai, M. Werner,Prog. Photovolt. Res. Appl, 12 (2004), pp. 529-538
[20] K. Hartman, M. Bertoni, J. Serdy, T. Buonassisi,Appl. Phys. Lett, 93 (2008), p. 122108
[21] H.J. Moller, T. Kaden, S. Scholz, S. Wurzner.Appl. Phys. A-Mater. Sci. Process, 96 (2009), pp. 207-220
[22] M. Akatsuka, M. Okui, N. Morimoto, K. Sueoka,Jpn. J. Appl. Phys. Pt. 1, 40 (2001), pp. 3055-3062