An electrochemical etching technique has been developed that provides continuous control over the porosity of a porous silicon (PSi) layer as a function of etching depth. Thin films with engineered porosity gradients, and thus a controllable refractive index gradient, have been used to demonstrate broadband antireflection (AR) properties on silicon wafers and solar cell substrates. This low broadband reflectivity is a direct result of the formation of a refractive index gradient at the substrate surface, where the transition between air and silicon occurs continuously throughout the thickness of a PSi film. These graded index films are formed by applying a continuously changing current function to the electrochemical cell during the PSi etch. The application of these films as solar cell AR coatings is of particular interest, where their broadband nature is a critical advantage. For this application, graded index PSi films must not only offer superior AR properties, but must also prove minimally disruptive to the electrical properties of the underlying solar cell. This requirement limits the total thickness of these films to approximately 120 nm, creating several challenges for this process. However, the simplicity and highly reproducible nature of this technique, in combination with its short duration (less than 10 seconds), make it a strong alternative to current vacuum deposited AR coating technology.
This is a preview of subscription content, access via your institution.
Buy single article
Instant access to the full article PDF.
Tax calculation will be finalised during checkout.
A. Krotkus, K. Grigoras, V. Pacebutas, I. Barsony, E. Vazsonyi, M. Fried, J. Szlufcik, J. Nijs, and C. Levy-Clement, Sol. Energy Mat. Sol. Cells 45, 267 (1997).
L. Stalmans, J. Poortmans, H. Bender, M. Caymax, K. Said, E. Vazsonyi, J. Nijs, and R. Mertens, Prog. Photovolt. Res. Appl. 6, 233 (1998).
W. Theiss, Surface Science Reports 29, 91 (1997).
M. Thonissen, M.G. Berber, S. Billat, R Arens-Fischer, M. Kruger, H. Luth, W. Theiss, S. Hillbrich, P. Grosse, G. Lerondel, U. Frotscher, Thin Solid Films 297, 92 (1997).
S. Zangooie, R. Jansson, and H. Arwin, Mat. Res. Soc. Proc. 557, 195 (1999).
M.G. Berger, R. Arens-Fischer, M. Thonisson, M. Kruger, S. Billat, H. Luth, S. Hilbrich, W. Theiss, and P. Grosse, Thin Solid Films 297, 237 (1997).
S. Uehara, K. Kurose, and T. Matsubara, Phys. Stat. Sol. (a) 182, 461 (2000).
C.C. Striemer and P.M. Fauchet, Appl. Phys. Lett. 81, 2980 (2002).
J. Hiller, J.D. Mendelsohn, and M.F. Rubner, Nature Mat. 1, 59 (2002).
S. Chan and P.M. Fauchet, Appl. Phys. Lett., 75, 274 (1999).
J.I. Hanoka, Sol. Energy Mat. Sol. Cells 65, 231 (2001).
R. Jacobsson, in Progress in Optics, vol. 5, edited by E. Wolf (John Wiley & Sons, New York, 1965) pp. 249.
E. Hecht and A. Zajac, Optics (Addison-Wesley, London, 1974) pp. 311.
Handbook of Optical Constants of Solids, edited by E.D. Palik (Harcourt Brace Jovanovich, New York, 1985) pp. 561.
D. Brumhead, L.T. Canham, D.M. Seekings, and P.J. Tufton, Electrochimica Acta 38, 191 (1993).
This work was supported by the National Renewable Energy Laboratory (NREL) under contract #9-18668-06. Technical support and fabrication facilities at the Rochester Institute of Technology and the Cornell Nanofabrication Facility (NSF Grant ECS-9731293) were utilized. Microscopy facilities at the University of Rochester are supported by the National Science Foundation.
About this article
Cite this article
Striemer, C.C., Fauchet, P.M. Exploiting Silicon Porosity Gradients for Superior Antireflective Films. MRS Online Proceedings Library 737, 85 (2002). https://doi.org/10.1557/PROC-737-F8.5