Berlin 2012 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 45: Photovoltaics: Silicon-based Systems I

HL 45.2: Vortrag

Mittwoch, 28. März 2012, 09:45–10:00, ER 270

Microstructuring of silicon with femtosecond laser pulses — •Waldemar Freund¹, Jan P. Richters², Jürgen Gutowski¹, and Tobias Voss¹ — ¹Institute of Solid State Physics, Semiconductor Optics Group, Universitiy of Bremen — ²Department of Physics, University of Grenoble

"Black silicon" has been a field of intense studies in recent years. To fabricate this material, a crystalline p-doped silicon wafer is structured with ultrashort laser pulses in a sulfurhexafluoride (SF₆) atmosphere. The physics on the ultrashort time scale results in two processes: the formation of laser-induced periodic surface structures (LIPPS) and the simultaneous doping of the silicon with sulfur far above the solubility limit creating a p-n⁺-junction which acts as a solar cell under illumination. The periodic surface structures considerably enhance light absorption in "black silicon" at energies below the silicon bandgap. The extremely high doping with sulfur results in the formation of a distinct defect band which is the origin of high absorptance in the near-infrared spectral region. Silicon treated with this process therefore constitutes a promising material for applications in thin film solar cells. We show experimental results on optimization of black-silicon solar cell efficiency through passivation of surface defects after treatment with HF. A significant increase in short circuit current of black silicon solar cells is observed when using thinner p-silicon substrates. Our studies represent important steps towards the fabrication of efficient thin-film solar cells with increased infrared sensitivity on base of easy-to-produce black silicon.