ISBN 978-3-8439-2866-3

978-3-8439-2866-3, Reihe Physik

Thomas Gimpel
Preparation and characterization of femtosecond laser sulfur doped silicon solar cells

101 Seiten, Dissertation Technische Universität Clausthal (2016), Softcover, A5

Zusammenfassung / Abstract

This thesis investigates the morphological, optical, electrical and optoelectronical properties of femtosecond laser sulfur-hyperdoped silicon with regard to intermediate band photovoltaic devices. The challenge of implementing such a laser process is to maintain a high charge carrier lifetime, while simultaneously increasing the absorption of photons with energies below the silicon band gap. Sulfur emitter solar cells are prepared in a single-junction configuration, reaching efficiencies of 8.2%. By adding an extra emitter into a conventional single-junction silicon solar cell, a tandem solar cell device is formed, with an efficiency of 14.9%. The effect of annealing on energy conversion within the standard and the sub-band gap spectral range of silicon is investigated. For wavelengths with energies below the band gap, the external quantum efficiency is optimized by an adequate annealing regime. Losses are found to be reduced during annealing due to sulfur diffusion and structural changes within the silicon lattice. The phase change in silicon after femtosecond laser irradiation and subsequent annealing is revealed by Electron Backscatter Diffraction. Intrinsic defects are passivated with the help of an atomic layer-deposited aluminumoxide, thus, achieving charge carrier lifetimes of 24 μs. The findings of this work can be used to improve today’s silicon photovoltaics by implementing the laser process in an industrial production environment. With regard to this purpose, a high-throughput process is developed in this thesis, achieving an area scan velocity of 6.7 cm^2/s .