B implanted emitters are investigated in the back junction cell configuration and their material properties are tested in double side implanted Si wafers. B has been implanted at 5 keV at various dose conditions varying from 1 × 1014 up to 3 × 1015 at./cm2 and activated at 1000°C for 10 min. N‐type 8 × 8 cm2 mono‐crystalline cells are fabricated and measured. Both fill factor and efficiency increase for high‐B doses. However, at 1015 at./cm2 B dose the Voc drops, which is in agreement with lifetime degradation in the wafer. Defect evolution simulations of BnIm clusters formation is correlated with lifetime degradation. Copyright © 2011 John Wiley & Sons, Ltd.

The studies of porous silicon as a one-dimensional photonic crystal have led to solutions allowing the fabrication of broad photonic band gaps as large as several hundreds nanometers for various types of applications. In this work we demonstrate the use of the chirping process, i.e., the gradual increase in the spatial period of the structure, as it is used in image processing, to design porous silicon broad-band reflectors for thin-film silicon solar cells. Modeling of those layers is done using linear design method and a simulation software. Such chirped structures are fabricated by an anodization process. Samples are prepared on mono and multicrystalline silicon substrates with 15, 40, 60, and 80 layers. The reflectance spectra of such prepared porous reflectors are evaluated and the results show an increase in bandwidth of over 50% of the total width in comparison with the conventional, unchirped reflectors. We demonstrate clear advantages of introducing chirped multilayer structures over conventional ones. Although some understanding of chirping exists mainly in the field of image processing and photonics, detailed study of chirped porous structures as broad-band reflectors is needed for their implementation in thin-film epitaxial silicon solar cells. A record efficiency of almost 14% was reached for those types of reflectors on a large area 71 cm2 epitaxial Si solar cell, giving a boost in efficiency of 0.6% absolute in comparison with the solar cells containing conventional reflectors.

We demonstrate the use of a copper-based metallization scheme for the specific application of thin-film epitaxial silicon wafer equivalent (EpiWE) solar cells with rear chemical vapor deposition emitter and conventional POCl 3 emitter. Thinfilm epitaxial silicon wafer equivalent cells are consisting of high-quality epitaxial active layer of only 30 µm, beneath which a highly reflective porous silicon multilayer stack is embedded. By combining Cu-plating metallization and narrow finger lines with an epitaxial cell architecture including the porous silicon reflector, a J sc exceeding 32 mA/cm 2 was achieved. We report on reproducible cell efficiencies of >16% on >70-cm 2 cells with rear epitaxial chemical vapor deposition emitters and Cu contacts.

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