Abstract
In periodic stacks of planar bilayers in which the high-index layers are made of an optically absorbing material, the phenomenon of slow light can be exploited in order to enhance absorption of the light in the high-index layers by suitably locating the red edge of the photonic band gap in the spectral region where the extinction coefficient is high. This concept is theoretically demonstrated here in the case of a Bragg resonator made of alternating layers of active (photovoltaic) high-index material and passive (transparent conductive oxide) low-index material. The transfer-matrix formalism is used to calculate the absorption spectrum of the Bragg resonator from which the maximum achievable photo-current is determined. In comparison with a reference slab of identical thickness of active material, we demonstrate that the photo-current can be enhanced provided that the layer thicknesses and the number of layers are suitably chosen. Highest enhancement values (factor of 2.5) are obtained for very thin layers of active material and a few layers only. Therefore, this concept is regarded as a promising way to increase the efficiency of realistic thin-film planar solar cell structures at reduced fabrication costs.
© 2012 Optical Society of America
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