Bandgap Engineering of Silicon Quantum Dot Nanostructures for High Efficient Silicon Solar Cell: The Tandem Approach
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1121-N08-04
Bandgap Engineering of Silicon Quantum Dot Nanostructures for High Efficient Silicon Solar Cell: The Tandem Approach
B. Rezgui, A. Sibai, T. Nychyporuk, O. Marty, M. Lemiti and G. Brémond Institut des Nanotechnologies de Lyon (INL), Université de Lyon, CNRS UMR-5270,
INSA LYON, 7 avenue Jean Capelle 69621 Villeurbanne, France.
ABSTRACT In this work, we use wide bandgap engineering based on the quantum confinement effect in silicon quantum dot nanostructures to develop an all-silicon tandem solar cells. A method of in situ growth of silicon quantum dots (Si QDs) within silicon nitride films deposited by plasma-enhanced chemical vapour deposition (PECVD) has been shown using high resolution transmission electron microscopy (HRTEM). Photoluminescence (PL) measurements show the quantum confinement in silicon nanostructures in agreement with the increase of the PL energy with reduction in dot size. In addition, the effect of substrate temperature on the formation and evolution of Si QDs during the PECVD deposition was investigated. Finally, the choice of the best architecture of a tandem solar cell is discussed. INTRODUCTION Nanoscale silicon structures have received attention as promising materials for optoelectronic applications [1,2]. These nanostructures include porous silicon, silicon superlattices and silicon quantum dots. Recently, efforts have been devoted to the development of Si QDs embedded in a dielectric matrix that promise efficient photovoltaic conversion in the blue region of the solar spectrum [3]. Different approaches have been proposed in order to improve solar cell performance by reducing the most important losses in single-bandgap cells that are the inability to absorb photons with energy less than the bandgap and the thermalization of photon energies exceeding the bandgap. These third generation’s approaches aim to increase the efficiency of the photovoltaic device and, hence reducing the cost (per Watt peak) of thin film second generation technology. One of the third generation solar cells architecture that take advantage of nanoscale structures is the so-called tandem solar cell [4]. The main aim of this approach is to absorb a larger part of the solar spectrum and hence to increase the efficiency of the device. Our goal is to engineer wide bandgap for silicon-based materials using quantum confinement in nanostructures in order to realize an “all-silicon” tandem solar cell based on Si QDs. However, controlled fabrication of silicon nanostructures constitutes one of the main technological challenges toward the realization of the top cell in the tandem solar cell device. Oxide (SiOx) has been widely used as a surrounding matrix of nanosilicon structures [5,6]. However, silicon nitride is of interest as it would provide a lower potential barrier and possibly improve electronic transport between QDs. On the other hand, this technique is a low-temperature process which allows quantum dots to form during deposition without the need for a subsequent high temperature anneal. In the present
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