New Si-based multilayers for solar cell applications
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NANO EXPRESS
Open Access
New Si-based multilayers for solar cell applications Ramesh Pratibha Nalini, Christian Dufour, Julien Cardin, Fabrice Gourbilleau*
Abstract In this article, we have fabricated and studied a new multilayer structure Si-SiO2/SiNx by reactive magnetron sputtering. The comparison between SiO2 and SiNx host matrices in the optical properties of the multilayers is detailed. Structural analysis was made on the multilayer structures using Fourier transform infrared spectroscopy. The effect of specific annealing treatments on the optical properties is studied and we report a higher visible luminescence with a control over the thermal budget when SiO2 is replaced by the SiNx matrix. The latter seems to be a potential candidate to replace the most sought SiO2 host matrix. Introduction The third generation of solar cells aims at reducing the cost and at improving the efficiency. Thin film solar cells based on silicon nanostructures is one of the most researched system to achieve such a target [1-3]. Ever since the discovery of the visible luminescence of the porous Si by Canham [4] various research groups have exploited the room temperature photoluminescent nature of silicon by fabricating different kinds of Si-based nanostructures. The luminescence is attributed to the quantum confinement of carrier in Si-nanoclusters (Sinc) [5-8]. Among the methods of obtaining the Si nanostructures we cite electrochemical etching [4,9], fabrication of silicon dots by plasma sputtering technique [10], and multilayer approach [8,11,12]. The important part of the ongoing research involves Si-nc embedded in an amorphous matrix such as SiO2, SiNx, or amorphous silicon. Though Si-nc embedded in SiO2 is the most common structure, the problem of carrier injection in this matrix comes as a major drawback owing to the large band gap of SiO2. Hence the replacement of SiO2 by other dielectric matrices with smaller bandgap turns out to be a solution. SiNx matrix meets up these requirements and hence Si-nc embedded in SiN x matrix has become a material of choice in the recent past. In this article, we develop a new multilayer composition silicon-rich silicon oxide (SRSO)/SiNx to overcome the insulating nature of SiO2 by taking advantage of the reduced bandgap in SiNx. Using SiNx as the host matrix favors the electrical conductivity of carriers * Correspondence: [email protected] CIMAP UMR CNRS/CEA/ENSICAEN/UCBN, 6 Bd. Maréchal Juin, 14050 Caen Cedex 4, France
while we still maintain the quantum confinement as done with the SiO2 matrix. This study aims at fabricating and comparing the light emission properties of three different kinds of multilayer compositions: (a) SRSO/ SiO 2 , (b) SRSO/SiN x , (c) SiN x /SiO 2 . Such a study is important to understand the influence of host matrices on the Si-nc and consequently to achieve an optimized solar cell device in the future.
Experimental details Three kinds of multilayer structures were fabricated on 2” Si wafer by reactive magnetron sputtering comprising 50 patterns
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