Mixed phase silicon oxide layers for thin-film silicon solar cells
- PDF / 305,152 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 77 Downloads / 199 Views
Mixed phase silicon oxide layers for thin-film silicon solar cells Peter Cuony1, Duncan T.L. Alexander2, Linus Löfgren1, Michael Krumrey3, Michael Marending1, Mathieu Despeisse1, Christophe Ballif1 1
Ecole Polytechnique Fédérale de Lausanne (EPFL), Institute of Microengineering (IMT), Photovoltaics and Thin Film Electronics Laboratory (PV-Lab), Rue Breguet 2, 2000 Neuchâtel, Switzerland
2
Ecole Polytechnique Fédérale de Lausanne (EPFL), Interdisciplinary Centre for Electron Microscopy (CIME), 1015 Lausanne, Switzerland
3
Physikalisch-Technische Bundesanstalt (PTB), Abbestr. 2-12, 10587 Berlin, Germany
ABSTRACT Lower absorption, lower refractive index and tunable resistance are three advantages of doped silicon oxide containing nanocrystalline silicon grains (nc-SiOx) compared to doped microcrystalline silicon, for the use as p- and n-type layers in thin-film silicon solar cells. In this study we show how optical, electrical and microstructural properties of nc-SiOx layers depend on precursor gas ratios and we propose a growth model to explain the phase separation in such films into Si-rich and O-rich regions as visualized by energy-filtered transmission electron microscopy. INTRODUCTION The tandem configuration with a hydrogenated amorphous silicon (a-Si) top cell and a hydrogenated microcrystalline silicon (μc-Si) bottom cell, also called the Micromorph configuration is a promising candidate for future large scale deployment of photovoltaics for electricity generation due to abundant source materials and scalable and low-cost deposition processes. Hydrogenated silicon oxide containing nanocrystalline silicon grains (nc-SiOx) has attracted much interest in the last years because of different applications in thin-film silicon solar cells: First, p-type nc-SiOx is an excellent window and anti-reflection layer, due to lower absorption coefficient and lower refractive index when compared to p-type μc-Si layers [1]. Second, n-type nc-SiOx can be used as intermediate reflecting layer, when inserted between two sub-cells of a tandem configuration, allowing for advanced light-trapping schemes [2-5]. Third, tunable resistance of p- and n-type nc-SiOx can help to reduce the impacts of shunts on the electrical cell parameters [1, 6]. EXPERIMENTAL DETAILS The nc-SiOx layers are deposited at 200 °C from a gas mixture of SiH4, H2, and CO2 by plasma enhanced chemical vapor deposition, and p- and n-type doping is achieved by adding B(CH3)3 and PH3, respectively. Fourier Transform Infrared (FTIR) absorption measurements are performed with a Nicolet 8700 system from Thermo on samples deposited on silicon wafers and absorption spectra are normalized with the layer thickness. Rutherford backscattering (RBS) and hydrogen forward scattering (HFS) measurements to determine Si, O, and H contents are carried
349
out by the Evans Analytical Group. The density is deduced from X-ray reflectometry performed with synchrotron radiation at the PTB four-crystal monochromator beamline at BESSY II [7]. The absorption coefficient (Į) and refr
Data Loading...
