Optical and electrical modeling of thin-film silicon solar cells
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Optical and electrical modeling of thin-film silicon solar cells M. Zemana) Delft University of Technology–Delft Institute of Microsystems and Nanoelectronics (DIMES), 2600 GB Delft, The Netherlands
J. Krc University of Ljubljana, Faculty of Electrical Engineering, 1000 Ljubljana, Slovenia (Received 22 August 2007; accepted 28 December 2007)
This article focuses on the modeling and simulation of thin-film silicon solar cells to obtain increased efficiency. Computer simulations were used to study the performance limits of tandem and triple-junction, silicon-based solar cells. For the analysis, the optical simulator SunShine, which was developed at Ljubljana University, and the optoelectrical simulator ASA, which was developed at Delft University of Technology, were used. After calibration with realistic optical and electrical parameters, we used these simulators to study the scattering properties required, the absorption in nonactive layers, antireflective coatings, and the crucial role of the wavelength-selective intermediate reflector on the performance of the solar cells. Careful current matching was carried out to explore whether a high photocurrent [i.e., more than 15 mA/cm2 for a tandem hydrogenated amorphous silicon (a-Si:H)/hydrogenated microcrystalline silicon (c-Si:H) solar cell and 11 mA/cm2 for a triple-junction a-Si:H/amorphous silicon germanium (a-SiGe:H)/c-Si:H solar cell] could be obtained. In simulations, the extraction of the charge carriers, the open-circuit voltage, and the fill factor of these solar cells were improved by optimizing the electrical properties of the layers and the interfaces: a p-doped, a-SiC layer with a larger band gap (EG > 2 eV) and buffer layers at p/i interfaces were used. Simulations demonstrated that a-Si:H/c-Si:H solar cells could be obtained with a conversion efficiency of 15% or higher, and triple-junction a-Si:H/a-SiGe:H/c-Si:H solar cells with an efficiency of 17%. I. INTRODUCTION
Worldwide, numerical simulation of the optical and electrical behavior of semiconductor devices is an established method for improving existing devices, obtaining insight into their physical operation, and developing new devices. A number of sophisticated semiconductor device-simulation packages are already commercially available on the market such as Atlas from SILVACO1 Data Systems Inc. (Santa Clara, CA), Crosslight Software Inc.2 (Vancouver, Canada), and Synopsis Inc.3 (San Jose, CA). These programs have primarily been designed for two-dimensional (2D) modeling of a wide range of crystalline semiconductor devices, but gradually they have been extended to include the possible modeling of polycrystalline and amorphous semiconductor-based dea)
Address all correspondence to this author. e-mail: [email protected] This paper was selected as the Outstanding Symposium Paper for the 2007 MRS Spring Meeting Symposium A Proceedings, Vol. 989. DOI: 10.1557/JMR.2008.0125 J. Mater. Res., Vol. 23, No. 4, Apr 2008
vices such as thin-film transistors and solar cells. The advantage of th
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