Optical and electrical modeling of thin-film silicon solar cells

Abstract

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 (μc-Si:H) solar cell and 11 mA/cm2 for a triple-junction a-Si:H/amorphous silicon germanium (a-SiGe:H)/μc-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/μc-Si:H solar cells could be obtained with a conversion efficiency of 15% or higher, and triple-junction a-Si:H/a-SiGe:H/μc-Si:H solar cells with an efficiency of 17%.