Light Trapping in Silicon Solar Cells Including Secondary Reflection on the Surrounding

We extend a commonly used analytical model of light trapping in silicon solar cells, which was introduced by Basore in 1993, by including secondary reflections on the surrounding. The extension enables more accurate measurements of bifacial solar cells by analytically decoupling the properties of the background (chuck) and the sample. The additional reflectance on a white background commonly accounts for an increase in short-circuit current density by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${0.5}\,{\text{mA/cm}^{2}}$</tex-math></inline-formula> compared with a nonreflective chuck. Also, the extension improves the accuracy of absorption profiles in optical solar cell models, and can further be employed to acquire additional information of simple reflectance measurements. The chuck extension is tested on reflectance measurements with black and white backgrounds, showing that the fitting procedure is more stable in comparison to a model without the extension, with the deviation of the parasitic absorption coefficient <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$A_\text{ppp}$</tex-math></inline-formula> being reduced from up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${30}{\%}$</tex-math></inline-formula> to less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${5}{\%}$</tex-math></inline-formula>. We also propose different sets of free parameters in the general Basore model framework, and evaluate some variants of this landscape regarding fit accuracy for different sets of measurement data. We find that most models require information on reflectance and transmittance to be well constrained. To meet the requirement, we propose reflectance measurements on black and white backgrounds to circumvent an additional transmittance measurement setup. Model fits to this dataset show good agreement with measured transmittance and absorptance spectra, with maximum deviations of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${4}{\%}$</tex-math></inline-formula> absolute within our samples.