Photon Recycling and Efficiency Limit of a Silicon Solar Cell With a Specular and a Diffusive Surface

Analytical expressions for photon reabsorption probability in a solar cell, in which one of the surfaces, front or back, is specular and the other one is diffusive are obtained within the ray optics approximation. Due to the free carrier absorption, the light-generated current and the radiative recombination coefficient depend on the electron-hole pair density within the cell. Accurate analytical approximations that describe this effect are derived. These formulae are applied to evaluate the limit efficiency of a c-Si solar cells, whose one surface is specular and the other is diffusive, under AM1.5G irradiation at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ 25\,^{\circ }$</tex-math></inline-formula>C. For the solar cells with specular front and diffusive back surfaces, the efficiency is maximized at the cell thickness of 110 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m and has a value of 29.4%. In the configuration with diffusive front surface, the limiting efficiency of 29.5% is achieved at the optimal thickness of 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m regardless of the texturing type of the back surface.