Refined modeling of optical confinement in thin silicon layers with a Lambertian back reflector for solar cell applications

An attempt is made to assess the accuracy of the simplifying assumption of total transmission (total loss) of the light inside the "loss" or "escape" cone which is made in many models of optical confinement in thin-layer silicon solar cells. A closed form expression is derived for the absorption enhancement factor as a function of the refractive index in the low-absorption limit for a thin layer with a Lambertian back-reflector and is compared with the expression derived previously on the basis of the "total loss" assumption. The generation profile, needed for the evaluation of solar cell performance parameters, is also obtained and studied. More general problems involving realistic light trapping schemes and/or actual material properties are treated numerically, sometimes by means of a suitably modified ray-tracing computer program. It turns out that the error in making the above-mentioned approximation is relatively minor if the layer has a Lambertian back-reflector, whether its front surface is textured or not, but becomes more appreciable for a flat back-reflector particularly as its reflectance approaches unity. (C) 1998 American Institute of Physics.