REFINED MODELING OF OPTICAL CONFINEMENT IN THIN SILICON LAYERS WITH ALAMBERTIAN BACK REFLECTOR FOR SOLAR-CELL APPLICATIONS

An attempt is made to assess the accuracy of the simplifying assumptio n 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 derive d for the absorption enhancement factor as a function of the refractiv e 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 a lso obtained and studied. More general problems involving realistic li ght trapping schemes and/or actual material properties are treated num erically, sometimes by means of a suitably modified ray-tracing comput er program. It turns out that the error in making the above-mentioned approximation is relatively minor if the layer has a Lambertian back-r eflector, whether its front surface is textured or not, but becomes mo re appreciable for a flat back-reflector particularly as its reflectan ce approaches unity. (C) 1998 American Institute of Physics.