Perimeter recombination in thin film solar cells

Abstract

Surface recombination has a profound effect on the performance of a solar cell, at the illuminated surface reduces its photocurrent and along the cell's perimeter increases its dark current. The perimeter recombination current has two components; the first is due to recombination at the surface that intersects the space-charge layer while the second originates from recombination at the surface of quasi-neutral regions. The current due to recombination at the depleted layer surface is treated in a similar way to that of the bulk, using a simple model. We present an analytical form that produces results that agree well with reported experimental findings. The recombination current outside the space-charge region is of two-dimensional nature, it represents lateral diffusion of minority carriers from the boundary of the depleted layer to the perimeter. This current is calculated by solving numerically a two-dimensional continuity equation. As the ratio of perimeter to area is increased the perimeter current acquires important proportions, consequently the expected bulk recombination current becomes insignificant.