A NEW DOUBLE CARRIER ANALYTICAL MODEL OF CARRIERS TRANSPORT IN P-I-N AMORPHOUS-SILICON SOLAR-CELLS

A new analytical method has been developed to investigate the transport problem in a-Si p-i-n solar cells. The model is an actual improvement of the "variable minority carrier" model by Okamoto et al. In fact, compared to the Okamoto model, it has the following characteristics: (a) it takes into account both the majority and the minority carriers and currents in the whole structure; (b) photocarrier generation is analytically treated as a non-homogeneous term; and (c) exact boundaries conditions are applied to carriers and currents at the interfaces, i.e. physical continuity of the majority and minority carriers and current distributions at the two interfaces with the doped regions, and at the "variable minority carrier" interface in the intrinsic zone. This improved description has the peculiarities of a quick calculation and easy physical comprehension of an analytical solution, but it also allows one to obtain a more precise analysis of the measurable quantities, particularly around the open circuit voltage point, where effects due to the majority carriers are considerable. Examples of the dark cell electrical behaviour as a separate function of carrier lifetimes and mobilities are finally discussed.