Solar Energy Materials and Solar Cells Donor-acceptor pairs to limit Voc-improvement of photo-diodes

When deep-level centers are inserted near the junction interface, the open-circuit voltage of photo-diodes i reduced. The performance degradation due to the doped layer is sensitively position-dependent; its maximum effect is at a position where n---p, for similar recombination rates of electrons and holes. In high-efficient solar cells, it is suggested that donor-acceptor pairs that are created by the conventional diffusion process are responsible for the unintentional limitation of the open-circuit voltage. Computation of the solution curves of transport-, continuity-, and Poisson equations for a two-carrier model indicate that the omission of close pairs by insertion of a thin undoped layer (inverse delta-doping), and consequential reduction in the density of distant pairs causes an increase of the open-circuit voltage and fill factor without concomitant decrease of the short-circuit current. I