Flatband solar cells: a model for solid-state nano-structured solar cells

Nano-structured solar cells are too complex for standard modeling. Here, we decouple the effects at a nm-scale from those at a /spl mu/m-scale. The 3D nano-porous geometry is simplified to a quasi-periodical nm-scale ordering of "unit cells" (a TiO/sub 2/ sphere and its p- semiconductor or dye/p-conductor shell). It is shown that, due to the periodical boundary conditions, such a unit cell is essentially field free; it is called here a "flatband cell\´". The band-diagram, including possible discontinuities, the Fermi levels, carrier density and recombination (interface and bulk) of these flatband cells is given accurately by a back-of-the-envelope calculation, as confirmed by numerical simulation. The unit cells are connected in a 1-D electrical network, which also accounts for the transport effects in the porous TiO/sub 2/ network and for the contact effects at the electrodes. Results for solid-state nano-structured cells are presented.