Recombination processes in dye-sensitized solid-state solar cells with CuI as the hole collector

Construction of dye-sensitized solid-state solar cells requires identification of hole collectors and understanding of the dissipative processes that limit the energy conversion efficiency. One of the hole collectors fairly well studied and giving a reasonably high efficiency is CuI. In this note we show that stoichiometrically excess iodine molecules adsorbed at the CuI surface acts as hole trapping sites (located at similar to 0.2eV above the conduction band edge) that mediate recombination, affecting the performance of the cell. Fluorescence measurements reveal that exposure of CuI films to iodine vapor generates surface traps and as iodine diffuses to the bulk, surface trap density is greatly reduced. Methods by which the recombination originating from this effect may be circumvented are also discussed. (C) 2003 Elsevier B.V. All rights reserved.