Possibilities of creating photovoltaic devices using CuI/AgIn5S8 heterojunctions are considered. Among other properties, preferential formation of polar (111) surfaces makes n-type AgIn5S8 an attractive candidate for absorber layers of top cells in 4-terminal tandem structures. Cu-Ag exchange at the interface with p-type CuI was observed. This intermixing results in an additional component of Ag 3d5 photoelectron line after deposition of Cul, in the Cu (but not 1) contamination of the surface after a chemical removal of Cut, and in a photoelectric sensitivity of the junction at energies below the band gaps. Valence band offsets of 0.4 and 0.5 eV (cliff) were found at interfaces with thin film and bulk AgIn5S8, Supporting a conduction mechanism through interface recombination. Pinning conflict at the interface between materials with contradictory doping limitations is likely to promote the intermixing. (c) 2005 Elsevier B.V, All rights reserved.