An optoelectronic device comprises electon donor D and acceptor A semiconducting species and an intervening co-oligomeric or copolymeric species provided to alter the energy transfer characteristics of excitons to or from the interface between the said electron acceptor and donor species. The intervening species may be of the form Am-Xn-Do, where m, n and o are each 0 or a positive integer and at least two of A, X and D are present.