Strategies for improving molecular donor-acceptor photocells: Selective doping and excitonic layers

The photon-exciton-charge carrier transformations in donor-acceptor (D-A) molecular photocells are discussed from a general viewpoint. The energy conversion efficiency of photocell is expressed phenomenologically as a product of the efficiencies of photon collection, excitonic interfacial dissociation, free carriers separation and collection at electrodes. Strategies to increase each step are suggested, which involves selective doping . In D(pD)-D-A-A(nA) structures, the selectively doped parts provide low serial resistance and create internal electric fields for the collection of charges, while in the undoped parts excitons are photogenerated. Ways to increase the effective use of absorbed photon energy and filling factor are suggested. Our recent experimental results on sensibilization by excitonic layer in D-M-A multilayered structures, and doping the D-layer by A molecules in D(A)/A cells are briefly discussed.