Laminated fabrication of polymeric photovoltaic diodes

Photoexcited electron transfer between donor and acceptor molecular semiconductors provides a method of efficient charge generation following photoabsorption, which can be exploited in photovoltaic diodes1,2,3. But efficient charge separation and transport to collection electrodes is problematic, because the absorbed photons must be close to the donor–acceptor heterojunction, while at the same time good connectivity of the donor and acceptor materials to their respective electrodes is required. Mixtures of acceptor and donor semiconducting polymers3,4 (or macromolecules5) can provide phase-separated structures which go some way to meeting this requirement, providing high photoconductive efficiencies. Here we describe two-layer polymer diodes, fabricated by a lamination technique followed by controlled annealing. The resulting structures provide good connectivity to the collection electrodes, and we achieve a short-circuit photovoltaic quantum efficiency of up to 29% at optimum wavelength, and an overall power conversion efficiency of 1.9% under a simulated solar spectrum. Given the convenience of polymer processing, these results indicate a promising avenue towards practical applications for such devices.