Organic photodetectors based on graded heterostructure of donor and acceptor layers

We have fabricated and characterized photodetectors based on organic semiconductors. Concentration gradients of an electron-donor and an electron-acceptor were achieved between the two electrodes. Such gradients in the molecular scale, introduced via layer-by-layer electrostatic assembly, provided an extended region for exciton dissociation and bicontinuous pathways for carrier transport to the opposite electrodes. Results in the graded heterostructures have been compared with bulk-heterojunction devices.