Donor/acceptor type photodetectors: role of substitution in acceptor material

Abstract

We report fabrication and characterization of photodetectors based on organic semiconductors. Single and multiple heterostructures between electron donor and acceptor materials are used. Moreover, by varying the substitutes of the acceptor molecule, five different donor/acceptor combinations are presented. Photocurrent depends on the choice of the acceptor material, showing importance of energy mismatch between lowest unoccupied molecular orbital (and highest occupied molecular orbital) levels of donor and acceptor molecules. Additionally, the photocurrent also depends on the number of donor/acceptor interfaces. The results can be explained in terms of an energy band diagram of the devices. From the impedance spectroscopy, we show that the change in dielectric constant of the active material due to illumination has a direct relevance to the external current of the photodetectors.