Molecular p-n Junction Photodiodes of Langmuir Multilayer Semiconductors

The electrical and photoelectric characteristics of Langmuir-Blodgett film heterojunctions have been studied using organic p-n diodes consisting of monolayers of four kinds of merocyanine (MX) dyes stacked on monolayers of distearyl paraquat (PQ). A rectifying effect observed in the dark indicates that the PQ and MX monolayers act as n-type and p-type regions, respectively. The photocarriers are identified as electrons generated in the photosensitive MX monolayers. Comparison between different types of MX dyes suggests that laterial motion of carriers occurs in the p-n junctions, and that the acceptor nuclei, i.e., rhodanine in MX, play a dominant role in determining the diffusion potential with respect to the PQ n-type region.