Transfer of charges across the interface between an organic semiconductor and an optically transparent, conductive oxide (TCO) electrode, such as indium-tin oxide (ITO), is a fundamental process in the operation of organic solar cells (OSCs) and organic light-emitting diodes (OLEDs).
Efforts to improve the efficiency of interfacial charge transfer in OSCs and OLEDs have focused on tuning TCO surface properties via adsorption of an organic monolayer that serves as a "mediator." In a recent paper in the journal ACS Advanced Materials and Interfaces, Dr. Yilong Zheng (front row, 2nd from right), a 2016 PhD graduate from the Saavedra lab, showed how the rate of charge transfer between a single monolayer of perylene diimide (PDI) molecules and an ITO electrode can be tuned by varying the degree of intermolecular interactions between the PDIs. A series of PDIs bearing a varying number of bulky substituents was synthesized by collaborators at the Georgia Institute of Technology. When adsorbed to ITO, PDI molecules with fewer bulky substituents exhibited a higher degree of intermolecular interactions and more rapid charge transfer at the electrode, an effect attributed to lateral exchange of charges between adsorbed PDIs. Overall, these results provide guidance for ongoing development of adsorbates designed to facilitate charge transfer at TCO electrodes in organic electronic devices.
Photo and graphic courtesy of S. Scott Saavedra. Read the full article.