Nanoscale mapping of photo-induced charge carriers generated at interfaces of a donor/acceptor 2D-assembly by light-assisted- scanning tunneling microscopy

Abstract : We have investigated charge transfers between donor (D) and acceptor (A) species at their excited state in a light-assisted STM setup (LA-STM). Through an all-solution process, we have elaborated supramolecular architectures deposited on the Au(111) sur- face and made of 2D islands of PC71BM (electron acceptor) on top of a single layer of the polymer PTB7 (electron donor). The STM junction under modulated laser irradiation exhibits a strong background of photothermal signal attributed both to vertical and lateral expansion of the tip. However, from the analysis of di↵erential images obtained at opposite voltages, we have been able to detect additional photocurrent peaks located at the PTB7/PC71BM interfaces, providing evidence for active charge transfer be- tween D/A species at their excited state. We discuss this phenomenon in the framework of a charge transport model at interfaces in organic electronics systems.