Nanoscale Mapping of Photo‐Induced Charge Carriers Generated at Interfaces of a Donor/Acceptor 2D‐Assembly by Light‐Assisted‐Scanning Tunneling Microscopy

Abstract Charge transfers between donor (D) and acceptor (A) species at their excited state in a light‐assisted STM setup (LA‐STM) are investigated. Through an all‐solution process, supramolecular architectures deposited on the Au(111) surface and made of 2D islands of PC₇₁BM (electron acceptor) on top of a single layer of the polymer PTB7 (electron donor) are elaborated. 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 differential images obtained at opposite voltages, additional photocurrent peaks located at the PTB7/PC₇₁BM interfaces are detected, providing evidence for active charge transfer between D/A species at their excited state. This phenomenon is discussed in the framework of a charge transport model at interfaces in organic electronics systems.