Molecularly Resolved Electronic Landscapes of Differing Acceptor–Donor Interface Geometries

Organic semiconductors are a promising class of materials for numerous electronic and optoelectronic applications, including solar cells. However, these materials tend to be extremely sensitive to the local environment and surrounding molecular geometry, causing the energy levels near boundaries and interfaces essential to device function to differ from those of the bulk. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STM/STS) have the ability to examine both the structural and electronic properties of these interfaces on the molecular and submolecular scales. Here, we investigate the prototypical acceptor–donor system, 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA)/copper(II) phthalocyanine (CuPc) using submolecularly resolved pixel-by-pixel STS to demonstrate the importance of subtle changes in interface geometry of prototypical solar cell materials. PTCDA and CuPc were sequentially deposited on NaCl bilayers to create lateral heterojunctions that were decoupled from the...