Insights into the Structural-Transport Property Relationship of the Size-Dependent Organic Molecules on Metal Surfaces

Organic semiconductors are pivotal for emerging flexible displays, large-area electronics, and low-cost photovoltaics, where device performance crucially hinges on energy-level alignment at metal/organic interfaces. However, the vast molecular and substrate design space hinders the development of predictive interface design rules. Here, we systematically investigate the adsorption and charge transport of size-dependent aromatic molecules across six transition metal surfaces with density functional theory (DFT) calculations. The interfacial interactions govern two distinct regimes: physisorption and chemisorption. Expanding molecular size drives a transition toward strong chemisorption, enhancing electronic coupling and charge transfer, which intensifies Fermi-level pinning and lowers the slope of Schottky barrier heights versus metal work functions. Moreover, using non-equilibrium Green’s function (NEGF) simulations, we formulate the interfacial descriptor, T, that integrates both the Schottky barrier height and tunneling barrier width. Remarkably, this descriptor correlates exponentially with device output current, achieving >90% predictive accuracy and significantly outperforming conventional Schottky models. This relationship remains robust upon heteroatom incorporation, demonstrating broad universality across diverse molecular electronic architectures.