Enhanced p-type work function tunability induced by electrostatic molecular alignment and surface coverage in conjugated small-molecule electrolyte

Here, we report that a chemically p-doped conjugated small-molecule electrolyte (CSE) can be used as a strong and uniform dipole array for highly efficient optoelectronic devices via electrostatically induced molecular alignment and surface coverage on metal electrodes. Based on the structural and electrical characterization as well as evaluation of the surface potential, we confirm a close structure-property relationship in the p-doped CSE; the CSE molecules can interact electrostatically with each other and with the metal surface, leading to an out-of-plane orientation and full surface coverage, respectively, providing a superior WF tunability compared to that of its polymeric counterpart. Our results clearly indicate that the overall strength of the electric dipoles in the thin-film interfacial layer can be controlled by the degree of molecular alignment and coverage, making this material broadly applicable in highly efficient optoelectronics.