Theoretical Investigation on Pyrene-Based Self-Assembled Molecules Toward Efficient Interface Performance of...

Self-assembled monolayers (SAMs) provide a molecular platform for tuning electrode interfaces in perovskite solar cells (PSCs). To examine substituent effects in pyrene-derived phosphonic acids, we designed six derivatives of (2-(pyren-1-yl)ethyl)phosphonic acid (py3) and evaluated their gas-phase electronic structures, reorganization energies, predicted packing motifs, Marcus-Hush hopping descriptors, and adsorption on indium tin oxide (ITO) using density functional theory. Methyl and phenyl substitution increased the calculated intermolecular transfer integrals in the predicted packing models, whereas hydroxy substitution increased molecular polarity and reorganization energy. Adsorption calculations revealed substituent-dependent binding and charge redistribution on pristine and oxygen-deficient ITO. SAM/ITO DOS/PDOS analysis further showed that the near-Fermi electronic structure remains predominantly ITO-derived, while oxygen vacancies redistribute spectral weight on neighboring In atoms in a substituent- and energy-window-dependent manner. DOS/PDOS calculations for molecule/FAPbI₃(001) adsorption models also revealed distinct changes in near-Fermi spectral weight. Together, these calculations establish a multiscale structure-property picture linking molecular substitution to packing-mediated coupling, ITO adsorption, vacancy-sensitive electronic redistribution, and perovskite interfacial electronic structure. The resulting trends provide theoretical guidance for the design and experimental evaluation of pyrene-derived SAM molecules, while collective monolayer organization remains an additional factor in device operation.