Phenoxazine or Phenothiazine: From Heteroatom Substitution to Conformational Change and Interfacial Effects of π-Conjugated Ligands in 2D/3D Perovskite Solar Cells

Abstract Utilizing π-conjugated ligands offers opportunities to ameliorate intermolecular interactions between spacer cations, improving charge transport in 2D perovskites. We develop two new ligands by incorporating phenoxazine (PXZ) or phenothiazine (PTZ) moieties, namely PXZEAI and PTZEAI, in which oxygen-to-sulfur substitution induces the intrinsically coupled effects of a more folded conformation (17° smaller dihedral angle) and interfacial chemistry. Unexpectedly, X-ray diffraction (XRD) analysis exhibits distinct lattice spacings in (PTZEA)2PbI4 (16.81 Å) and (PXZEA)2PbI4 (20.36 Å). Density functional theory simulations and synchrotron radiation single-crystal XRD reveal closer packing for (PTZEA)2PbI4, consistent with stronger intermolecular π–π interaction enabled by a more folded conformation, together with sulfur-specific interfacial effects. Grazing incidence wide-angle X-ray scattering results further support π–π interactions between PTZEA+ cations. Ultimately, a contrasting efficiency trend is observed in 2D/3D perovskite solar cells (PTZEAI (25.28%) > control (23.18%) > PXZEAI (19.08%)). This performance difference reflects the synergy of heteroatom-driven conformational change and sulfur-mediated interfacial effects.