Molecular Design of 2D Hybrid Halide Perovskites: Chirality, Intercalation and Doping

Abstract

This thesis explores novel strategies to design 2D layered hybrid perovskites (A₂MX₄; A: organic ammonium ion; M: Pb, Sn; and X: I, Br) by tailoring their nanoscale organic-inorganic interface for unique optoelectronic properties. These materials, with their natural quantum well structure comprising semiconducting inorganic (M-X) and insulating organic (A) layers, primarily exhibit properties governed by the M-X layer. However, the A-site ion presents an opportunity to induce advanced functionalities, such as chirality and bandgap tuning. In chapter 2, we introduce an idea to design chiral hybrid perovskites by using different conformers of chiral A-site ions. The gauche- and anti-conformers of 1-iodopropan-2-ammonium (IdPA) are alternatively arranged in (R-/S-IdPA)₂PbI₄. The anti-conformer of IdPA ion have significantly stronger electrostatic, hydrogen bonding, and halogen bonding interactions with the inorganic [PbI4]2- sublattice, compared to the gauche-conformer. This periodic asymmetry in non-covalent interactions induces helical chirality in (R-/S-IdPA)₂PbI₄. Another way to tailor the optoelectronic properties is by molecular intercalation through the labile organic sub-lattice. We intercalate hexafluorobenzene in phenethylammonium tin iodide [(PEA)2SnI4]. The intercalation increases the bandgap and suppresses the non-emissive states at cryogenic temperatures. Chapter 4 combines the exciton photophysics with the dopant states of Mn2+-doped butylammonium lead bromide [(BA)2PbBr4]. These approaches - conformer engineering, molecular intercalation, and lattice doping, successfully manipulated the organic-inorganic interface, demonstrating pathways to design chiral, emissive, and doped 2D perovskites.