Designing low dimensional hybrid lead halide perovskites for excitonic photophysics chiroptics and water stability

Abstract

Three dimensional 3D lead halide perovskites like APbX3 A Cs CH3NH3 NH2CHNH2 X Cl Br I exhibit wonderful optoelectronic properties A bigger A site cation like butylammonium CH3 CH2 3NH3 disrupts the 3D octahedral network yielding lower dimensional perovskite inspired structures like two dimensional 2D layered perovskites A2PbX4 Unlike 3D perovskites the chemical compositions of low dimensional perovskites are not limited by the Goldschmidt tolerance factor Consequently it is possible to think of a large variety of organic and inorganic sub lattices Moreover the hybrid structure of these lower dimensional perovskites gives rise to various types of interactions This thesis explores the novel material design concepts the interactions in lower dimensional perovskites along with their optical properties More specifically i nature of quantum well structure in layered perovskites chapter 2 ii chemical insertions between Van der Waals layers chapter 3 iii chiral hybrid perovskites chapter 4 and iv water stable low dimensional perovskites chapter 5 have been addressed in this thesis Firstly we study 2D layered lead halide perovskite single crystals using optical absorption temperature dependent 10 K to 300 K photoluminescence and spatially resolved fluorescence microscopy imaging Surprisingly two excitonic absorption and emission features are observed The higher energy emission originates from individual Pb halide quantum well layers whereas the lower energy emission is assigned to the possible interaction between the adjacent Pb halide layers mainly through the layer edges Such assignments are verified by controlling the Pb halide inter layer interactions through molecular intercalation and varied chain length of organic cations Then we used chiral organic A site cations that induce chirality in inorganic Pb halide sub lattice and therefore showing excitonic circular dichroism The introduced chirality splits the emission states by lifting the spin degeneracy Moreover these chiral layered perovskites show high