Design, Synthesis, and Characterization of 2D halide Perovskite Lateral heterojunctions

In this thesis, 2D layered halide perovskite lateral heterojunctions have been designed, fabricated, and characterized from several aspects. Initially, the formation of lateral heterostructures between halides was investigated using two solution-based strategies: anion exchange (Chapter III) and direct formation via a solvation-crystallization approach (Chapter IV). Based on differences in solubility and recrystallization, triple-halide and dual metal-based heterostructures comprising chloride-, bromide-, and iodide-based 2D layered perovskites and Pb- and AgBi-based metals, respectively, are designed, fabricated, and investigated. In Chapter III, a scalable, facile, solution-based method for the synthesis of 2D layered perovskite in-plane heterostructures was evaluated. After evaluating the structural and optical properties of the heterostructures, it was found that, in bromide-to-iodide exchange structures, core-frame heterostructures form via solvation and recrystallization. In contrast, iodide-to-bromide heterostructures exhibit a different mechanism: the formation of multiple alloyed phases has been used to confirm the vacancy-assisted anion-exchange process. This leads to preferential occupation of the halide sites in the octahedral lattice of 2D layered perovskites. Therefore, the solution-based exchange process is more complex than in 3D perovskites because the preferential occupation of distinct octahedral sites is explicitly accounted for. In Chapter IV, an innovative fabrication method is introduced to produce 2D layered perovskite lateral heterostructures via antisolvent-triggered recrystallization, offering a low-cost, flexible design and fabrication technique. The composition of the heterostructures was controlled by the concentrations of dissolved materials in the growth solution, thereby enabling band-gap tuning and associated interfacial offsets, tailoring emission colors, charge transfer, and recombination dynamics at the junction. Sharp interfaces can be achieved by sequentially injecting different 2D-layered perovskites, thereby tailoring the material sequence of the heterostructures; this approach can be extended to multiple heterojunctions. The method provides a versatile platform for designing and fabricating heterostructures with tunable band gaps and electric potential landscapes in perovskite materials, which could be of interest for optoelectronic applications.