Research Projects

Two-dimensional organic-inorganic halide perovskites, derived from the parent 3D perovskite ABX3 (where A = Cs+, CH3NH3+ [MA+], or HC(NH2)2+ [FA+]; B = Pb2+, Sn2+; and X = Cl−, Br− and I−), have garnered attention for optoelectronic and photovoltaic applications due to their structural tunability and favorable electronic properties. These quantum well-like structures comprise single or multiple layers of metal halide octahedra separated by bulky organic spacer cations. Based on the organic cation and stacking sequence, the 2D variants are classified as Ruddlesden-Popper (RP; A2An-1MnX3n+1), Dion-Jacobson (DJ; A″An−1MnX3n+1), and alternating cation interlayer (ACI; A″AnMnX3n+1) phases, where A′ and A″ are monovalent and divalent cations, respectively, and n denotes the number of octahedral layers. When the metal site contains mixed monovalent and trivalent cations, it yields hybrid layered double perovskites (HLDPs). These materials can be synthesized as single crystals via slow cooling or as nanocrystals and nanoplatelets (NPLs) using surfactants through hot-injection. At the nanoscale, the inorganic blocks form periodically stacked NPLs, producing lamellar architectures with distinct multilayer diffraction patterns, characteristic of superlattice formation. The flexible inorganic and organic sub-lattices can induce atomic-scale structural modulations with long-range order, disrupting the stacking uniformity and breaking local 3D translational symmetry, giving rise to a superstructure. These stacking faults, often overlooked, can promote higher-order n phases, unveiling a dimensional evolution from 2D layers to 3D NCs as n  . The structural coupling between inorganic slabs and organic barriers yields confined electronic states, with excitons primarily localized in the inorganic octahedral layers. Yet, structural inhomogeneities may cause leakage into the organic barriers. The packing and arrangement of octahedra strongly influence inter-well energy funneling across octahedra of varied n values. These systems exhibit temperature-dependent carrier injection, with each octahedral slab acting as an optical microcavity. At low temperatures, excitons are well-confined, producing distinct emission signatures, while at room temperature, enhanced exciton kinetic energy enables inter-well transfer and energy modulation. The emergent electronic coupling offers a unique structural route to tailor NPL superstructure optoelectronics. The novelty of the proposed work lies in introducing a new structural approach to engineer light-matter interactions in 2D NPL superstructures by harnessing the stacking faults as a tunable feature to control exciton leakage and the resultant energy modulation. To probe the temperature-driven atomic rearrangements, stacking faults and energy funneling across quantum wells, variable-temperature powder X-ray diffraction (XRD) will be employed. This approach will elucidate structural dynamics, phase transitions and symmetry changes in RP, DJ and HLDP systems. Rietveld refinement, electron microscopy, variable-temperature steady state optical characterization and ultrafast transient absorption spectroscopy (via collaboration) will complement the analysis. Supported by computational elucidation of thermo-excitonic dynamics, the acquired structural insights will guide the design of 2D hybrid halide photoabsorbers for bias-tunable and self-powered photodetectors, where performance depends on disorder-mediated carrier scattering, band gap shifts and recombination. The photodetectors will be tested from -30oC to room temperature. Understanding the modulated structures will unravel the roles of traps, defects and polarons in response time and noise characteristics. The synergistic structural-optical analysis will support dark current suppression, optimization of anisotropic charge transfer and control over emission shifts, ultimately improving the defect tolerance and operational stability at room temperature.