Synthetic control in low dimensional 'Pb' and 'Pb-free' perovskites for rationalizing the origin of their luminescence properties

Abstract

Perovskite materials has gathered a huge attention due to their enabling properties and optoelectronic applications. Perovskites in low dimension show highly tunable optical properties and this could be advantageous for light emitting devices. This thesis shows a purely corner connected 1D structure, with 9% PLQY, and further optical tuning was exhibited by changing the halide compositions. In addition, it sheds light on the importance of connectivity vs. broadband self-trapped emission and found that they were weakly correlated. In contrast, besides connectivity, factors like nature of halide, nature of the ligand, geometry (flat or contorted) will play a decisive role in directing the photoluminescence property. Apart from lead-based perovskite, this thesis explored various ‘lead-free’ systems, composed of antimony and tellurium. To validate the correlation of structure-property, a variety of antimony-based zero-dimensional emitting pervoskite were synthesized utilizing a common organic templating ligand by varying the temperature and ligand concentration. Study indicates that the extent of distortion is well correlated with the variable PLQY, emission wavelength, and Stokes shift within the structures. This thesis also investigated a tellurium-based zero-dimensional structure, and the structure has shown a strong room temperature luminescent broadband emission with 15% PLQY. A down-conversion LED was fabricated using the tellurium-based perovskite aimed to utilize its visible light excitonic absorption at 445 nm. Doping is a well-proven strategy to tune the optical property further. Since low dimensional perovskite possesses a high exciton binding energy (>150 meV), it is suitable for a host to dopant energy transfer. This thesis shows a successful substitutional doping of Mn2+ ion in lead bromide-based 2D perovskite utilizing mechanochemical grinding metholodogy and observed > 24% PLQY across all dopant concentrations. The discussed method of doping is scalable and can be potentially applied for large-scale practical applications.