FLUORESCENT METAL HYBRID NANO-PEROVSKITE: SYNTHESIS AND APPLICATIONS

Abstract

Metal hybrid halide perovskite semiconductor nanocrystals came into limelight from 2014. The thesis entitled "Fluorescent Metal Hybrid Nano-perovskite: Synthesis and Applications" has been divided into five chapters: Chapter 1 presents a general introduction about motivation of fluorescent materials and era of nanoscience and nanotechnology. Starting point of research towards perovskite nanocrystals to development of materials along with various applications including solar cells, photodetectors, light emitting diodes are explianed in the introductory part. Detailed properties and applications of perovskite nanocrystals are mentioned to investigate the real problems in this field and formulation of problems was investigated accordingly. Thesis goal brief about the structural work, importance and methodogy. Chapter 2 describes the tunability in the optical properties of perovskite nanocrystals leads to tailoring of the morphology as well as the functionality of perovskite-based devices. In this chapter, we report a new approach in which fine tunability in optical studies has been observed in samples P1 to P9 by systematic physical mixing of already prepared CH3NH3PbI3 and CH3NH3PbBr3 nanoparticles. CH3NH3PbI3 and CH3NH3PbBr3 have been synthesized in the presence of excess ligands, due to which the visible and fluorescence peaks are blue shifted. Later, we observed tunability in the fluorescence peaks of samples P1 to P9 covering the visible region from 450–600 nm. Morphological studies of all the samples have been performed using XRD, TEM and AFM analysis. XRD studies reveal that the phase changes from cubic to tetragonal on moving from sample P1 to P9 and the TEM morphology reveals the self-assembled spherical structures of all samples.Chapter 3 describes about stability of CH3NH3PbBr3 perovskite nanocrystals by encapsulation in silica gel G and investigating bidentate ligand as succinic acid. This chapter is divided into two sections Section A and Section B. Section A demonstrated a facile method to grow organometal halide perovskite quantum dots in a solid silica matrix. The photoluminescence measurements of the MAPbBr3 quantum dots and corresponding large particles show a shift from blue to green emission with morphological changes. The nanocrystals impregnated on the silica matrix improve the stability and may be useful as functional materials in all solid state light emitting devices.In Section B we synthesized CH3NH3PbBr3 nanoparticles using succinic acid and oleylamine at a fixed ratio as ligands. The formed stable CH3NH3PbBr3 NCs exhibit narrow green photoluminescence with high quantum yield as compared to the perovskites formed through oleic acid. Moreover, a fluorescent keypad lock security device authorizing password entries was constructed based on the output emission signal. The fluorescent keypad lock could be unlocked upon entering the correct sequence of password, i.e. MPDSOC. Furthermore, characterizations and morphology studies have been performed using UV, PL, XRD, TCSPC and TEM. In addition, stability tests were monitored using fluorescence spectra.Chapter 4 deals with ultralong micro-belts of MAPbI3. It show bright and stable fluorescence in solution. Luminescent perovskites have been synthesized through centrifugation of solution processed with ligand assisted reprecipitation technique (LARP). All the electron spectroscopic analysis are evidenced for stacking of nanocrystals as bundles of self assembled micro-belts. Under an applied bias, migration of free charge carriers through long axis is feasible. This long micro-belts are found as promising channel material for two electrode nanodevices for good electrical conductivity.Chapter 5 deals with charge transfer studies between perovskite nanocrsytals with rhodamine dye B and carbon nanotubes. This chapter is also divided into two sections i.e. Section A and Section B.Section A deal with facile synthesis of tunable blue to green luminescent colloidal MAPbBr3 Perovskite NCs is synthesized by solution processed ligand assisted re-precipitation technique (LARP). Different behaviour in optical properties and morphology of MAPbBr3 perovskite NCs has been observed by tuning the ratio of oleic acid and oleylamine. Rhodamine B has been chosen as dye to study electron migration between perovskite NCs and dye. It has been investigated that both blue and green luminescent nanoparticles leads to different energy transfer behaviour with dye. Green luminescent MAPbBr3 nanoparticles are able to show Förster Resonance Energy Transfer whereas in blue luminescent nanoparticles, there is fluorescence quenching because of aggregation between perovskite and rhodamine b dye. These studies have been utilized in study of different interaction between tunable perovskite and rhodamine B dye.Section B deals with charge transfer study between lead halide-based perovskite nanocrystals and single walled carbon nanotubes (PNC@CNT nanocomposite) was performed. Solution processed MAPbX3 PNCs were very bright in luminescence but quenching happened with the presence of CNTs. This change is attributed to the electron transfer from PNCs to CNTs. The detailed change in fluorescence lifetime was investigated through time correlated single photon counting (TCSPC), suggesting mixed static and dynamic quenching along with decrease in lifetime. Morphological change was investigated by transmission electron microscopy (TEM) and it is attributed to the incorporation of PNCs on long CNTs. Also, PNC@CNT nanocomposite was explored for photoinduced current response which indicated ~3 fold increase in photoconductivity under light illumination (with a 1 mV bias). This electron transfer study between PNCs and CNTs helps in exploring charge dynamics.