DOPED AND ENCAPSULATED FLUORESCENT PEROVSKITE NANOMATERIALS AND THE PHOTOPHYSICAL PROPERTIES OF THEIR NANOCOMPOSITES

Abstract

The thesis entitled “DOPED AND ENCAPSULATED FLUORESCENT PEROVSKITE NANOMATERIALS AND THE PHOTOPHYSICAL PROPERTIES OF THEIR NANOCOMPOSITES” has been divided into Six chapters, Chapter 1 This chapter comprises a concise review of the synthesis of metal lead halide perovskite nanocrystals (PNCs) and their applications in different optoelectronic devices. This chapter also covered the history of nanotechnology and nanoscience. The different optical properties of perovskite such as absorption and emission, exciton binding energy, and quantum confinement are discussed. The HOIP nanoparticles show charge transfer and energy transfer properties with several acceptor molecules. All the section provides the objective and challenges of their field as well as the background of research work. Chapter 2 This chapter is divided into two sections. i.e. Section 2A and Section 2B. Section 2A In this section, we have synthesized the Pb-doped Mn-based: CH3NH3Mn1-xPbxBr3-yCly microcrystals. The perovskite nanoparticles got much attention in research due to their interesting optoelectronic properties. The true potential application of lead-based perovskite nanoparticles has been hampered due to their toxicity and stability. This chapter demonstrated a green approach for toxicity removal of lead halide perovskites to resolve their toxicological aspects using manganese-based metal halide microcrystals. Pb doped Mn-based: CH3NH3Mn1-xPbxBr3-yCly microcrystals show better stability in solid-phase over solution phase with an absolute photoluminescent quantum yield [PLQY] of 30%. All characterization has been done using ultraviolet, photoluminescence, infrared spectra, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, and thermogravimetric analysis Section 2B In this section, we demonstrated the synthesis of Ni-substituted cesium lead bromide (CsPbBr3) PNCs at room temperature. The synthesis process is accomplished without using any sort of protection and the enhancement in emission property is analyzed by the Photoluminescence (PL) Spectra and Absolute Photoluminescence Quantum Yield (PLQY) value. It is investigated that as the Ni element replaces the lead metal ion, a blue shift is recorded in PL spectra. The Ni-substituted PNCs exhibit a longer lifetime than pristine-CsPbBr3 and were analyzed by the time-correlated single-photon (TCSPC) analysis. The introduction of divalent elements serves as a defect in the perovskite framework, reducing the recombination rate of holes and electrons. The green fluorescence obtained from the Ni- substituted CsPbBr3 perovskites nanocrystals plotted on CIE 1931 depicts the high color purity. The fluorescence intensity and XRD pattern remains consistent even after storage for several months. Furthermore, the change in morphology has been explored by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) images. Chapter 3 This chapter comprises the tunability in the emission of perovskite nanocrystals with different sizes of TiO2 from nano to microspheres. Organic-inorganic methylammonium lead halide PNCs have emerged as excellent materials for device fabrications. But due to the lack of long-term stability of PNCs, their applications have been hampered in commerciality. The green luminescent CH3NH3PbBr3 nanocrystals have been prepared by ligand assisted reprecipitation (LARP) method, which proclaims a photoluminescent quantum yield (PLQY) of 43%. The optical properties of synthesized perovskite nanocrystals have been recorded with different sizes of TiO2. It is investigated that these perovskite nanocrystals (PNC) show quenching of photoluminescence with PLQY of 32% after sonication with nano TiO2 (n-TiO2), due to the higher surface of n-TiO2. This reduces the recombination rate and improve the electron transfer from PNC to n-TiO2. The quenching phenomenon is also depicted by the study of electrochemical measurement. However, its encapsulation into the pores of TiO2 microspheres (m-TiO2) remarkably enhances the PLQY to 95%. Moreover, the enhancement of stability was also observed in the latter case. Furthermore, the encapsulation of perovskite nanocrystals was examined by transmission electron microscopy (TEM) and nitrogen adsorption-desorption isotherm analysis. Chapter 4 In this chapter, the charge transfer study from the excited state of MAPbBr3 PNC to molybdenum disulfide (MoS2) in chloroform solution is investigated using a fluorescence approach. Due to their exceptional properties and distinctive structures, transition metal dichalcogenides (TMDs) are promising materials for optoelectronic devices. In this study, we have combined hybrid organic inorganic perovskite nanocrystals MAPbBr3 with MoS2 solution. A significant electron transfer from MAPbBr3 to MoS2 has been depicted by photoluminescence (PL) spectra, time-correlated single photon count (TCSPC), transient absorption spectroscopy (TAS), and shortening of the absolute PL quantum yield (PLQY) of hybrid MAPbBr3/MoS2 nanocomposites. Fluorescence quenching of perovskite nanocrystals has shown an increase in quenching efficiency. The photoexcited charge transfer from MAPbBr3 to adjacent MoS2 is further correlated using electrochemical tests that compare reduction and oxidation potential. e e h+ The results revealed that the MoS2 extracts the charge from the excited state of PNCs. This work demonstrates the charge transfer behaviour of hybrid halide perovskites with two-dimensional TMDs materials and a combination of these materials could help us to understand the actual potency of MAPbBr3 PNCs in their real applications. Chapter 5 This chapter is divided into two sections. i.e. sections 5A and 5B. Section 5A This section presents the efficient charge transfers from methylammonium lead halide, MAPbX3 (X = Br, I) PNCs to 5, 10, 15, 20-tetraphenylporphyrin (TPP) molecules are investigated in detail. Photoluminescence (PL) spectroscopy and absolute quantum yield measurement were used to This efficient fluorescence quenching leads to an increment in quenching efficiency value. evaluate fluorescence quenching. The quenching of fluorescence intensity is not attributed to the change in a lifetime as investigated by time-correlated single-photon counting (TCSPC) measurement, suggesting static electron transfer from PNCs to TPP molecules. Such static fluorescence quenching corresponds to the adsorption of TPP onto the surface of hydrophobic PNCs and is examined via TEM images. The cyclic voltammetry (CV) studies were used to compare PNCs and PNCs@TPP nanocomposites revealing that the electron transfer process occur from the electron donor PNCs to the organic acceptor TPP molecules. Section 5B PS-C@TPP In this section, the light-harvesting properties of methylammonium lead bromide (CH3NH3PbBr3) PNCs using β-octatriphenylamino-5,10,15,20-tetraphenylporphyrin (H2TPP(TPA)8) molecules as energy acceptor has been studied. The hybrid lead halide perovskite has created immense research interest due to low-cost materials utilized for photovoltaic devices, photodetectors, light-emitting diodes, sensors, and memory devices. Owing to the quantum confinement of perovskite nanocrystals displaying intense luminescence are suitable for most applications. Hydrophobically-capped CH3NH3PbBr3 PNCs show bright fluorescence in the solution medium. However, with H2TPP(TPA)8, the fluorescence intensity of PNCs was quenched, and efficient energy transfer occurred from PNCs to H2TPP(TPA)8. The PL spectroscopy and TCSPC measurements were utilized to analyze the quenching of fluorescence. These observations show the significant applications for perovskite-related light-harvesting devices and artificial photosynthesis system. In this chapter, the fullerene derivative such as [6,6]-phenyl C61 butyric acid methyl ester (PCBM) is employed as a highly potent alternative n-type material to study the charge transfer behavior of hydrophobically-capped CH3NH3PbBr3 perovskite nanocrystals (PNCs). The solution processed CH3NH3PbBr3 exhibited bright fluorescence in toluene, but it is quenched in the presence of PCBM corresponds to the electron transfer from the excited state of PNCs to PCBM. The PL spectroscopy, PLQY value, TCSPC analysis, and TAS approach were utilized to study the charge transfer process. The Stern-Volmer plot and TCSPC analysis were used to probe the interaction of PCBM with PNCs. The band alignment reveals that electron transfer from the excited state of PNCs to PCBM is thermodynamically allowed. These outcomes highlight the excited state interaction of CH3NH3PbBr3 PNCs and photocatalytic applications.