Browsing by Author "Mohite, Aditya D"

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    Halide perovskites for high-efficiency and durable photovoltaics
    (2023-04-20) Sidhik, Siraj; Mohite, Aditya D
    Perovskite solar cells have gained significant attention in recent years due to their potential as a low-cost and highly efficient alternative to traditional silicon-based solar cells. In particular, 3D perovskites have shown exceptional performance in solar cells, but their stability remains a concern. To address this issue, researchers have been exploring the use of 2D perovskites, which offer enhanced stability due to their reduced dimensionality. This thesis aims to investigate the role of 2D perovskites in enhancing the efficiency and stability of 3D perovskite solar cells, as well as exploring the combination of 3D/2D perovskites to further enhance the efficiency and stability of the solar cells. The thesis presents a simple and scalable approach for the fabrication of 2D perovskite thin films with a homogenous layer thickness, termed as the "phase-selective method". This method involves the dissolution of single-crystalline powders with a homogeneous perovskite layer thickness in desired solvents to fabricate thin films. In situ characterizations reveal the presence of sub-micrometer-sized seeds in solution that preserve the memory of the dissolved single crystals and dictate the nucleation and growth of grains with an identical thickness of the perovskite layers in thin films. This approach can lead to the production of high-quality 2D perovskite thin films, which can enhance the stability and efficiency of solar cells. In the second part, the thesis presents a study on the development of highperformance 2D perovskite solar cells using Li-doped nickel oxide (NiOX) as a hole transport layer (HTL). The incorporation of Li-doped NiOX significantly improves the morphology, crystallinity, and orientation of 2D perovskite films and affords a superior band alignment, facilitating efficient charge extraction. Furthermore, 2D PSCs with Li-doped NiOX exhibit excellent photostability without the need for external thermal management, which is a significant advantage for practical applications. Finally, the thesis addresses the challenge of achieving solution-processed heterostructures in halide perovskites by developing a new approach to grow phasepure 2D halide perovskite stacks of the desired composition, thickness, and bandgap onto 3D perovskites without dissolving the underlying substrate. The resulting 3D/2D bilayer exhibited a high photovoltaic efficiency and exceptional stability, indicating that the 3D/2D bilayer inherits the intrinsic durability of 2D perovskite without compromising efficiency. Overall, this thesis presents several significant contributions towards the development of highly efficient and stable perovskite solar cells. The phase-selective method for fabricating 2D perovskite thin films can lead to the production of high quality 2D perovskites, while the use of Li-doped NiOX as an HTL can significantly improve the efficiency and stability of 2D perovskite solar cells. Additionally, the development of a new approach to grow 2D halide perovskite stacks onto 3D perovskites can pave the way for future developments in the field of perovskite solar cells. These findings have significant implications for the development of a clean energy future.
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    Morphology controlled All-Inorganic 2D Perovskite and Transition-Metal Dichalcogenides materials synthesis, characterization and application
    (2023-09-01) Shuai, Xinting; Mohite, Aditya D; Ajayan, Pulickel M
    In recent years, 2D hybrid Ruddlesden-Popper (RP) halide perovskites have garnered significant attention due to their tunable optical and electronic properties alongside impressive stability. Their versatile applications span fields such as light emitting diodes (LEDs), field-effect transistors (FETs), photodetectors, and solar cells. This thesis delves into the evolution of traditional metal halide perovskites and 2D RP perovskites. Notably, emerging within this landscape are the all-inorganic 2D RP Cs2PbI2Cl2 (Pb-based n=1) and Cs2SnI2Cl2 (Sn-based n=1) perovskites, recognized for robust UV-light responsiveness, thermal stability, and remarkable carrier mobility. An innovative achievement is the synthesis of Pb and Sn-based n=1 2D RP perovskite films boasting sub-millimeter single crystal grains via a one-step CVD process at atmospheric pressure. These perovskites showcase a distinctive "tiled" crystal morphology and horizontally-oriented octahedral layers. The study advances to encompass the pioneering fabrication of multilayered Cs3Pb2I3Cl4 (Pb-based n=2) and Cs3Sn2I3Cl4 (Sn-based n=2) films, characterized by X-ray diffraction (XRD) and density functional theory (DFT) calculations for refined crystallographic structures. Complementary DFT calculations and experimental optical spectroscopy discern bandgap energy shifts attributable to quantum confinement effects. Intriguingly, a bias-free photodetector is realized using Sn-based n=1 perovskite, showcasing reproducible photocurrent and a swift 84ms response time. This research underscores the feasibility of growing substantial all-inorganic multilayered 2D perovskite crystals through a singular CVD process, propelling their potential as viable candidates for future photovoltaic applications. Additionally, exploration into using chloride and bromide as halide constituents yields large-area CsPbI2Br films on FTO substrate and CsPbI2Br nanowires on SiO2/Si substrate via the CVD method. Furthermore, the scope broadens to Transition-Metal Dichalcogenides materials, another semiconductor class commonly grown through CVD. Tailoring flow rates facilitates the fabrication of expansive MoS2 and WS2 films via a salt-assisted approach. For gas sensor applications, various chip treatment methodologies including wet-transfer, maskless lithography, and O2 plasma etching are investigated.
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    Optical Studies on Functionalized Graphene Systems
    (2014-05-05) Galande, Charudatta; Ajayan, Pulickel M.; Weisman, R. Bruce; Yakobson, Boris I.; Mohite, Aditya D
    Graphene, the ‘wonder material’, has received a lot of attention for its excellent electronic properties. However, the lack of a band gap severely limits its use, especially in optoelectronic applications. Therefore, opening a band gap in Graphene and controllably modifying its band structure has long been the holy grail in the physics of Graphene. Of these methods, chemical functionalization offers the most degrees of freedom in controllably modifying the band structure of Graphene. Graphene Oxide (GO), the most widely studied chemical derivative of Graphene exhibits a host of optical phenomena such as broadband tunable fluorescence, multiphoton-induced absorption and emission etc. and presents an excellent platform for studying the effects of chemical functionalization on the optical properties of Graphene. In the present work, we first deal with the issue of origin of fluorescence in GO. It is argued that the broadband emission arises due to localized states created on the Graphene surface due to presence of functional groups, and not due to quantum confinement. Next, we attempt to find which of the many functional groups in GO contribute the most to the emission intensity. We find that the carbonyl and epoxide functional groups contribute the most to fluorescence. Further, we find that irradiation with a laser causes an enhancement in the PL of multilayered GO sheets by increasing the density of carbonyl functional groups on the basal plane. This interesting phenomenon is proposed to occur due to a reaction between the oxygen-functionalized basal plane and water molecules trapped between the GO multilayers. We have also developed a method for synthesizing large-area Graphene by chemical vapor deposition (CVD) using liquid precursors. This opens up a host of new possibilities for substitutional doping of Graphene by using liquid precursors containing the dopant atoms.
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    The Design of High Performance Integrated Perovskite-based Devices for Solar Fuels
    (2023-12-12) Fehr, Austin; Mohite, Aditya D; Wong, Michael S
    The critical limitations of solar energy, which are temporal and geographic mismatches with consumption as well as utilization for material manufacturing, can be addressed with solar fuels. However, no direct solar-to-chemical conversion processes have reached commercial scale. Direct, efficient, integrated solar-to-chemical energy conversion via photoelectrochemical cells (PECs) is a promising route to low-cost, scaled solar fuel manufacture. Historical limitations in conversion efficiency and material cost have hindered the deployment of PECs. The recent and rapid advances in halide perovskite solar cells, achieving >26% power conversion efficiency with low material costs and facile processing, have opened new avenues for PECs. In the first chapter, we overcome the key hurdle to perovskite-based PECs through the design of a conductive adhesive-barrier which can simultaneously protect the sensitive optoelectronic components without adding series resistance, achieving 13.4% solar to hydrogen (STH) efficiency with single-junction perovskite solar cells and 20.8% STH with silicon-perovskite tandems. In the second thrust, we conduct a robust technoeconomic analysis to identify further hurdles to commercialization and suggest target metrics and figures of merit for future research to achieve commercially competitive green hydrogen at <$2/kg. In the third and final thrust, we demonstrate a design protocol that reduces the key contributor to panel cost, catalyst material price, by an order of magnitude while preserving or increasing STH and lifetime. This constellation of work will be the bedrock for the commercial proofing of PEC water-splitting, and a platform for other reactions.
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    Understanding structural dynamics using in-situ correlated measurements for halide perovskites
    (2023-11-03) Li, Wenbin; Mohite, Aditya D
    Organic-inorganic hybrid halide perovskites have emerged as a new semiconductor platform for next-generation optoelectronic devices. The standard “3D” perovskite materials, with chemical formula ABX3, where A represents an organic cation, B represents a metal, and X represents a halide, have shown immense promises due to its high power conversion efficiencies (compared to silicon). However, their intrinsic instability under realistic operating conditions limits their implementation in optoelectronic technologies of the future. On the other hand, layered two-dimensional (2D) perovskites, a subclass of hybrid perovskites, have demonstrated stability performances closer to industrial standard but with a lower efficiencies. These materials are composed of large organic molecules which are inserted into their lattice, breaking the 3D perovskite structure into layered slabs of controllable thickness and composition. In this thesis, we will explore the advances in fabricating 2D and 3D halide perovskite materials for high performance optoelectronic applications and understand the structural dynamics of halide perovskites during thin-film formation and external stimuli (realistic operating conditions). This dissertation is split into 4 main parts. First, I will be discussing the background of halide perovskite (both 2D and 3D) through a structure standpoint. Second, I will be reporting a unique approach to synthesize phase pure high n value 2D perovskite single crystals that utilizes machine learning. In addition, I will discuss a novel fabrication process of synthesizing phase pure 2D perovskite thin-films for solar cell application. Third, we will continue the work by discussing the durability of the 2D perovskite devices and the structural and electronic behaviors under light illumination. Lastly, we will tackle the problem of fabricating phase stable "black” alpha-phase FAPbI3 perovskite using 2D perovskite crystals as additives.