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    Photophysical Processes in Lead Halide Perovskite Solar Cells Revealed by Ultrafast Spectroscopy

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    Name:
    Esma Ugur - Dissertation - Final Draft.pdf
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    8.518Mb
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    Description:
    Esma Ugur - Dissertation - Final Draft
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    Type
    Dissertation
    Authors
    Ugur, Esma cc
    Advisors
    Laquai, Frédéric cc
    Committee members
    De Wolf, Stefaan cc
    Ooi, Boon S. cc
    Albrecht, Steve
    Program
    Material Science and Engineering
    KAUST Department
    Physical Science and Engineering (PSE) Division
    Date
    2020-09-16
    Permanent link to this record
    http://hdl.handle.net/10754/665564
    
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    Abstract
    Metal halide perovskites have emerged as photoactive materials in solution-processed devices thanks to their unique properties such as high absorption coefficient, sharp absorption edge, long carrier diffusion lengths, and tunable bandgap, together with ease of fabrication. The single-junction perovskite solar cells have reached power conversion efficiencies of more than 25%. Although the efficiency of perovskite devices has increased tremendously in a very short time, the efficiency is still limited by carrier recombination at defects and interfaces. Thus, understanding these losses and how to reduce them is the way forward towards the Shockley-Queisser limit. This thesis aims to apply ultrafast optical spectroscopy techniques to investigate the recombination pathways in halide perovskites, and understand the charge extraction from perovskite to transport layers and nonradiative losses at the interface. The first part focuses on perovskite solar cells with planar n–i–p device architecture which offers significant advantages in terms of large scale processing, the potential use of flexible substrates, and applicability to tandems. In addition to the optimization of MAPbI3 solar cell fabrication using a modified sequential interdiffusion protocol, the photophysics of perovskites exposed to humid air and illumination are discussed. The MAPbI3 film processed with the addition of glycol ethers to the methylammonium iodide solution results in the control of PbI2 to perovskite conversion dynamics, thus enhanced morphology and crystallinity. For samples exposed to humid air and illumination, the formation of sub-bandgap states and increased trap-assisted recombination are observed, using highly-sensitive absorption and time-resolved photoluminescence measurements, respectively. It appears that such exposure primarily affects the perovskite surface. The second part discusses the hole extraction from Cs0.07Rb0.03FA0.765MA0.135PbI2.55Br0.45 to the polymeric hole transport layer and interfacial recombination using ultrafast transient absorption spectroscopy technique. To illustrate this, PDPP-3T was used as HTL, since its ground state absorption is red-shifted compared to the perovskite’s photobleach, thereby allowing direct probing of the interfacial hole extraction and recombination. Moreover, carrier diffusion is investigated by varying the perovskite film thickness, and carrier mobility is found to be 39 cm2V-1s-1. Finally, hole extraction is found to be one order of magnitude faster than the recombination at the interface.
    Citation
    Ugur, E. (2020). Photophysical Processes in Lead Halide Perovskite Solar Cells Revealed by Ultrafast Spectroscopy. KAUST Research Repository. https://doi.org/10.25781/KAUST-6628H
    DOI
    10.25781/KAUST-6628H
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-6628H
    Scopus Count
    Collections
    Dissertations; Physical Science and Engineering (PSE) Division; Material Science and Engineering Program

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