Energy transfer processes in organic and inorganic materials for photovoltaic devices

Menelaou, C

Abstract:: This thesis is concerned with energy transport processes in a series of low-bandgap copolymers, solution processable hybrid organic-inorganic perovskite materials, and donor-acceptor triad dyes which are used in photovoltaic cells and solar concentrator devices. These processes are investigated using time-resolved photoluminescence (PL) spectroscopy techniques which allow the investigation of transport processes with sub-ps time resolution.

Two donor-acceptor-donor triad dyes compos...
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APA Style

Menelaou, C. (2015). Energy transfer processes in organic and inorganic materials for photovoltaic devices [PhD thesis]. University of Oxford.

MLA Style

Menelaou, C. Energy Transfer Processes in Organic and Inorganic Materials for Photovoltaic Devices. 2015. University of Oxford, PhD thesis.

Chicago Style

Menelaou, C. 2015. “Energy Transfer Processes in Organic and Inorganic Materials for Photovoltaic Devices.” PhD thesis, University of Oxford.
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Authors

+ Menelaou, C More by this author

Department:: Physics
Department:: University of Oxford
Role:: Author

Contributors

+ Herz, L

Department:: University of Oxford
Role:: Supervisor

+ Merck Chemicals Ltd More from this funder

+ Engineering and Physical Sciences Research Council More from this funder

DOI:: 10.5287/ora-jn0jn6jk1
Type of award:: DPhil
Level of award:: Doctoral
Awarding institution:: University of Oxford

Keywords:: Exciton diffusion length

Organic Photovoltaics

Ultrafast spectroscopy

Energy Transfer

Luminescent Solar Concentrator

Bulk heterojunctions

Photoluminescence upconversion

Perovskite solar cells

Photoluminescence spectroscopy
Subjects:: Organic Semiconductors

Organic Photovoltaics

Condensed Matter Physics

Laser Spectroscopy
UUID:: uuid:6b34de06-6671-4ed0-9adf-99f2ac254f2c
Deposit date:: 2016-03-14
ARK identifier:: ark:/29072/ora_6b34de0666714ed09adf99f2ac254f2c

Related item:: Rapid Energy Transfer Enabling Control of Emission Polarization in Perylene Bisimide Donor-Acceptor Triads
Description:: Materials showing rapid intramolecular energy transfer and polarization switching are of interest for both their fundamental photophysics and potential for use in real-world applications. Here, we report two donor-acceptor-donor triad dyes based on perylene-bisimide subunits, with the long axis of the donors arranged either parallel or perpendicular to that of the central acceptor. We observe rapid energy transfer (less than 2 ps) and effective polarization control in both dye molecules in solution. A distributed-dipole Forster model predicts the excitation energy transfer rate for the linearly arranged triad but severely underestimates it for the orthogonal case. We show that the rapid energy transfer arises from a combination of through-bond coupling and through-space transfer between donor and acceptor units. As they allow energy cascading to an excited state with controllable polarization, these triad dyes show high potential for use in luminescent solar concentrator devices.
Related item:: Effect of Nanocrystalline Domains in Photovoltaic Devices with Benzodithiophene-Based Donor–Acceptor Copolymers
Description:: We have investigated the effects of thin-film morphology on the photovolatic performance for a series of donor-acceptor copolymers based on benzodithiophene donor and benzothiadiazole acceptor units. Photovoltaic devices incorporating polymer:fullerene blends show highest efficiencies (up to 6%) for those polymers exhibiting the least degree of crystallinity in X-ray diffraction patterns and a corresponding lowest surface roughness in thin films. We find that the existence of such crystalline domains in thin polymer films correlates well with spectral signatures of polymer chain aggregates already present in solution prior to casting of the film. Polymer solubility and casting conditions therefore appear to be crucial factors for enhancing efficiencies of photovoltaic devices based on such donor-acceptor copolymers. To examine why the presence of crystallite domains lowers device efficiencies, we measured exciton diffusion lengths by modeling the time-dependent photoluminescence from thin polymer films deposited on an exciton quencher layer of TiO2. We find that exciton diffusion lengths in these materials are substantial (4-7.5 nm) and show some variation with polymer crystallinity. However, ultrafast (1 ps) quenching of the polymer emission from polymer:PCBM blends indicates that the vast majority of excitons rapidly reach the charge-dissociating interface, and hence exciton diffusion does not represent a limiting factor. We therefore conclude that the subsequent charge extraction and lifetimes must be adversely affected by the presence of crystalline domains. We suggest that the formed crystallites are too small to offer significant enhancements in long-range charge carrier mobility but instead introduce domain boundaries which impede charge extraction. For this class of materials, polymer designs are therefore required that target high solubility and chain entropy, leading to amorphous film formation.
Related item:: Electron-Hole Diffusion Lengths Exceeding 1 Micrometer in an Organometal Trihalide Perovskite Absorber
Description:: Organic-inorganic perovskites have shown promise as high-performance absorbers in solar cells, first as a coating on a mesoporous metal oxide scaffold and more recently as a solid layer in planar heterojunction architectures. Here, we report transient absorption and photoluminescence-quenching measurements to determine the electron-hole diffusion lengths, diffusion constants, and lifetimes in mixed halide (CH3NH3PbI3-xClx) and triiodide (CH3NH3PbI3) perovskite absorbers. We found that the diffusion lengths are greater than 1 micrometer in the mixed halide perovskite, which is an order of magnitude greater than the absorption depth. In contrast, the triiodide absorber has electron-hole diffusion lengths of ~100 nanometers. These results justify the high efficiency of planar heterojunction perovskite solar cells and identify a critical parameter to optimize for future perovskite absorber development.

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Copyright holder:: Menelaou, C

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Energy transfer processes in organic and inorganic materials for photovoltaic devices

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Energy transfer processes in organic and inorganic materials for photovoltaic devices

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