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Molecular-structure control of electron transferdynamics of push–pull porphyrins as sensitizers forNiO based dye sensitized solar cells
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström. (Prof Hammarstrom Leif's group)
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2016 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, 77184-77194 p.Article in journal (Refereed) Published
Abstract [en]

Porphyrin dyes were synthesized for use in p-type (NiO) dye sensitized solar cells based on different designprinciples. One porphyrin was designed with a significant charge transfer character in the excited statebecause of push–pull effects of the substituents. Another porphyrin had instead an appended NDIacceptor group (NDI ¼ naphthalene diimide). The dyes were characterized by spectroscopic,electrochemical and DFT methods. Solar cells based on sensitized, meso-porous NiO showed ratherpoor performance compared to other organic dyes, but with a clear improvement for the dye with theNDI acceptor. Ultrafast transient absorption spectroscopy and nanosecond laser photolysis showed thathole injection into NiO was followed by unusually rapid charge recombination, predominantly ona 50–100 ps time scale, which is likely the main reason for the poor photovoltaic performance. Againthe porphyrin with the NDI group showed a more long-lived charge separation that should lead to betterdye regeneration in a solar cell, which can explain its better photovoltaic performance.

Place, publisher, year, edition, pages
RSC, 2016. Vol. 6, 77184-77194 p.
Keyword [en]
porphyrins, electron transfer dynamics, NiO
National Category
Physical Chemistry
Research subject
Chemistry with specialization in Chemical Physics
Identifiers
URN: urn:nbn:se:uu:diva-301387DOI: 10.1039/c6ra15195gOAI: oai:DiVA.org:uu-301387DiVA: diva2:954399
Available from: 2016-08-22 Created: 2016-08-22 Last updated: 2016-08-31Bibliographically approved
In thesis
1. Exploring Electron Transfer Dynamics of Novel Dye Sensitized Photocathodes: Towards Solar Cells and Solar Fuels
Open this publication in new window or tab >>Exploring Electron Transfer Dynamics of Novel Dye Sensitized Photocathodes: Towards Solar Cells and Solar Fuels
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The design of dyes for NiO-based dye-sensitized solar cells (DSSCs) has drawn attention owing to their potential applications in photocatalysis and because they are indispensable for the development of tandem dye-sensitized solar cells. The understanding of the electron transfer mechanisms and dynamics is beneficial to guide further dye design and further improve the performance of photocathode in solar cells and solar fuel devices.

Time-resolved spectroscopy techniques, especially femtosecond and nanosecond transient absorption spectroscopy, supply sufficient resolution to get insights into the charge transfer processes in p-type dye sensitized solar cell and solar fuel devices. In paper I-V, several kinds of novel organic “push-pull” and inorganic charge transfer dyes for sensitization of p-type NiO, were systematically investigated by time-resolved spectroscopy, and photo-induced charge transfer dynamics of the organic/inorganic dyes were summarized. The excited state and reduced state intermediates were investigated in solution phase as references to confirm the charge injection and recombination on the NiO surface. The charge recombination kinetics is remarkably heterogeneous in some cases occurring on time scales spanning at least six orders of magnitude even for the same dye.

In this thesis, we also proposed a novel concept of solid state p-type dye sensitized solar cells (p-ssDSSCs) for the first time (paper VI), using an organic dye P1 as sensitizer on mesoporous NiO and phenyl-C61-butyric acid methyl ester (PCBM) as electron conductor. Femtosecond and nanosecond transient absorption spectroscopy gave evidence for sub-ps hole injection from excited P1 to NiO, followed by electron transfer from P1●- to PCBM. The p-ssDSSCs device showed an impressive 620 mV open circuit photovoltage.

Chapter 6 (paper VII) covers the study of electron transfer mechanisms in a covalently linked dye-catalyst (PB-2) sensitized NiO photocathode, towards hydrogen producing solar fuel devices. Hole injection from excited dye (PB-2*) into NiO VB takes place on dual time scales, and the reduced PB-2 (PB-2●-) formed then donates an electron to the catalyst unit.  The subsequent regeneration efficiency of PB-2 by the catalyst unit (the efficiency of catalyst reduction) is determined to ca. 70%.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 80 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1418
Keyword
Electron transfer, Laser spectroscopy, Femtosecond spectroscopy, Transient absorption, NiO, DSSCs, DSSFDs, Charge separation, Solar energy conversion, Nanosecond photolysis, Photophysics
National Category
Chemical Sciences
Research subject
Chemistry with specialization in Chemical Physics
Identifiers
urn:nbn:se:uu:diva-302263 (URN)978-91-554-9678-4 (ISBN)
Public defence
2016-10-21, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2016-09-27 Created: 2016-08-31 Last updated: 2016-09-27

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Available from 2017-08-08 00:00

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