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Mechanistic Insights into Solid-State p-Type Dye-Sensitized Solar Cells
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Stockholm Univ, Dept Mat & Environm Chem, S-10691 Stockholm, Sweden.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.ORCID iD: 0000-0002-3442-3672
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2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 43, p. 26151-26160Article in journal (Refereed) Published
Abstract [en]

The study of p-type dye sensitized solar cells (p-DSCs) is appealing but challenging. Although the devices have been studied for 20 years, the light conversion efficiency lags far behind those of n-DSCs. Very recently, on the basis of a core-shell structure, a novel solid-state p-DSC (p-ssDSCs) has been fabricated, which showed great enhancement in open-circuit voltage and dye regeneration rate. To further improve the performance of such devices, charge diffusion, recombination process, and the main limiting factors have to be understood. In the present paper, core-shell p-ssDSCs with ZnO as an electron conductor were fabricated by atomic layer deposition. The charge transport time was determined to be ca. 0.1 ms, which is about 2 orders of magnitude faster than those of typical liquid devices with I-/I-3(-) as a redox mediator. As a consequence, the devices exhibit the highest reported charge diffusion coefficient (D-d)' among p-DSCs. It is ascribed to an electron-limiting diffusion process by the ambipolar diffusion model, suggesting a different charge-transport-determining mechanism in contrast to liquid p-DSCs. The charge recombination rate is 1-2 orders of magnitude slower than its charge transport time, mandating that the estimated charge collection efficiency is near unity. Detailed analysis of the incident photon-to-electron conversion efficiency suggests that the energy conversion efficiency in these p-ssDSCs is currently limited by a large fraction of dyes that is not fully electrically connected in the device.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC , 2019. Vol. 123, no 43, p. 26151-26160
National Category
Physical Chemistry Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-397591DOI: 10.1021/acs.jpcc.9b08251ISI: 000493865700013OAI: oai:DiVA.org:uu-397591DiVA, id: diva2:1372606
Available from: 2019-11-25 Created: 2019-11-25 Last updated: 2020-01-15Bibliographically approved
In thesis
1. Exploring Dye-Sensitized Mesoporous NiO Photocathodes: from Mechanism to Applications
Open this publication in new window or tab >>Exploring Dye-Sensitized Mesoporous NiO Photocathodes: from Mechanism to Applications
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Increasing attention has been paid on solar energy conversion since the abundant solar energy possesses the potential to solve the problems on energy crisis and climate change. Dye-sensitized mesoporous NiO film was developed as one of the attractive photocathodes to fabricate p-type dye-sensitized solar cells (p-DSCs) and dye-sensitized photoelectrosynthetic cells (p-DSPECs) for electricity and chemical fuels generation, respectively. In this thesis, we designed a well-structured NiO-dye-TiO2 configuration by an atomic layer deposition (ALD) technique, with an organic dye PB6 as the photosensitizer. From kinetic studies of charge separation, ultrafast hole injection (< 200 fs) was observed from the excited state of PB6 dye into the valence band of NiO; dye regeneration (electron injection) was in t1/2 ≤ 500 fs, which is the fastest reported in any DSCs. On the basis of NiO-dye-TiO2 configuration, we successfully fabricated solid-state p-type DSCs (p-ssDSCs). Insertion of an Al2O3 layer was adopted to reduce charge recombination, i.e. NiO-dye-Al2O3-TiO2. Theoretically, such a configuration is possible to maintain efficient charge separation and depressed charge recombination. Based on NiO-dye-Al2O3-TiO2 configuration, the open-circuit voltage was improved to 0.48 V. Replacing electron conductor TiO2 with ZnO, short-circuit current density was increased to 680 μA·cm-2. The photocatalytic current density for H2 evolution was improve to 100 μA·cm-2 with a near unity of Faraday efficiency in p-DSPECs.

However, to further improve the performance of p-DSCs is very challenging. In p-ssDSCs, the limitation was confirmed from the poor electronically connection of the electron conductor (TiO2 or ZnO) inside the NiO-dye films. We further investigated the electronic property of surface states on mesoporous NiO film. We found that the surface sates, not the bulk, on NiO determined the conductivity of the mesoporous NiO films. The dye regeneration in liquid p-DSCs with I-/I3- as redox couples was significantly affected by surface states. A more complete mechanism is suggested to understand a particular hole transport behavior reported in p-DSCs, where hole transport time is independent on light intensity. The independence of charge transport is ascribed to the percolation effect in the hole hopping on the surface states.

 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2020. p. 73
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1896
Keywords
NiO, p-type, dye-sensitized solar cells, solid state, charge separation, charge recombination, charge diffusion, transport time, surface states, electron conductor, dye regeneration
National Category
Physical Chemistry
Research subject
Chemistry with specialization in Chemical Physics
Identifiers
urn:nbn:se:uu:diva-402415 (URN)978-91-513-0852-4 (ISBN)
Public defence
2020-03-03, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
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Available from: 2020-02-11 Created: 2020-01-15 Last updated: 2020-02-14

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Tian, LeiTörndahl, TobiasPati, Palas BaranZhang, Zhi-BinKubart, TomasHao, YanBoschloo, GerritTian, Haining

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