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XDSC: Excitonic Dye Solar Cells
Uppsala University, Disciplinary Domain of Science and Technology. (Hagfeldt)
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Solar energy is the foremost power source of our planet. Driving photosynthesis on our planet for 3 billion years the energy stored in the form of fossil fuels also originates from the sun. Consumption of fossil fuels to generate energy is accompanied with CO2 emission which affects the earth's climate in a serious manner.

Therefore, alternative ways of converting energy have to be found. Solar cells convert sunlight directly into electricity and are therefore an important technology for future electricity generation.

In this work solar cells based on the inorganic semiconductor titanium dioxide and hole-transporting dyes are investigated. These type of solar cells are categorized as hybrid solar cells and are conceptually related to both dye-sensitized solar cells and organic solar cells. Light absorption in the bulk of the hole-transporting dye layer leads to the formation of excitons that can be harvested at the organic/inorganic interface. Two design approaches were investigated: 1) utilizing a multilayer of a hole-transporting dye and 2) utilizing a hole-transporting dye as light harvesting antenna to another dye which is bound to the titanium dioxide surface. 

Using a multiple dye layer in titanium dioxide/hole transporting dye devices, leads to an improved device performance as light harvested in the consecutive dye layers can contribute to the photocurrent. In devices using both an inteface-bound dye and a hole-transporting dye, excitation energy can be transferred from the hole-transporting dye to the interface dye. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. , 93 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 899
Keyword [en]
hybrid solar cells, energy transfer, dye-sensitized solar cells, TiO2, small-molecular semiconductor, hole-transporting dye
National Category
Physical Chemistry
Research subject
Chemistry with specialization in Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-168608ISBN: 978-91-554-8279-4 (print)OAI: oai:DiVA.org:uu-168608DiVA: diva2:500212
Public defence
2012-03-30, Polhemsalen, Ångström laboratoriet, Lägerhyddsvägen 1, Uppsala, 09:55 (English)
Opponent
Supervisors
Available from: 2012-03-09 Created: 2012-02-13 Last updated: 2012-03-29Bibliographically approved
List of papers
1.
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2. Contribution from a hole-conducting dye to the photocurrent in solid-state dye-sensitized solar cells
Open this publication in new window or tab >>Contribution from a hole-conducting dye to the photocurrent in solid-state dye-sensitized solar cells
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2011 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 45, 20172-20177 p.Article in journal (Refereed) Published
Abstract [en]

The hole transporting medium in solid-state dye-sensitized solar cells can be utilized to harvest sunlight. Herein we demonstrate that a triphenylamine-based dye, used as hole-transporting medium, contributes to the photocurrent in a squaraine-sensitized solid-state dye-sensitized solar cell. Steady-state photoluminescence measurements have been used to distinguish between electron transfer and energy transfer processes leading to energy conversion upon light absorption in the hole-transporting dye.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-163256 (URN)10.1039/c1cp22493j (DOI)000296871500019 ()
Available from: 2011-12-13 Created: 2011-12-09 Last updated: 2017-12-08Bibliographically approved
3. Spray-pyrolyzed vs spin-cast titania films in bilayer hybrid solar cells with a small-molecular hole transporting dye
Open this publication in new window or tab >>Spray-pyrolyzed vs spin-cast titania films in bilayer hybrid solar cells with a small-molecular hole transporting dye
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Titania films as acceptor layer in bilayer hybrid solar cell devices were prepared by spray-pyrolysis and by spin-casting. Both preparation methods resulted in anatase titania films with similar optical and electronic properties. Spray pyrolysis resulted in dense TiO2 films grown onto the conducting glass substrates while spin-casting gave rise to titania films with a nanoporous morphology. Hybrid solar cell devices with varying layer thickness of the small molecular semiconducting dye TDCV-TPA were investigated. Devices built with spray-pyrolyzed titania substrates yielded conversion effiencies up to 0.47 %, limited by the exciton diffusion length in TDCV-TPA. Spin-cast titania substrates exhibited short circuits for devices with thin dye layer thickness but gave up to 0.6 % conversion efficiency for thicker dye layers due to the higher interfacial area for charge separation and the dye acting as an insultator.

Keyword
spray-pyrolysis, spin-casting, TiO2, hybrid solar cell
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-168480 (URN)
Available from: 2012-02-12 Created: 2012-02-12 Last updated: 2012-09-18
4. Excitation energy dependent charge separation at small-molecular semiconductor/TiO2 interface
Open this publication in new window or tab >>Excitation energy dependent charge separation at small-molecular semiconductor/TiO2 interface
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Interfacial charge separation in hybrid solar cells depends on the energetic alignment and electronic coupling between the inorganic and organic semiconducting materials at the hetero-interface. In the present work, bilayer solar cells comprising the small molecular semiconducting dye TDCV-TPA (tris-(thienylene-vinylene)-triphenylamine) and dense titanium dioxide (TiO2) films were investigated. The internal quantum efficiency and degree of photoluminescence quenching were found to be excitation energy dependent. The molecular interaction and interfacial energy level alignment was investigated by a combination of UV-Vis and photoelectron spectroscopy. Stationary and time-dependent density functional theory calculations were used to assign and distinguish between experimentally determined molecular energy levels and electronic transitions. Photoelectron spectroscopy results suggest surface induced interactions of TDCV-TPA involving peripheral CN-groups. This may imply a favourable electronic coupling to the inorganic semiconductor for interfacial charge transfer. In an energy level diagram distinguishing between the different electronic transitions in the molecule the differences in the thermodynamic driving force for electron injection were found small. Therefore it is suggested that the observed higher internal quantum efficiency at shorter wavelength can be rationalized by a more favourable driving force for the regeneration of holes created at the hetero-interface at higher excitation energy.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-168483 (URN)
Available from: 2012-02-12 Created: 2012-02-12 Last updated: 2012-09-18
5. Hole transporting dye as light harvesting antenna in dye sensitized TiO2 hybrid solar cells
Open this publication in new window or tab >>Hole transporting dye as light harvesting antenna in dye sensitized TiO2 hybrid solar cells
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The pore volume in solid state dye-sensitized solar cells can be utilized for light harvesting by using hole transporting dyes (HTD) in addition to interface dyes (ID) bound to the surface of the meso-porous metal oxide scaffold. Triphenyl-amine based compounds were used both as HTD (TPTPA) and ID (D5L0A3). Energy transfer from the HTD to ID was investigated using steady state photoluminescence. The photoluminescence of the HTD is quenched in presence of the ID – both for samples where the HTD and ID were dispersed in a solid PMMA matrix and for solid samples measured on ZrO2 films. The regeneration of oxidized ID by the HTD after photo-induced electron injection into TiO2 was investigated using nanosecond transient absorption spectroscopy. In presence of the HTD signals, attributed to oxidized ID, vanished while spectral signatures suggesting the creation of oxidized HTD appeared. In solar cell devices comprising both the ID and HTD the spectral response of the external quantum efficiency shows that both dyes contribute to the photocurrent resulting in a 2-fold increase in photocurrent. The interface dye seems to prevent recombination giving rise to a higher open circuit voltage in the solar cell devices. Due to the increase both in photocurrent and voltage the solar cell device performance increased by a factor of 3. Utilizing a hole-transporting dye in addition to an interfacial sensitizer is a promising design concept for solid state dye sensitized solar cell devices. 

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-168484 (URN)
Available from: 2012-02-12 Created: 2012-02-12 Last updated: 2012-03-29

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