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Hole Transport Materials for Solid-State Mesoscopic Solar Cells
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. (Anders Hagfeldt)
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The solid-state mesoscopic solar cells (sMSCs) have been developed as a promising alternative technology to the conventional photovoltaics. However, the device performance suffers from the low hole-mobilities and the incomplete pore filling of the hole transport materials (HTMs) into the mesoporous electrodes. A variety of HTMs and different preparation methods have been studied to overcome these limitations. There are two types of sMSCs included in this doctoral thesis, namely solid-state dye-sensitized solar cells (sDSCs) and organometallic halide perovskite based solar cells.

Two different types of HTMs, namely the small molecule organic HTM spiro-OMeTAD and the conjugated polymer HTM P3HT, were compared in sDSCs. The photo-induced absorption spectroscopy (PIA) spectra and spectroelectrochemical data suggested that the dye-dye hole conduction occurs in the absence of HTM and appears to be of significant importance to the contribution of hole transport.

The PIA measurements and transient absorption spectroscopy (TAS) indicated that the oxidized dye was efficiently regenerated by a small molecule organic HTM TPAA due to its excellent pore filling. The conducting polymer P3HT was employed as a co-HTM to transfer the holes away from TPAA to prohibit the charge carrier recombination and to improve the hole transport.

An alternative small molecule organic HTM, MeO-TPD, was found to outperform spiro-OMeTAD in sDSCs due to its more efficient pore filling and higher hole-mobility. Moreover, an initial light soaking treatment was observed to significantly improve the device performance due to a mechanism of Li+ ion migration towards the TiO2 surface.

In order to overcome the infiltration difficulty of conducting polymer HTMs, a state-of-the-art method to perform in-situ photoelectrochemical polymerization (PEP) in an aqueous micellar solution of bis-EDOT monomer was developed as an environmental-friendly alternative pathway with scale-up potential for constructing efficient sDSCs with polymer HTMs.

Three different types of HTMs, namely DEH, spiro-OMeTAD and P3HT, were used to investigate the influence of HTMs on the charge recombination in CH3NH3PbI3 perovskite based sMSCs. The photovoltage decay measurements indicate that the electron lifetime (τn) of these devices decreases by one order of magnitude in the sequence τspiro-OMeTAD > τP3HT > τDEH.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. , 110 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1181
Keyword [en]
mesoscopic solar cells, solid-state dye-sensitized solar cells, organometallic halide perovskite, hole transport materials, mesoporous TiO2, conjugated polymer, sensitizer, transient absorption spectroscopy, photo-induced absorption spectroscopy, in-situ photoelectrochemical polymerization, spiro-OMeTAD, P3HT, TPAA, MeO-TPD, bis-EDOT, DEH, Li+ ion migration, charge recombination, electron lifetime
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-232271ISBN: 978-91-554-9038-6 (print)OAI: oai:DiVA.org:uu-232271DiVA: diva2:747396
Public defence
2014-10-31, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2014-10-08 Created: 2014-09-16 Last updated: 2015-01-23Bibliographically approved
List of papers
1. Comparing spiro-OMeTAD and P3HT hole conductors in efficient solid state dye-sensitized solar cells
Open this publication in new window or tab >>Comparing spiro-OMeTAD and P3HT hole conductors in efficient solid state dye-sensitized solar cells
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2012 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, no 2, 779-789 p.Article in journal (Refereed) Published
Abstract [en]

Two hole conductor materials, spiro-OMeTAD and P3HT, were compared in solid-state dye-sensitized solar cells. Two organic dyes containing one anchor unit (D35) or two anchor units (M3) were used in the comparison. Absorbed photon to current conversion efficiency close to unity was obtained for the devices with spiro-OMeTAD. Energy conversion efficiencies of 4.7% and 4.9% were measured for the devices with spiro-OMeTAD and the dyes D35 and M3, respectively. For the devices using the P3HT hole conductor the results were rather different comparing the two dye molecules, with energy conversion efficiencies of 3.2% and 0.5% for D35 and M3, respectively. Photo-induced absorption measurements suggest that the regeneration of the dyes, and the polymer infiltration, is not complete using P3HT, while spiro-OMeTAD regenerates the dyes efficiently. However, the TiO(2)/D35/P3HT system shows rather high energy conversion efficiency and electrochemical oxidation of the dyes on TiO(2) indicates that D35 have a more efficient dye to dye hole conduction than M3, which thereby might explain the higher performance. The dye hole conduction may therefore be of significant importance for optimizing the energy conversion in such hybrid TiO(2)/dye/polymer systems.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-169228 (URN)10.1039/c1cp23031j (DOI)000298552800042 ()
Available from: 2012-03-02 Created: 2012-02-24 Last updated: 2017-12-07Bibliographically approved
2. Combining a Small Hole-Conductor Molecule for Efficient Dye Regeneration and a Hole-Conducting Polymer in a Solid-State Dye-Sensitized Solar Cell
Open this publication in new window or tab >>Combining a Small Hole-Conductor Molecule for Efficient Dye Regeneration and a Hole-Conducting Polymer in a Solid-State Dye-Sensitized Solar Cell
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2012 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 34, 18070-18078 p.Article in journal (Refereed) Published
Abstract [en]

In dye-sensitized solar cells (DSC) an efficient transfer of dioles from the oxidized dye to the contact is necessary, which in solid-state DSC is performed by hole-conductor molecules. In this report we use photoinduced absorption and transient absorption spectroscopy to show that a small hole-conducting molecule, tris(p-anisyl)amine, regenerates dye molecules in the pores of the dye-sensitized TiO2 nanoparticle electrode efficiently even for thick (>5 mu m) electrodes. For similar thicknesses we observe incomplete regeneration using a larger polymer hole-conductor. However, the performance of the solar cells with the small hole-conductor molecules is poor due to that inefficient hole conduction in these small molecules may limit the collection of the charges at the contacts. Polymer hole-conductors, which may have a good hole conductivity, also have a high molecular weight, which makes these polymers difficult to infiltrate into the smallest pores in the electrode. We show that a conducting polymer, P3HT, may be added to the small molecule hole-conductor, to enable better transport of the charges to the contact and to reduce recombination and therefore increase the photocurrent. This new device construction with a small molecule efficiently regenerating the dye molecules, and a polymer conducting the holes to the contact is therefore a promising pathway for solid-state dye-sensitized solar cells.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-182776 (URN)10.1021/jp3052449 (DOI)000308120000010 ()
Available from: 2012-10-17 Created: 2012-10-15 Last updated: 2017-12-07Bibliographically approved
3. Initial Light Soaking Treatment Enables Hole Transport Material to Outperform Spiro-OMeTAD in Solid-State Dye-Sensitized Solar Cells
Open this publication in new window or tab >>Initial Light Soaking Treatment Enables Hole Transport Material to Outperform Spiro-OMeTAD in Solid-State Dye-Sensitized Solar Cells
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2013 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 19, 7378-7385 p.Article in journal (Refereed) Published
Abstract [en]

Efficient solid state dye-sensitized solar cells (sDSCs) were obtained using a small hole transport material, MeO-TPD (N,N,N',N'-tetrakis(4-methoxyphenyl)benzidine), after an initial light soaking treatment. It was discovered that the light soaking treatment for the MeO-TPD based solar cells is essential in order to achieve the high efficiency (4.9%), which outperforms spiro-OMeTAD based sDSCs using the same dye and device preparation parameters. A mechanism based on Li+ ion migration is suggested to explain the light soaking effect. It was observed that the electron lifetime for the MeO-TPD based sDSC strongly increases after the light soaking treatment, which explains the higher efficiency. After the initial light soaking treatment the device efficiency remains considerably stable with only 0.2% decrease after around 1 month (unsealed cells stored in dark).

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-202919 (URN)10.1021/ja403344s (DOI)000319250200042 ()
Note

De två (2) första författarna delar förstaförfattarskapet.

Available from: 2013-07-01 Created: 2013-07-01 Last updated: 2017-12-06
4. New Approach for Preparation of Efficient Solid-State Dye-Sensitized Solar Cells by Photoelectrochemical Polymerization in Aqueous Micellar Solution
Open this publication in new window or tab >>New Approach for Preparation of Efficient Solid-State Dye-Sensitized Solar Cells by Photoelectrochemical Polymerization in Aqueous Micellar Solution
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2013 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 23, 4026-4031 p.Article in journal (Refereed) Published
Abstract [en]

Hereby, we present a new, cost-effective, and environmentally friendly method of preparing an efficient solid-state dye-sensitized solar cell (sDSC) using a PEDOT conducting polymer as the hole conductor and a recently developed organic sensitizer. PEDOT is generated and deposited on the dye-sensitized TiO2 electrode by in situ photoelectropolymerization of bis-EDOT in aqueous micellar solution. The advantages of this approach are the use of water as the solvent and the obtainment of a sDSC simply by adding a silver layer on the as-obtained polymer film deposited on dye/TiO2 without the need for electrolytic solution. The sDSC containing the film prepared as above is compared to those where the organic dye is used to generate the same polymer film but in organic solvent. The energy conversion efficiency values of the two cells appear comparable, 4.8% for sDSC prepared in the aqueous-phase polymerized PEDOT and 6% for the sDSC prepared with in organic-phase polymerized PEDOT.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-214018 (URN)10.1021/jz4021266 (DOI)000328101000002 ()
Available from: 2014-01-08 Created: 2014-01-07 Last updated: 2017-12-06Bibliographically approved
5. Effect of Different Hole Transport Materials on Recombination in CH3NH3PbI3 Perovskite-Sensitized Mesoscopic Solar Cells
Open this publication in new window or tab >>Effect of Different Hole Transport Materials on Recombination in CH3NH3PbI3 Perovskite-Sensitized Mesoscopic Solar Cells
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2013 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 9, 1532-1536 p.Article in journal (Refereed) Published
Abstract [en]

We report on perovskite (CH3NH3)PbI3-sensitized solid-state solar cells using spiro-OMeTAD, poly(3-hexylthiophene-2,5-diyl) (P3HT) and 4-(diethylamino)benzaldehyde diphenylhydrazone (DEH) as hole transport materials (HTMs) with a light to electricity power conversion efficiency of 8.5%, 4.5%, and 1.6%, respectively, under AM 1.5G illumination of 1000 W/m(2) intensity. Photoinduced absorption spectroscopy (PIA) shows that hole transfer occurs from the (CH3NH3)PbI3 to HTMs after excitation of (CH3NH3)PbI3. The electron lifetime (tau(e)) in these devices are in the order Spiro-OMeTAD > P3HT > DEH, while the charge transport time (t(tr)) is rather similar. The difference in tau(e) can therefore explain the lower efficiency of the devices based on P3HT and DEH. This report shows that the nature of the HTM is essential for charge recombination and elucidates that finding an optimal HTM for the perovskite solar cell includes controlling the perovskite/HTM interaction. Design routes for new HTMs are suggested.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-201790 (URN)10.1021/jz400638x (DOI)000318536500026 ()
Available from: 2013-06-17 Created: 2013-06-17 Last updated: 2017-12-06Bibliographically approved

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