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Organic Hole Transport Materials for Solid-State Dye-Sensitized and Perovskite Solar Cells
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Solid-state dye-sensitized solar cells (ssDSSCs) and recently developed perovskite solar cells (PSCs) have attracted a great attention in the scientific field of photovoltaics due to their low cost, absence of solvent, simple fabrication and promising power conversion efficiency (PCE). In these types of solar cell, the dye molecule or the perovskite can harvest the light on the basis of electron excitation. Afterwards, the electron and hole are collected at the charge transport materials.

Photoelectrochemical polymerization (PEP) is employed in this thesis to synthesize conducting polymer hole transport materials (HTMs) for ssDSSCs. We have for the first time developed aqueous PEP in comparison with the conventional organic PEP with acetonitrile as solvent. This water-based PEP could potentially provide a low-cost, environmental-friendly method for efficient deposition of polymer HTM for ssDSSCs. In addition, new and simple precursors have been tested with PEP method. The effects of dye molecules on the PEP were also systematically studied, and we found that (a) the bulky structure of dye is of key importance for blocking the interfacial charge recombination; and (b) the matching of the energy levels between the dye and the precursor plays a key role in determining the kinetics of the PEP process.

In PSCs, the HTM layer is crucial for efficient charge collection and its long term stability. We have studied different series of new molecular HTMs in order to understand fundamentally the influence of alkyl chains, molecular energy levels, and molecular geometry of the HTM on the photovoltaic performance. We have identified several important factors of the HTMs for efficient PSCs, including high uniformity of the HTM capping layer, perovskite-HTM energy level matching, good HTM solubility, and high conductivity. These factors affect interfacial hole injection, hole transport, and charge recombination in PSCs. By systematical optimization, a promising PCE of 19.8% has been achieved by employing a new HTM H11. We believe that this work could provide important guidance for the future development of new and efficient HTMs for PSCs.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 83 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1408
Keyword [en]
photoelectrochemical polymerization, PEDOT, dye, hole transport material, small molecule, perovskite solar cell
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-300802ISBN: 978-91-554-9659-3OAI: oai:DiVA.org:uu-300802DiVA: diva2:952974
Public defence
2016-10-07, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2016-09-15 Created: 2016-08-14 Last updated: 2016-09-22
List of papers
1. Poly(3,4-ethylenedioxythiophene) Hole-Transporting Material Generated by Photoelectrochemical Polymerization in Aqueous and Organic Medium for All-Solid-State Dye-Sensitized Solar Cells
Open this publication in new window or tab >>Poly(3,4-ethylenedioxythiophene) Hole-Transporting Material Generated by Photoelectrochemical Polymerization in Aqueous and Organic Medium for All-Solid-State Dye-Sensitized Solar Cells
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2014 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 30, 16591-16601 p.Article in journal (Refereed) Published
Abstract [en]

We applied organic donor-pi-acceptor (D-pi-A) sensitizers for photoelectrochemical polymerization (PEP) because of their appropriate energy levels and high light absorption. The polymerized conducting polymer PEDOT was used as hole conductor in all-solid-state dye-sensitized solar cells (ssDSCs). By combination of the D-pi-A sensitizers and the generated PEDOT from PEP of bis-EDOT in acetonitrile, the resulting device showed an average power conversion efficiency of 5.6%. Furthermore, the PEP in aqueous micellar electrolytic medium was also employed because of the ability to decrease oxidation potential of the precursor, thereby making the polymerization process easier. The latter method is a cost-effective and environmentally friendly approach. Using as hole conductor the so-obtained PEDOT from PEP of bis-EDOT in aqueous electrolyte, the devices exhibited impressive power conversion efficiency of 5.2%. To compare the properties of the generated polymer from bis-EDOT in these two PEP methods, electron lifetime, photoinduced absorption (PIA) spectra, and UV-vis-NIR spectra were measured. The results showed that PEDOT from organic PEP exhibits a delocalized conformation with high conductivity and a smooth and compact morphology; a rough morphology with high porosity and polymer structure of relatively shorter chains was assumed to be obtained from aqueous PEP. Therefore, better dye regeneration but faster charge recombination was observed in the device based on PEDOT from aqueous PEP of bis-EDOT. Subsequently, to extend the aqueous PEP approach in consideration of the ability to decrease the oxidation potential of the precursor, the easily available precursor EDOT was for the first time used for PEP in aqueous medium in a variant of the aforementioned procedure, and the device based on the so-obtained PEDOT shows a more than 70-fold increase in efficiency, 3.0%, over that based on the polymer generated from EDOT by PEP in organic media. It was demonstrated that aqueous micellar PEP with EDOT as monomer is an efficient strategy for generation of conducting polymer hole-transporting materials.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-231291 (URN)10.1021/jp412504s (DOI)000339930900037 ()
Available from: 2014-09-08 Created: 2014-09-07 Last updated: 2016-08-25Bibliographically approved
2. Photoelectrochemical Polymerization of EDOT for Solid State Dye Sensitized Solar Cells: Role of Dye and Solvent
Open this publication in new window or tab >>Photoelectrochemical Polymerization of EDOT for Solid State Dye Sensitized Solar Cells: Role of Dye and Solvent
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2015 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 179, 220-227 p.Article in journal (Refereed) Published
Abstract [en]

The aromatic-unit, commercially available, and cost-effective precursor 3, 4-ethylenedioxythiophene (EDOT), was employed instead of bis-EDOT to generate by in-situ photoelectrochemical polymerization (PEP) a conducting polymer-type hole conductor poly (3, 4-ethylenedioxythiophene) (PEDOT) for dye sensitized solar cell (DSC) devices. In order to conduct efficiently the PEP of EDOT, two electrolytic media, aqueous micellar and organic, and two Donor-pi-Acceptor sensitizers, were investigated. By using the electrolytic aqueous micellar medium, the PEP was efficient due to the low oxidation potential of the precursor in water. A DSC device based on PEDOT generated from aqueous PEP showed an energy conversion efficiency (eta) of 3.0% under 100 mWcm (2), higher by two orders of magnitude than that of a DSC device based on PEDOT from organic PEP (eta = 0.04%). The comparison of the properties of the as-obtained PEDOT polymers from aqueous and organic PEP by UV-VIS-NIR measurements shows the formation of PEDOT at a highly doped state from aqueous PEP. The thermodynamic and kinetic requirements for efficiency of PEP process in each medium are investigated and discussed on the basis of the light absorption abilities and electrochemical redox potentials measured for the two organic sensitizers.

Keyword
aqueous micellar electrolyte, conducting polymer, EDOT, hole conductor, solid state dye sensitized solar cell
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-265671 (URN)10.1016/j.electacta.2015.01.077 (DOI)000362292200029 ()
Funder
Swedish Energy AgencyStandUpSwedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2015-11-05 Created: 2015-11-02 Last updated: 2016-08-25Bibliographically approved
3. Solid-State Dye-Sensitized Solar Cells Based on Poly( 3,4ethylenedioxypyrrole) and Metal-Free Organic Dyes
Open this publication in new window or tab >>Solid-State Dye-Sensitized Solar Cells Based on Poly( 3,4ethylenedioxypyrrole) and Metal-Free Organic Dyes
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2014 (English)In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 15, no 6, 1043-1047 p.Article in journal (Refereed) Published
Abstract [en]

Poly(3,4-ethylenedioxypyrrole) (PEDOP), combined with metal-free organic sensitizers, is efficiently used for the first time as the hole-transporting material in solid-state dye-sensitized solar cells. Devices employing PEDOP as the hole conductor and D35 or D21 L6 as the sensitizer show a ten-times-higher energy-conversion efficiency (of 4.5% and 3.3%, respectively) compared to Ru-Z907-based devices. This is due to the efficient suppression of electron recombination.

Keyword
dye-sensitized solar cells, electrochemistry, hole-transporting materials, organic sensitizers, photoelectrochemical polymerization
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-225021 (URN)10.1002/cphc.201301075 (DOI)000334080700008 ()
Available from: 2014-05-26 Created: 2014-05-26 Last updated: 2016-08-25Bibliographically approved
4. Efficient solid-state dye sensitized solar cells: The influence of dye molecular structures for the in-situ photoelectrochemically polymerized PEDOT as hole transporting material
Open this publication in new window or tab >>Efficient solid-state dye sensitized solar cells: The influence of dye molecular structures for the in-situ photoelectrochemically polymerized PEDOT as hole transporting material
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2016 (English)In: NANO ENERGY, ISSN 2211-2855, Vol. 19, 455-470 p.Article in journal (Refereed) Published
Abstract [en]

Solid-state dye sensitized solar cells (sDSCs) with organic small molecule hole transporting materials (HTMs) have limited efficiencies due to the incomplete pore filling of the HTMs in the thick mesoporous electrodes and the low hole conductivity of HTMs. Hereby, highly efficient sDSCs with power conversion efficiency of 7.11% and record photocurrent of 13.4 mA cm-2 are reported, prepared by effectively incorporating in-situ photoelectrochemically polymerized PEDOT as HTM in combination with a multifunctional organic, metal-free dye. In order to fundamentally understand how the dye molecules affect the photoelectrochemical polymerization (PEP), the properties of the generated PEDOT and the photovoltaic performance, sDSCs based on a series of dyes are systematically investigated. Detailed comparative studies reveal that the difference between the dye redox potential and monomer onset oxidation potential plays a crucial role in the PEP kinetics and the doping density of PEDOT HTM. The structure of the dyes, functioning as an electron blocking layer, affects the charge recombination at the TiO2/dye/PEDOT interface. The analysis shows that a donor-n-acceptor dye with well-tuned energy levels and bulky structure results in an in-situ electrochemically doped PEDOT HTM with a high hole conductivity (2.0 S cm(-1)) in sDSCs, leading to efficient dye regeneration and photocharge collection. It is hoped that this work will further encourage research on the future design of new dye molecules for an efficient PEP in order to further enhance the photovoltaic performance of solid-state dye sensitized solar cells.

Keyword
Hole conductor, PEDOT, Dyes, Solar cells
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-279644 (URN)10.1016/j.nanoen.2015.09.010 (DOI)000369565400043 ()
Funder
Swedish Energy Agency, 22191-5StandUpSwedish Research Council, C0482101Knut and Alice Wallenberg Foundation, 2011.0067
Available from: 2016-03-08 Created: 2016-03-02 Last updated: 2016-08-25Bibliographically approved
5. Constructive Effects of Alkyl Chains: A Strategy to Design Simple and Non-Spiro Hole Transporting Materials for High-Efficiency Mixed-Ion Perovskite Solar Cells
Open this publication in new window or tab >>Constructive Effects of Alkyl Chains: A Strategy to Design Simple and Non-Spiro Hole Transporting Materials for High-Efficiency Mixed-Ion Perovskite Solar Cells
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2016 (English)In: ADVANCED ENERGY MATERIALS, ISSN 1614-6832, Vol. 6, no 13, 1502536Article in journal (Refereed) Published
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-300464 (URN)10.1002/aenm.201502536 (DOI)000379314700002 ()
Funder
Swedish Energy AgencyStandUpSwedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Research Council Formas
Available from: 2016-08-09 Created: 2016-08-09 Last updated: 2016-08-25Bibliographically approved
6. Strategy to Boost the Efficiency of Mixed-Ion Perovskite Solar Cells: Changing Geometry of the Hole Transporting Material.
Open this publication in new window or tab >>Strategy to Boost the Efficiency of Mixed-Ion Perovskite Solar Cells: Changing Geometry of the Hole Transporting Material.
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2016 (English)In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 10, no 7, 6816-6825 p.Article in journal (Refereed) Published
Abstract [en]

The hole transporting material (HTM) is an essential component in perovskite solar cells (PSCs) for efficient extraction and collection of the photoinduced charges. Triphenylamine- and carbazole-based derivatives have extensively been explored as alternative and economical HTMs for PSCs. However, the improvement of their power conversion efficiency (PCE), as well as further investigation of the relationship between the chemical structure of the HTMs and the photovoltaic performance, is imperatively needed. In this respect, a simple carbazole-based HTM X25 was designed on the basis of a reference HTM, triphenylamine-based X2, by simply linking two neighboring phenyl groups in a triphenylamine unit through a carbon-carbon single bond. It was found that a lowered highest occupied molecular orbital (HOMO) energy level was obtained for X25 compared to that of X2. Besides, the carbazole moiety in X25 improved the molecular planarity as well as conductivity property in comparison with the triphenylamine unit in X2. Utilizing the HTM X25 in a solar cell with mixed-ion perovskite [HC(NH2)2]0.85(CH3NH3)0.15Pb(I0.85Br0.15)3, a highest reported PCE of 17.4% at 1 sun (18.9% under 0.46 sun) for carbazole-based HTM in PSCs was achieved, in comparison of a PCE of 14.7% for triphenylamine-based HTM X2. From the steady-state photoluminescence and transient photocurrent/photovoltage measurements, we conclude that (1) the lowered HOMO level for X25 compared to X2 favored a higher open-circuit voltage (Voc) in PSCs; (2) a more uniform formation of X25 capping layer than X2 on the surface of perovskite resulted in more efficient hole transport and charge extraction in the devices. In addition, the long-term stability of PSCs with X25 is significantly enhanced compared to X2 due to its good uniformity of HTM layer and thus complete coverage on the perovskite. The results provide important information to further develop simple and efficient small molecular HTMs applied in solar cells.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-300728 (URN)10.1021/acsnano.6b02442 (DOI)000380576600046 ()27304078 (PubMedID)
External cooperation:
Funder
Swedish Energy AgencyStandUpSwedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Research Council Formas
Available from: 2016-08-12 Created: 2016-08-11 Last updated: 2016-09-14Bibliographically approved
7. The Role of 3D Molecular Structural Control in New Hole Transport Materials Outperforming Spiro-OMeTAD in Perovskite Solar Cells
Open this publication in new window or tab >>The Role of 3D Molecular Structural Control in New Hole Transport Materials Outperforming Spiro-OMeTAD in Perovskite Solar Cells
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2016 (English)In: Advanced Energy MaterialsArticle in journal (Refereed) Published
Abstract [en]

This study presents new hole-transport materials (HTMs) to replace the central spiro linkage inspiro-OMeTAD by a CC bond in H11 and CC double bond in H12. This structural change results in a facile synthetic process and a significant change in the molecular geometry. EmployingH11 as HTM in combination with mixed ion perovskite [HC(NH2)2]0.85(CH3NH3)0.15Pb(I0.85Br0.15)3, gives a solar cell power conversion efficiency of 19.8%.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-300736 (URN)10.1002/aenm.201601062 (DOI)
Available from: 2016-08-12 Created: 2016-08-12 Last updated: 2016-08-25

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