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Nonomura, K., Vlachopoulos, N., Unger, E., Häggman, L., Hagfeldt, A. & Boschloo, G. (2019). Blocking the Charge Recombination with Diiodide Radicals by TiO2 Compact Layer in Dye-Sensitized Solar Cells. Journal of the Electrochemical Society, 166(9), B3203-B3208
Open this publication in new window or tab >>Blocking the Charge Recombination with Diiodide Radicals by TiO2 Compact Layer in Dye-Sensitized Solar Cells
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2019 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 166, no 9, p. B3203-B3208Article in journal (Refereed) Published
Abstract [en]

The addition of a compact titanium dioxide (TiO2) layer between the fluorine-doped tin oxide (FTO) coated glass substrate and the mesoporous TiO2 layer in the dye-sensitized solar cell (DSC) based on the iodide/triiodide redox couple (I-/I-3(-)) is known to improve its current-voltage characteristics. The compact layer decreases the recombination of electrons extracted through the FTO layer with I-3(-) around the maximum power point. Furthermore, the short-circuit photocurrent was improved, which previously has been attributed to the improved light transmittance and/or better contact between TiO2 and FTO. Here, we demonstrate that the compact TiO2 layer has another beneficial effect: it blocks the reaction between charge carriers in the FTO and photogenerated diiodide radical species (I-2(-center dot)). Using photomodulated voltammetry, it is demonstrated that the cathodic photocurrent found at bare FTO electrodes is blocked by the addition of a compact TiO2 layer, while the anodic photocurrent due to reaction with I-2(-center dot) is maintained.

Place, publisher, year, edition, pages
ELECTROCHEMICAL SOC INC, 2019
National Category
Physical Chemistry Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-383838 (URN)10.1149/2.0281909jes (DOI)000466839800002 ()
Funder
Swedish Energy AgencySwedish Research Council, 2015-00163Knut and Alice Wallenberg Foundation
Available from: 2019-05-27 Created: 2019-05-27 Last updated: 2019-05-27Bibliographically approved
Boschloo, G. (2019). Improving the Performance of Dye-Sensitized Solar Cells. Frontiers in Chemistry, 7, Article ID 77.
Open this publication in new window or tab >>Improving the Performance of Dye-Sensitized Solar Cells
2019 (English)In: Frontiers in Chemistry, E-ISSN 2296-2646, Vol. 7, article id 77Article in journal (Refereed) Published
Abstract [en]

Dye-sensitized solar cells have been investigated intensively during the last three decades. Nevertheless, there are still many aspects to be explored to further improve their performance. Dye molecules can be modified endlessly for better performance. For instance, steric groups can be introduced to slow down recombination reactions and avoid unfavorable aggregation. There is a need for more optimal dye packing on the mesoporous TiO2 surface to increase light absorption and promote a better blocking effect. Novel redox mediators and HTMs are key elements to reach higher performing DSC as they can offer much higher output voltage than the traditional triiodide/iodide redox couple.

Place, publisher, year, edition, pages
FRONTIERS MEDIA SA, 2019
Keywords
mesoporous TiO2, recombination, electron lifetime, cobalt-complex, maximum power point, organic dyes
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-378375 (URN)10.3389/fchem.2019.00077 (DOI)000458674700001 ()
Funder
StandUp
Available from: 2019-03-07 Created: 2019-03-07 Last updated: 2019-03-07Bibliographically approved
Jain, S. M., Phuyal, D., Davies, M. L., Li, M., Philippe, B., De Castro, C., . . . Durrant, J. R. (2018). An effective approach of vapour assisted morphological tailoring for reducing metal defect sites in lead-free, (CH3NH3)(3)Bi2I9 bismuth-based perovskite solar cells for improved performance and long-term stability. Nano Energy, 49, 614-624
Open this publication in new window or tab >>An effective approach of vapour assisted morphological tailoring for reducing metal defect sites in lead-free, (CH3NH3)(3)Bi2I9 bismuth-based perovskite solar cells for improved performance and long-term stability
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2018 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 49, p. 614-624Article in journal (Refereed) Published
Abstract [en]

We present a controlled, stepwise formation of methylammonium bismuth iodide (CH3NH3)(3)Bi2I9 perovskite films prepared via the vapour assisted solution process (VASP) by exposing BiI3 films to CH3NH3I (MAI) vapours for different reaction times, (CH3NH3)(3)Bi2I9 semiconductor films with tunable optoelectronic properties are obtained. Solar cells prepared on mesoporous TiO2 substrates yielded hysteresis-free efficiencies upto 3.17% with good reproducibility. The good performance is attributed mainly to the homogeneous surface coverage, improved stoichiometry, reduced metallic content in the bulk, and desired optoelectronic properties of the absorbing material. In addition, solar cells prepared using pure BiI3 films without MAI exposure achieved a power conversion efficiency of 0.34%. The non-encapsulated (CH3NH3)(3)Bi2I9 devices were found to be stable for as long as 60 days with only 0.1% drop in efficiency. This controlled formation of (CH3NH3)(3)Bi2I9 perovskite films highlights the benefit of the VASP technique to optimize material stoichiometry, morphology, solar cell performance, and long-term durability.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2018
Keywords
Vapour assisted solution process (VASP), Lead free perovskite, (CH3NH3)(3)Bi2I9, Morphological tailoring, High resolution X-ray photoelectron (HAXPES) spectroscopy
National Category
Materials Chemistry Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-358277 (URN)10.1016/j.nanoen.2018.05.003 (DOI)000434829500071 ()
Funder
Swedish Research CouncilEU, Horizon 2020, 663830
Available from: 2018-08-27 Created: 2018-08-27 Last updated: 2018-10-26Bibliographically approved
Yang, W., Hao, Y., Kloo, L. & Boschloo, G. (2018). Carrier Dynamics of Dye Sensitized-TiO2 in Contact with Different Cobalt Complexes in the Presence of Tri(p-anisyl)amine Intermediates. The Journal of Physical Chemistry C, 122(26), 14345-14354
Open this publication in new window or tab >>Carrier Dynamics of Dye Sensitized-TiO2 in Contact with Different Cobalt Complexes in the Presence of Tri(p-anisyl)amine Intermediates
2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 26, p. 14345-14354Article in journal (Refereed) Published
Abstract [en]

Heterogeneous charge transfer processes at sensitized wide bandgap semiconductor surfaces are imperative for both fundamental knowledge and technical applications. Herein, we focus on the investigation of carrier dynamics of a triphenylamine-based dye, LEG4, sensitized TiO2 (LEG4/TiO2) in contact with two types of electrolyte systems: pure cobalt-based electrolytes and in combination with an organic donor, tri(p-anisyl)amine (TPAA). Four different cobalt redox systems with potentials spanning a 0.3 V range were studied, and the carrier recombination and regeneration kinetics were monitored both at low and at high TiO2 (e(-)) densities (1.3 X 10(18) and 1.3 X 10(19) cm(-3), respectively). The results reveal that the introduction of the TPAA intermediate more effectively suppress the recombination loss of TiO2 (e(-)) under high charge conditions, close to open-circuit, as compared to low charge conditions. As a result, the charge transfer from the cobalt complexes to the oxidized dyes is significantly improved by the addition of TPAA. Dye-sensitized solar cells fabricated with the TPAA-containing electrolytes demonstrate remarkable improvement in both V-OC and J(SC) and lead to more than 25% increase of the light-to-electricity conversion efficiency. Furthermore, an unprecedented detrimental impact of TPAA on the device performance was identified when the redox potential of the TPAA donor and the cobalt complexes are close. This is ascribed to the formation of TPAA(center dot+) which can act as an active recombination centers and thus lower the solar cell performance. These insights point at a strategy to enhance the lifetimes of electrons generated in sensitized semiconductor electrodes by overcoming the charge recombination between TiO2 and the oxidized dye under high carrier densities in the semiconductor substrate and offer practical guidance to the design of future efficient electrolyte systems for dye-sensitized solar cells.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2018
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-361279 (URN)10.1021/acs.jpcc.8b03395 (DOI)000438178900013 ()
Funder
Swedish Research CouncilSwedish Energy AgencyStiftelsen Olle Engkvist Byggmästare
Available from: 2018-09-27 Created: 2018-09-27 Last updated: 2018-09-27Bibliographically approved
Michaels, H., Benesperi, I., Edvinsson, T., Munoz-Garcia, A. B., Pavone, M., Boschloo, G. & Freitag, M. (2018). Copper Complexes with Tetradentate Ligands for Enhanced Charge Transport in Dye-Sensitized Solar Cells. INORGANICS, 6(2), Article ID 53.
Open this publication in new window or tab >>Copper Complexes with Tetradentate Ligands for Enhanced Charge Transport in Dye-Sensitized Solar Cells
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2018 (English)In: INORGANICS, ISSN 2304-6740, Vol. 6, no 2, article id 53Article in journal (Refereed) Published
Abstract [en]

In dye-sensitized solar cells (DSCs), the redox mediator is responsible for the regeneration of the oxidized dye and for the hole transport towards the cathode. Here, we introduce new copper complexes with tetradentate 6,6-bis(4-(S)-isopropyl-2-oxazolinyl)-2,2-bipyridine ligands, Cu(oxabpy), as redox mediators. Copper coordination complexes with a square-planar geometry show low reorganization energies and thus introduce smaller losses in photovoltage. Slow recombination kinetics of excited electrons between the TiO2 and Cu-II(oxabpy) species lead to an exceptionally long electron lifetime, a high Fermi level in the TiO2, and a high photovoltage of 920 mV with photocurrents of 10 mA.cm(-2) and 6.2% power conversion efficiency. Meanwhile, a large driving force remains for the dye regeneration of the Y123 dye with high efficiencies. The square-planar Cu(oxabpy) complexes yield viscous gel-like solutions. The unique charge transport characteristics are attributed to a superposition of diffusion and electronic conduction. An enhancement in charge transport performance of 70% despite the higher viscosity is observed upon comparison of Cu(oxabpy) to the previously reported Cu(tmby)(2) redox electrolyte.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
dye-sensitized solar cell, solar cell, copper complex, redox mediator, electrolyte, tetradentate
National Category
Physical Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-360490 (URN)10.3390/inorganics6020053 (DOI)000436555000018 ()
Funder
Swedish Energy Agency, 42037-1Swedish Energy Agency, 43294-1StandUpCarl Tryggers foundation , 17:158
Available from: 2018-09-17 Created: 2018-09-17 Last updated: 2019-01-15Bibliographically approved
Gotfredsen, H., Neumann, T., Storm, F. E., Munoz, A. V., Jevric, M., Hammerich, O., . . . Nielsen, M. B. (2018). Donor-Acceptor-Functionalized Subphthalocyanines for Dye-Sensitized Solar Cells. CHEMPHOTOCHEM, 2(11), 976-985
Open this publication in new window or tab >>Donor-Acceptor-Functionalized Subphthalocyanines for Dye-Sensitized Solar Cells
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2018 (English)In: CHEMPHOTOCHEM, ISSN 2367-0932, Vol. 2, no 11, p. 976-985Article in journal (Refereed) Published
Abstract [en]

Boron subphthalocyanines (SubPcs) are attractive as light harvesting materials in photovoltaic devices. Here we present the synthesis, optical and electrochemical properties, and device performances of a series of donor-acceptor-functionalized SubPc derivatives incorporating a carboxylic acid for anchoring onto TiO2. Liquid- and solid-state dye-sensitized solar cells (DSCs) were prepared from three compounds, and a triad system consisting of two aniline donor moieties and a benzothiadiazole acceptor moiety was found to exhibit the highest power conversion efficiency (PCE) in the series (PCE=1.54 %; solid-state device). The compounds were prepared by stepwise acetylenic coupling reactions. In addition, we present the synthesis and optical properties of a SubPc derivative incorporating three anilino-substituted 1,1,4,4-tetracyanobutadiene units, prepared by the [2+2] cycloaddition between three ethynyl units at the SubPc periphery and three tetracyanoethylene molecules followed by electrocyclic ring-opening reactions.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2018
Keywords
chromophores, cross-coupling, donor-acceptor systems, macrocycles, solar cells
National Category
Organic Chemistry Physical Chemistry Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-371090 (URN)10.1002/cptc.201800135 (DOI)000449937800005 ()
Available from: 2018-12-19 Created: 2018-12-19 Last updated: 2019-01-15Bibliographically approved
Hao, Y., Yang, W., Karisson, M., Cong, J., Wang, S., Li, X., . . . Boschloo, G. (2018). Efficient Dye-Sensitized Solar Cells with Voltages Exceeding 1 V through Exploring Tris(4-alkoxyphenyl)amine Mediators in Combination with the Tris(bipyridine) Cobalt Redox System. ACS ENERGY LETTERS, 3(8), 1929-1937
Open this publication in new window or tab >>Efficient Dye-Sensitized Solar Cells with Voltages Exceeding 1 V through Exploring Tris(4-alkoxyphenyl)amine Mediators in Combination with the Tris(bipyridine) Cobalt Redox System
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2018 (English)In: ACS ENERGY LETTERS, ISSN 2380-8195, Vol. 3, no 8, p. 1929-1937Article in journal (Refereed) Published
Abstract [en]

Tandem redox electrolytes, prepared by the addition of a tris(p-anisyl)amine mediator into classic tris(bipyridine)cobalt-based electrolytes, demonstrate favorable electron transfer and reduced energy loss in dye-sensitized solar cells. Here, we have successfully explored three tris(4-alkoxyphenyl)-amine mediators with bulky molecular structures and generated more effective tandem redox systems. This series of tandem redox electrolytes rendered solar cells with very high photovoltages exceeding 1 V, which approaches the theoretical voltage limit of tris(bipyridine)cobalt-based electrolytes. Solar cells with power conversion efficiencies of 9.7-11.0% under 1 sun illumination were manufactured. This corresponds to an efficiency improvement of up to 50% as compared to solar cells based on pure tris(bipyridine)cobalt-based electrolytes. The photovoltage increases with increasing steric effects of the tris(4-alkoxyphenyl)amine mediators, which is attributed to a retarded recombination kinetics. These results highlight the importance of structural design for optimized charge transfer at the sensitized semiconductor/electrolyte interface and provide insights for the future development of efficient dye-sensitized solar cells.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-363999 (URN)10.1021/acsenergylett.8b00872 (DOI)000441852800021 ()
Funder
Swedish Energy AgencySwedish Research CouncilKnut and Alice Wallenberg FoundationStiftelsen Olle Engkvist ByggmästareStandUp
Available from: 2018-11-05 Created: 2018-11-05 Last updated: 2018-11-05Bibliographically approved
Yang, L., Schölin, R., Gabrielsson, E., Boschloo, G., Rensmo, H., Sun, L., . . . Johansson, E. M. J. (2018). Experimental and Theoretical Investigation of the Function of 4-tert-Butyl Pyridine for Interface Energy Level Adjustment in Efficient Solid-State Dye-Sensitized Solar Cells. ACS Applied Materials and Interfaces, 10(14), 11572-11579
Open this publication in new window or tab >>Experimental and Theoretical Investigation of the Function of 4-tert-Butyl Pyridine for Interface Energy Level Adjustment in Efficient Solid-State Dye-Sensitized Solar Cells
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2018 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 14, p. 11572-11579Article in journal (Refereed) Published
Abstract [en]

4-tert-Butylpyridine (t-BP) is commonly used in solid state dye-sensitized solar cells (ssDSSCs) to increase the photovoltaic performance. In this report, the mechanism how t-BP functions as a favorable additive is investigated comprehensively. ssDSSCs were prepared with different concentrations of t-BP, and a clear increase in efficiency was observed up to a maximum concentration and for higher concentrations the efficiency thereafter decreases. The energy level alignment in the complete devices was measured using hard X-ray photoelectron spectroscopy (HAXPES). The results show that the energy levels of titanium dioxide are shifted further away from the energy levels of spiro-OMeTAD as the t-BP concentration is increased. This explains the higher photovoltage obtained in the devices with higher t-BP concentration. In addition, the electron lifetime was measured for the devices and the electron lifetime was increased when adding t-BP, which can be explained by the recombination blocking effect at the surface of TiO2. The results from the HAXPES measurements agree with those obtained from density functional theory calculations and give an understanding of the mechanism for the improvement, which is an important step for the future development of solar cells including t-BP.

Keywords
mesoporous, TiO2, photovoltaic, dye, solar energy
National Category
Physical Chemistry Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-353206 (URN)10.1021/acsami.7b16877 (DOI)000430156000021 ()29560716 (PubMedID)
Funder
Swedish Energy AgencySwedish Research CouncilSwedish Research Council FormasEU, FP7, Seventh Framework Programme, 226716
Available from: 2018-06-13 Created: 2018-06-13 Last updated: 2018-06-13Bibliographically approved
Jacobsson, J., Svanström, S., Andrei, V., Rivett, J. P. H., Kornienko, N., Philippe, B., . . . Boschloo, G. (2018). Extending the Compositional Space of Mixed Lead Halide Perovskites by Cs, Rb, K, and Na Doping. The Journal of Physical Chemistry C, 122(25), 13548-13557
Open this publication in new window or tab >>Extending the Compositional Space of Mixed Lead Halide Perovskites by Cs, Rb, K, and Na Doping
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2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 25, p. 13548-13557Article in journal (Refereed) Published
Abstract [en]

A trend in high performing lead halide perovskite solar cell devices has been increasing compositional complexity by successively introducing more elements, dopants, and additives into the structure; and some of the latest top efficiencies have been achieved with a quadruple cation mixed halide perovskite Cs(x)FA(y)MA(z)Rb(1-x-y-z)PbBr(q)I(3-9). This paper continues this trend by exploring doping of mixed lead halide perovskites, FA(0.83)MA(0.17)PbBr(0.51)I(2.49), with an extended set of alkali cations, i.e., Cs+, Rb+, K+, and Na+, as well as combinations of them. The doped perovskites were investigated with X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy, hard X-ray photoelectron spectroscopy, UV-vis, steady state fluorescence, and ultrafast transient absorption spectroscopy. Solar cell devices were made as well. Cs+ can replace the organic cations in the perovskite structure, but Rb+, K+, and Na+ do not appear to do that. Despite this, samples doped with K and Na have substantially longer fluorescence lifetimes, which potentially could be beneficial for device performance.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2018
National Category
Physical Chemistry Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-361115 (URN)10.1021/acs.jpcc.7b12464 (DOI)000437811500039 ()
Funder
Swedish Energy Agency, P43294-1Swedish Foundation for Strategic Research , RMA15-0130
Available from: 2018-09-21 Created: 2018-09-21 Last updated: 2019-02-18Bibliographically approved
Zhang, X., Zhang, J., Phuyal, D., Du, J., Tian, L., Öberg, V. A., . . . Johansson, E. M. J. (2018). Inorganic CsPbI3 Perovskite Coating on PbS Quantum Dot for Highly Efficient and Stable Infrared Light Converting Solar Cells. Advanced Energy Materials, 8(6), Article ID 1702049.
Open this publication in new window or tab >>Inorganic CsPbI3 Perovskite Coating on PbS Quantum Dot for Highly Efficient and Stable Infrared Light Converting Solar Cells
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2018 (English)In: Advanced Energy Materials, ISSN 1614-6832, Vol. 8, no 6, article id 1702049Article in journal (Refereed) Published
Abstract [en]

Solution-processed colloidal quantum dot (CQD) solar cells harvesting the infrared part of the solar spectrum are especially interesting for future use in semitransparent windows or multilayer solar cells. To improve the device power conversion efficiency (PCE) and stability of the solar cells, surface passivation of the quantum dots is vital in the research of CQD solar cells. Herein, inorganic CsPbI3 perovskite (CsPbI3-P) coating on PbS CQDs with a low-temperature, solution-processed approach is reported. The PbS CQD solar cell with CsPbI3-P coating gives a high PCE of 10.5% and exhibits remarkable stability both under long-term constant illumination and storage under ambient conditions. Detailed characterization and analysis reveal improved passivation of the PbS CQDs with the CsPbI3-P coating, and the results suggest that the lattice coherence between CsPbI3-P and PbS results in epitaxial induced growth of the CsPbI3-P coating. The improved passivation significantly diminishes the sub-bandgap trap-state assisted recombination, leading to improved charge collection and therefore higher photovoltaic performance. This work therefore provides important insight to improve the CQD passivation by coating with an inorganic perovskite ligand for photovoltaics or other optoelectronic applications.

Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH, 2018
Keywords
charge recombination, inorganic perovskite, quantum dots, solar cells, surface passivation
National Category
Physical Chemistry Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-348982 (URN)10.1002/aenm.201702049 (DOI)000426152400017 ()
Funder
Swedish Energy AgencySwedish Research CouncilSwedish Research Council Formas
Available from: 2018-04-26 Created: 2018-04-26 Last updated: 2018-10-26Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-8249-1469

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