| 1. |
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| 2. |
- Johansson, Erik M .J., et al.
(författare)
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Interfacial properties of photovoltaic TiO2/dye/PEDOT-PSS heterojunctions
- 2005
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Ingår i: Synthetic metals. - : Elsevier BV. - 0379-6779 .- 1879-3290. ; 149:03-feb, s. 157-167
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Tidskriftsartikel (refereegranskat)abstract
- Systems comprising a dense TiO2 film electrode, a ruthenium polypyridine dye and a PEDOT-PSS (poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulphonate)) film were prepared. The heterojunctions were shown to have photovoltaic properties, with the dye absorbing the light, the TiO2 acting as an electron conducting material and PEDOT-PSS acting as a hole transport material. A series of dyes was used to investigate their influence on the photocurrent and the photovoltage characteristics of the heterojunction. These results were compared to a photoelectrochemical system in which the PEDOT-PSS was replaced by a liquid electrolyte containing triiodide/iodide redox-couple. Photoelectron spectroscopy (PES) was used to monitor the interfacial properties of the heterojunction and the investigation points out effects of importance when assembling the materials together to a functional unit. Specifically, it was concluded that the interaction with the dye clearly affects the structure of PEDOT-PSS, both with respect to the surface composition of PSS relative to PEDOT and with respect to the chemical state of the sulphur in the polymers. Moreover, a comparison of the Ru3d and the valence band spectra of the two different interfaces (dye/TiO2 and dye/PEDOT-PSS) indicates that the energy level structure of the dyes compared to the substrate is different for the two surfaces. Thus, in the combined energy level picture under dark conditions, the energy levels in TiO2 relative to the energy levels in PEDOT-PSS depend on the dye.
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| 3. |
- Westermark, Karin, et al.
(författare)
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Determination of the electronic density of states at a nanostructured TiO2/Ru-dye/electrolyte interface by means of photoelectron spectroscopy
- 2002
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Ingår i: Chemical Physics. - 0301-0104 .- 1873-4421. ; 285:1, s. 157-165
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Tidskriftsartikel (refereegranskat)abstract
- In this work, photoelectron spectroscopy is used to measure the electronic density of states in the band gap region of a nanostructured TiO2 film. Such nanostructured films are used in dye-sensitized solar cells, and in this study a plain TiO2 film as well as a dye-sensitized film were examined. Further, to simulate the electrolyte effect on the energy levels at the oxide/dye/electrolyte interface in a solar cell, the density of states in the band gap region for an electrochemically prepared TiO2 film inserted with Li+ ions was measured. From the experimental findings we discuss the distribution and chemical nature of electron trap states in the band gap and the energy matching between the LUMO level of the adsorbed dye, cis-bis(4,4′-dicarboxy-2,2′-bipyridine)-bis(isothiocyanato)ruthenium(II), and the TiO2 conduction band edge.
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| 4. |
- Agrell, H. G., et al.
(författare)
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Conductivity studies of nanostructured TiO2 films permeated with electrolyte
- 2004
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 108:33, s. 12388-12396
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Tidskriftsartikel (refereegranskat)abstract
- Charge transport in nanostructured TiO2 films permeated with an electrolyte was studied, using temperature-dependent conductivity and electron accumulation measurements. Two regions for charge transport were distinguished from the relationship between conductivity and electron concentration. In the first region (similar to1-20 electrons per TiO2 particle), the effective electron mobility is dependent on the electron concentration and values between 7 x 10(-4) and 78 x 10(-4) cm(2) V-1 s(-1) were determined. The activation energy of the mobility was similar to0.3 eV. The charge transport can be described with a trapping/detrapping model that involves localized band-gap states. In the second region (> 20 electrons per TiO2 particle), the effective electron mobility is independent of electron concentration and values of similar to150 x 10(-4) cm(2) V-1 s(-1) are calculated. The activation energy of mobility is in the range of 0-0.15 eV, depending on the electrolyte. Transport of electrons in the conduction band seems to be the most applicable model.
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| 5. |
- Agrios, Alexander G., et al.
(författare)
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Low-temperature TiO2 Films for Dye-sensitized Solar Cells : Factors Affecting Energy Conversion Efficiency
- 2008
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:27, s. 10021-10026
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor films prepd. by electrostatic layer-by-layer deposition can be used to fabricate dye-sensitized solar cells after low-temp. treatment (150 DegC). However, the resulting photocurrent is much less than when the film is sintered at 500 DegC. The difference in short-circuit current is a factor of 2.2 with the Ru-based dye N719 and is 3.5 with the org. dye D5. The photocurrent at a given wavelength is proportional to the light-harvesting efficiency, charge injection effciency, and charge collection efficiency. Sintered films take up more than 60% more of either dye than unsintered films and therefore absorb more photons. Electron injection is hindered in unsintered films due to a conduction band edge potential 100 mV more neg. than in a sintered electrode. Addnl. injection effects could be due to adsorption of the dye to polymer rather than to TiO2 in unsintered films, although our measurements were inconclusive on this point. Kinetic studies show electron transport times (ttr) an order of magnitude faster then electron lifetimes (te) in both sintered and unsintered electrodes. Furthermore, a Li+ insertion expt. shows that both films have good elec. connectivity between TiO2 nanoparticles. Unsintered films thus exhibit efficient charge transport despite the presence of polymer and the lack of heat treatment to induce necking.
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| 6. |
- Ahlawat, Paramvir, et al.
(författare)
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A combined molecular dynamics and experimental study of two-step process enabling low-temperature formation of phase-pure alpha-FAPbI3
- 2021
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:17
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Tidskriftsartikel (refereegranskat)abstract
- It is well established that the lack of understanding the crystallization process in a two-step sequential deposition has a direct impact on efficiency, stability, and reproducibility of perovskite solar cells. Here, we try to understand the solid-solid phase transition occurring during the two-step sequential deposition of methylammonium lead iodide and formamidinium lead iodide. Using metadynamics, x-ray diffraction, and Raman spectroscopy, we reveal the microscopic details of this process. We find that the formation of perovskite proceeds through intermediate structures and report polymorphs found for methylammonium lead iodide and formamidinium lead iodide. From simulations, we discover a possible crystallization pathway for the highly efficient metastable alpha phase of formamidinium lead iodide. Guided by these simulations, we perform experiments that result in the low-temperature crystallization of phase-pure alpha-formamidinium lead iodide.
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| 7. |
- Aitola, Kerttu, et al.
(författare)
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Carbon nanotube-based hybrid hole-transporting material and selective contact for high efficiency perovskite solar cells
- 2016
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Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 9:2, s. 461-466
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a high efficiency perovskite solar cell with a hybrid hole-transporting material-counter electrode based on a thin single-walled carbon nanotube (SWCNT) film and a drop-cast 2,2,7,-7-tetrakis(N, N-di-p-methoxyphenylamine)-9,90-spirobifluorene (Spiro-OMeTAD) hole-transporting material (HTM). The average efficiency of the solar cells was 13.6%, with the record cell yielding 15.5% efficiency. The efficiency of the reference solar cells with spin-coated Spiro-OMeTAD hole-transportingmaterials (HTMs) and an evaporated gold counter electrode was 17.7% (record 18.8%), that of the cells with only a SWCNT counter electrode (CE) without additional HTM was 9.1% (record 11%) and that of the cells with gold deposited directly on the perovskite layer was 5% (record 6.3%). Our results show that it is possible to manufacture high efficiency perovskite solar cells with thin film (thickness less than 1 mu m) completely carbon-based HTMCEs using industrially upscalable manufacturing methods, such as press-transferred CEs and drop-cast HTMs.
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| 8. |
- Aitola, Kerttu, et al.
(författare)
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Carbon nanotube film replacing silver in high-efficiency solid-state dye solar cells employing polymer hole conductor
- 2015
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Ingår i: Journal of Solid State Electrochemistry. - : Springer Science and Business Media LLC. - 1432-8488 .- 1433-0768. ; 19:10, s. 3139-3144
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Tidskriftsartikel (refereegranskat)abstract
- A semitransparent, flexible single-walled carbon nanotube (SWCNT) film was efficiently used in place of evaporated silver as the counter electrode of a poly(3,4-ethylenedioxythiophene) polymer-based solid-state dye solar cell (SSDSC): the solar-to-electrical energy conversion efficiency of the SWCNT-SSDSC was 4.8 % when it was 5.2 % for the Ag-SSDSC. The efficiency difference stemmed from a 0.1-V difference in the open-circuit voltage, whose reason was speculated to be related to the different recombination processes in the two types of SSDSCs.
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| 9. |
- Aitola, Kerttu, et al.
(författare)
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High Temperature-Stable Perovskite Solar Cell Based on Low-Cost Carbon Nanotube Hole Contact
- 2017
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Ingår i: Advanced Materials. - : Wiley-VCH Verlagsgesellschaft. - 0935-9648 .- 1521-4095. ; 29:17
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Tidskriftsartikel (refereegranskat)abstract
- Mixed ion perovskite solar cells (PSC) are manufactured with a metal-free hole contact based on press-transferred single-walled carbon nanotube (SWCNT) film infiltrated with 2,2,7,-7-tetrakis(N, N-di-p-methoxyphenylamine)-9,90-spirobifluorene (Spiro-OMeTAD). By means of maximum power point tracking, their stabilities are compared with those of standard PSCs employing spin-coated Spiro-OMeTAD and a thermally evaporated Au back contact, under full 1 sun illumination, at 60 degrees C, and in a N-2 atmosphere. During the 140 h experiment, the solar cells with the Au electrode experience a dramatic, irreversible efficiency loss, rendering them effectively nonoperational, whereas the SWCNT-contacted devices show only a small linear efficiency loss with an extrapolated lifetime of 580 h.
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| 10. |
- Aitola, Kerttu, et al.
(författare)
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Highly catalytic carbon nanotube counter electrode on plastic for dye solar cells utilizing cobalt-based redox mediator
- 2013
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 111, s. 206-209
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Tidskriftsartikel (refereegranskat)abstract
- A flexible, slightly transparent and metal-free random network of single-walled carbon nanotubes (SWCNTs) on plain polyethylene terephthalate (PET) plastic substrate outperformed platinum on conductive glass and on plastic as the counter electrode (CE) of a dye solar cell employing a Co(II/III)tris(2,2'-bipyridyl) complex redox mediator in 3-methoxypropionitrile solvent. The CE charge-transfer resistance of the SWCNT film was 0.60 Omega cm(2), 4.0 Omega cm(2) for sputtered platinum on indium tin oxide-PET substrate and 1.7 Omega cm(2) for thermally deposited Pt on fluorine-doped tin oxide glass, respectively. The solar cell efficiencies were in the same range, thus proving that an entirely carbon-based SWCNT film on plastic is as good CE candidate for the Co electrolyte. (C) 2013 Elsevier Ltd. All rights reserved.
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