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Melianas, Armantas
Publications (10 of 12) Show all publications
Melianas, A., Pranculis, V., Spoltore, D., Benduhn, J., Inganäs, O., Gulbinas, V., . . . Kemerink, M. (2017). Charge Transport in Pure and Mixed Phases in Organic Solar Cells. Advanced Energy Materials, 7(20)
Open this publication in new window or tab >>Charge Transport in Pure and Mixed Phases in Organic Solar Cells
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2017 (English)In: Advanced Energy Materials, ISSN 1614-6840, Vol. 7, no 20Article in journal (Refereed) Published
Abstract [en]

In organic solar cells continuous donor and acceptor networks are considered necessary for charge extraction, whereas discontinuous neat phases and molecularly mixed donor–acceptor phases are generally regarded as detrimental. However, the impact of different levels of domain continuity, purity, and donor–acceptor mixing on charge transport remains only semiquantitatively described. Here, cosublimed donor–acceptor mixtures, where the distance between the donor sites is varied in a controlled manner from homogeneously diluted donor sites to a continuous donor network are studied. Using transient measurements, spanning from sub-picoseconds to microseconds photogenerated charge motion is measured in complete photovoltaic devices, to show that even highly diluted donor sites (5.7%–10% molar) in a buckminsterfullerene matrix enable hole transport. Hopping between isolated donor sites can occur by long-range hole tunneling through several buckminsterfullerene molecules, over distances of up to ≈4 nm. Hence, these results question the relevance of “pristine” phases and whether a continuous interpenetrating donor–acceptor network is the ideal morphology for charge transport.

Place, publisher, year, edition, pages
John Wiley & Sons, 2017
Keywords
charge carrier transport, fullerene domains, low donor concentration, organic photovoltaics, tunneling
National Category
Physical Chemistry Condensed Matter Physics Biophysics Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Identifiers
urn:nbn:se:liu:diva-139690 (URN)10.1002/aenm.201700888 (DOI)000413695300018 ()
Note

Funding agencies: German Federal Ministry for Education and Research (BMBF) through the InnoProfille project "Organische p-i-n Bauelemente 2.2"; Research Council of Lithuania [MIP-85/2015]; Science Council of Sweden; Knut and Alice Wallenberg foundation; Wallenberg Scholar

Available from: 2017-08-09 Created: 2017-08-09 Last updated: 2017-11-13Bibliographically approved
Melianas, A. (2017). Non-Equilibrium Charge Motion in Organic Solar Cells. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Non-Equilibrium Charge Motion in Organic Solar Cells
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Organic photovoltaic (OPV) devices based on semiconducting polymers and small molecules allow for a low cost alternative to inorganic solar cells. Recent developments show power conversion efficiencies as high as 10-12%, highlighting the potential of this technology. Nevertheless, further improvements are necessary to achieve commercialization.

To a large extent the performance of these devices is dictated by their ability to extract the photo-generated charge, which is related to the charge carrier mobility. Various time-resolved and steady-state techniques are available to probe the charge carrier mobility in OPVs but often lead to different mobility values for one and the same system. Despite such conflicting observations it is generally assumed that charge transport in OPV devices can be described by well-defined charge carrier mobilities, typically obtained using a single steady-state technique. This thesis shows that the relevance of such well-defined mobilities for the charge separation and extraction processes is very limited.

Although different transient techniques probe different time scales after photogeneration, they are mutually consistent as they probe the same physical mechanism governing charge motion – gradual thermalization of the photo-generated carriers in the disorder broadened density of states (DOS). The photo-generated carriers gradually lose their excess energy during transport to the extracting electrodes, but not immediately. Typically not all excess energy is dissipated as the photo-generated carriers tend to be extracted from the OPV device before reaching quasi-equilibrium.

Carrier motion is governed by thermalization, leading to a time-dependent carrier mobility that is significantly higher than the steady-state mobility. This picture is confirmed by several transient techniques: Time-resolved Terahertz Spectroscopy (TRTS), Time-resolved Microwave Conductance (TRMC) combined with Transient Absorption (TA), electrical extraction of photo-induced charges (photo-CELIV). The connection between transient and steady-state mobility measurements (space-charge limited conductivity, SCLC) is described. Unification of transient opto-electric techniques to probe charge motion in OPVs is presented.

Using transient experiments the distribution of extraction times of photo-generated charges in an operating OPV device has been determined and found to be strongly dispersive, spanning several decades in time. In view of the strong dispersion in extraction times the relevance of even a well-defined time-dependent mean mobility is limited.

In OPVs a continuous ‘percolating’ donor network is often considered necessary for efficient hole extraction, whereas if the network is discontinuous, hole transport is thought to deteriorate significantly, limiting device performance. Here, it is shown that even highly diluted donor sites (5.7-10 %) in a buckminsterfullerene (C60) matrix enable reasonably efficient hole transport. Using transient measurements it is demonstrated that hole transport between isolated donor sites can occur by long-range hole tunneling (over distances of ~4 nm) through several C60 molecules – even a discontinuous donor network enables hole transport

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. p. 83
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1836
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-136479 (URN)10.3384/diss.diva-136479 (DOI)9789176855638 (ISBN)
Public defence
2017-05-19, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2017-04-18 Created: 2017-04-13 Last updated: 2017-08-09Bibliographically approved
Bergqvist, J., Tress, W., Forchheimer, D., Melianas, A., Tang, Z., Haviland, D. & Inganäs, O. (2016). New method for lateral mapping of bimolecular recombination in thin film organic solar cells. Progress in Photovoltaics, 24(8), 1096-1108
Open this publication in new window or tab >>New method for lateral mapping of bimolecular recombination in thin film organic solar cells
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2016 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 24, no 8, p. 1096-1108Article in journal (Refereed) Published
Abstract [en]

The best organic solar cells are limited by bimolecular recombination. Tools to study these losses are available; however, they are only developed for small area (laboratory-scale) devices and are not yet available for large area (production-scale) devices. Here we introduce the Intermodulation Light Beam-Induced Current (IMLBIC) technique, which allows simultaneous spatial mapping of both the amount of extracted photocurrent and the bimolecular recombination over the active area of a solar cell. We utilize the second-order non-linear dependence on the illumination intensity as a signature for bimolecular recombination. Using two lasers modulated with different frequencies, we record the photocurrent response at each modulation frequency and the bimolecular recombination in the second-order intermodulation response at the sum and difference of the two frequencies. Drift-diffusion simulations predict a unique response for different recombination mechanisms. We successfully verify our approach by studying solar cells known to have mainly bimolecular recombination and thus propose this method as a viable tool for lateral detection and characterization of the dominant recombination mechanisms in organic solar cells. We expect that IMLBIC will be an important future tool for characterization and detection of recombination losses in large area organic solar cells.

Place, publisher, year, edition, pages
John Wiley & Sons, 2016
Keywords
Organic photovoltaics, imaging, photocurrent, bimolecular recombination, light beam induced current, LBIC, intermodulation
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-123033 (URN)10.1002/pip.2770 (DOI)000380164100007 ()
Note

Funding agencies|Swedish Research Council; Swedish Energy Agency; the Knut and Alice Wallenberg foundation through a Wallenberg Scholar grant to O.I

At the time for thesis presentation publication was in status: Manuscript

Available from: 2015-12-02 Created: 2015-12-02 Last updated: 2017-12-01Bibliographically approved
Tang, Z., Liu, B., Melianas, A., Bergqvist, J., Tress, W., Bao, Q., . . . Zhang, F. (2015). A New Fullerene-Free Bulk-Heterojunction System for Efficient High-Voltage and High-Fill Factor Solution-Processed Organic Photovoltaics. Advanced Materials, 27(11), 1900-+
Open this publication in new window or tab >>A New Fullerene-Free Bulk-Heterojunction System for Efficient High-Voltage and High-Fill Factor Solution-Processed Organic Photovoltaics
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2015 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 27, no 11, p. 1900-+Article in journal (Refereed) Published
Abstract [en]

Small molecule donor/polymer acceptor bulk-heterojunction films with both compounds strongly absorbing have great potential for further enhancement of the performance of organic solar cells. By employing a newly synthesized small molecule donor with a commercially available polymer acceptor in a solution-processed fullerene-free system, a high power conversion efficiency of close to 4% is reported.

Place, publisher, year, edition, pages
Wiley-VCH Verlag, 2015
National Category
Biological Sciences Physical Sciences
Identifiers
urn:nbn:se:liu:diva-116947 (URN)10.1002/adma.201405485 (DOI)000351216500012 ()25645709 (PubMedID)
Note

Funding Agencies|Swedish Energy Agency; Knut and Alice Wallenberg foundation; Swedish research council (VR); Chinese scholarship council

Available from: 2015-04-10 Created: 2015-04-10 Last updated: 2017-12-04
Kroon, R., Melianas, A., Zhuang, W., Bergqvist, J., Diaz de Zerio Mendaza, A., Steckler, T. T., . . . Andersson, M. R. (2015). Comparison of selenophene and thienothiophene incorporation into pentacyclic lactam-based conjugated polymers for organic solar cells. Polymer Chemistry, 6(42), 7402-7409
Open this publication in new window or tab >>Comparison of selenophene and thienothiophene incorporation into pentacyclic lactam-based conjugated polymers for organic solar cells
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2015 (English)In: Polymer Chemistry, ISSN 1759-9954, E-ISSN 1759-9962, Vol. 6, no 42, p. 7402-7409Article in journal (Refereed) Published
Abstract [en]

In this work, we compare the effect of incorporating selenophene versus thienothiophene spacers into pentacyclic lactam-based conjugated polymers for organic solar cells. The two cyclic lactam-based copolymers were obtained via a new synthetic method for the lactam moiety. Selenophene incorporation results in a broader and red-shifted optical absorption while retaining a deep highest occupied molecular orbital level, whereas thienothienophene incorporation results in a blue-shifted optical absorption. Additionally, grazing-incidence wide angle X-ray scattering data indicates edge- and face-on solid state order for the selenophene-based polymer as compared to the thienothiophene-based polymer, which orders predominantly edge-on with respect to the substrate. In polymer : PC71BM bulk heterojunction solar cells both materials show a similar open-circuit voltage of similar to 0.80-0.84 V, however the selenophene-based polymer displays a higher fill factor of similar to 0.70 vs. similar to 0.65. This is due to the partial face-on backbone orientation of the selenophene-based polymer, leading to a higher hole mobility, as confirmed by single-carrier diode measurements, and a concomitantly higher fill factor. Combined with improved spectral coverage of the selenophene-based polymer, as confirmed by quantum efficiency experiments, it offers a larger short-circuit current density of similar to 12 mA cm(-2). Despite the relatively low molecular weight of both materials, a very robust power conversion efficiency similar to 7% is achieved for the selenophene-based polymer, while the thienothiophene-based polymer demonstrates only a moderate maximum PCE of similar to 5.5%. Hence, the favorable effects of selenophene incorporation on the photovoltaic performance of pentacyclic lactam-based conjugated polymers are clearly demonstrated.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2015
National Category
Biological Sciences
Identifiers
urn:nbn:se:liu:diva-122675 (URN)10.1039/c5py01245g (DOI)000363214600007 ()
Note

Funding Agencies|Chalmers Areas of Advance Materials Science, Energy and Nanoscience and Nanotechnology; Swedish Research Council; Knut and Alice Wallenberg foundation; Swedish Energy Agency; South Australian government; NSF; NIH/NIGMS via NSF [DMR-1332208]

Available from: 2015-11-16 Created: 2015-11-13 Last updated: 2017-12-01
Tang, Z., Elfwing, A., Melianas, A., Bergqvist, J., Bao, Q. & Inganäs, O. (2015). Fully-solution-processed organic solar cells with a highly efficient paper-based light trapping element. Journal of Materials Chemistry A, 3(48), 24289-24296
Open this publication in new window or tab >>Fully-solution-processed organic solar cells with a highly efficient paper-based light trapping element
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2015 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 48, p. 24289-24296Article in journal (Refereed) Published
Abstract [en]

We demonstrate the use of low cost paper as an efficient light-trapping element for thin film photovoltaics. We verify its use in fully-solution processed organic photovoltaic devices with the highest power conversion efficiency and the lowest internal electrical losses reported so far, the architecture of which - unlike most of the studied geometries to date - is suitable for upscaling, i.e. commercialization. The use of the paper-reflector enhances the external quantum efficiency (EQE) of the organic photovoltaic device by a factor of approximate to 1.5-2.5 over the solar spectrum, which rivals the light harvesting efficiency of a highly-reflective but also considerably more expensive silver mirror back-reflector. Moreover, by detailed theoretical and experimental analysis, we show that further improvements in the photovoltaic performance of organic solar cells employing PEDOT:PSS as both electrodes rely on the future development of high-conductivity and high-transmittance PEDOT:PSS. This is due optical losses in the PEDOT:PSS electrodes.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2015
National Category
Biological Sciences Physical Sciences
Identifiers
urn:nbn:se:liu:diva-123845 (URN)10.1039/c5ta07154b (DOI)000366163000014 ()
Note

Funding Agencies|Swedish Energy Agency; Knut and Alice Wallenberg Foundation through a Wallenberg Scholar grant; Knut and Alice Wallenberg Foundation through the project Power Papers

Available from: 2016-01-11 Created: 2016-01-11 Last updated: 2017-12-01
Diaz de Zerio Mendaza, A., Melianas, A., Rossbauer, S., Backe, O., Nordstierna, L., Erhart, P., . . . Muller, C. (2015). High-Entropy Mixtures of Pristine Fullerenes for Solution-Processed Transistors and Solar Cells. Advanced Materials, 27(45), 7325
Open this publication in new window or tab >>High-Entropy Mixtures of Pristine Fullerenes for Solution-Processed Transistors and Solar Cells
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2015 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 27, no 45, p. 7325-Article in journal (Refereed) Published
Abstract [en]

The solubility of pristine fullerenes can be enhanced by mixing C-60 and C-70 due to the associated increase in configurational entropy. This "entropic dissolution" allows the preparation of field-effect transistors with an electron mobility of 1 cm(2) V-1 s(-1) and polymer solar cells with a highly reproducible power-conversion efficiency of 6%, as well as a thermally stable active layer.

Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH, 2015
National Category
Biological Sciences
Identifiers
urn:nbn:se:liu:diva-124496 (URN)10.1002/adma.201503530 (DOI)000367833200008 ()26460821 (PubMedID)
Note

Funding Agencies|Swedish Research Council, Formas; Chalmers Area of Advance Energy; Knut and Alice Wallenberg Foundation through two Wallenberg Academy Fellowships; European Research Council (ERC) [637624]

Available from: 2016-02-02 Created: 2016-02-01 Last updated: 2017-11-30
Melianas, A., Etzold, F., Savenije, T. J., Laquai, F., Inganäs, O. & Kemerink, M. (2015). Photo-generated carriers lose energy during extraction from polymer-fullerene solar cells. Nature Communications, 6(8778)
Open this publication in new window or tab >>Photo-generated carriers lose energy during extraction from polymer-fullerene solar cells
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2015 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, no 8778Article in journal (Refereed) Published
Abstract [en]

In photovoltaic devices, the photo-generated charge carriers are typically assumed to be in thermal equilibrium with the lattice. In conventional materials, this assumption is experimentally justified as carrier thermalization completes before any significant carrier transport has occurred. Here, we demonstrate by unifying time-resolved optical and electrical experiments and Monte Carlo simulations over an exceptionally wide dynamic range that in the case of organic photovoltaic devices, this assumption is invalid. As the photo-generated carriers are transported to the electrodes, a substantial amount of their energy is lost by continuous thermalization in the disorder broadened density of states. Since thermalization occurs downward in energy, carrier motion is boosted by this process, leading to a time-dependent carrier mobility as confirmed by direct experiments. We identify the time and distance scales relevant for carrier extraction and show that the photo-generated carriers are extracted from the operating device before reaching thermal equilibrium.

Place, publisher, year, edition, pages
Nature Publishing Group, 2015
National Category
Biological Sciences Physical Sciences
Identifiers
urn:nbn:se:liu:diva-123824 (URN)10.1038/ncomms9778 (DOI)000366294700004 ()26537357 (PubMedID)
Note

Funding Agencies|Swedish Science Council and Energimyndigheten; Knut and Alice Wallenberg foundation; Deutsche Forschungsgemeinschaft [SPP1355]

Available from: 2016-01-11 Created: 2016-01-11 Last updated: 2017-12-01
Bergqvist, J., Melianas, A., Andersson, O., Lindqvist, C., Musumeci, C. & Inganäs, O. (2015). Time-resolved morphology formation of solution cast polymer: fullerene blends revealed by in-situ photoluminescence spectroscopy.
Open this publication in new window or tab >>Time-resolved morphology formation of solution cast polymer: fullerene blends revealed by in-situ photoluminescence spectroscopy
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2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

The nanoscale morphology of the photo-active layer in organic solar cells is critical for device efficiency. The photoactive layer is cast from solution and during drying both the polymer and the fullerene self-assemble to form a blend. Here, we introduce in-situ spectroscopic photoluminescence (PL) combined with laser reflectometry to monitor the drying process of an amorphous polymer:fullerene blend. When casting only the pristine components (polymer or PCBM only), the strength of PL emission is proportional to the solid content of the drying solution, and both kinetics reveal a rapid aggregation onset at the final stage of film drying. On the contrary, when casting polymer:fullerene blends, the strength of PL emission is proportional to the wet film thickness and reveals polymer/fullerene charge transfer (CT) already at the earliest stages of film drying, i.e. in dilute solutions. The proposed method allows to detect polymer/fullerene phase separation during film casting – from a reduction in the PL quenching rate as the film dries. Poor solvents lead to phase separation already at early stages of film drying (low solid content), resulting in a coarse final morphology as confirmed by atomic force microscopy (AFM). We therefore anticipate that the proposed method will be an important tool in the future development of processing inks, not only for solution-cast polymer:fullerene solar cells but also for organic heterojunctions in general.

National Category
Physical Sciences Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-123032 (URN)
Available from: 2015-12-02 Created: 2015-12-02 Last updated: 2015-12-03
Melianas, A., Pranculis, V., Devižis, A., Gulbinas, V., Inganäs, O. & Kemerink, M. (2014). Dispersion-Dominated Photocurrent in Polymer:Fullerene Solar Cells. Advanced Functional Materials, 24(28), 4507-4514
Open this publication in new window or tab >>Dispersion-Dominated Photocurrent in Polymer:Fullerene Solar Cells
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2014 (English)In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 24, no 28, p. 4507-4514Article in journal (Refereed) Published
Abstract [en]

Organic bulk heterojunction solar cells are often regarded as near-equilibrium devices, whose kinetics are set by well-defined charge carrier mobilities, and relaxation in the density of states is commonly ignored or included purely phenomenologically. Here, the motion of photocreated charges is studied experimentally with picosecond time resolution by a combination of time-resolved optical probing of electric field and photocurrent measurements, and the data are used to define parameters for kinetic Monte Carlo modelling. The results show that charge carrier motion in a prototypical polymer:fullerene solar cell under operational conditions is orders of magnitude faster than would be expected on the basis of corresponding near-equilibrium mobilities, and is extremely dispersive. There is no unique mobility. The distribution of extraction times of photocreated charges in operating organic solar cells can be experimentally determined from the charge collection transients measured under pulsed excitation. Finally, a remarkable distribution of the photocurrent over energy is found, in which the most relaxed charge carriers in fact counteract the net photocurrent.

Place, publisher, year, edition, pages
Weinheim, Germany: Wiley-VCH Verlagsgesellschaft, 2014
Keywords
solar cell; organic solar cell; dispersion; photocurrent; charge carrier relaxation; Monte Carlo simulations
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-108324 (URN)10.1002/adfm.201400404 (DOI)000339713900015 ()
Note

Funding agencies|Swedish Science Council (VR); Swedish Energy Agency; Knut and Alice Wallenberg foundation; European Social Fund under Global Grant measure

Available from: 2014-06-26 Created: 2014-06-26 Last updated: 2017-12-05Bibliographically approved
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