| 61. |
- Bergqvist, Jonas, et al.
(författare)
-
New method for lateral mapping of bimolecular recombination in thin-film organic solar cells
- 2016
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Ingår i: Progress in Photovoltaics. - : John Wiley & Sons. - 1062-7995 .- 1099-159X. ; 24:8, s. 1096-1108
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 62. |
- Bergqvist, Jonas, et al.
(författare)
-
Sub-glass transition annealing enhances polymer solar cell performance
- 2014
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488. ; 2:17, s. 6146-6152
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Tidskriftsartikel (refereegranskat)abstract
- Thermal annealing of non-crystalline polymer: fullerene blends typically results in a drastic decrease in solar cell performance. In particular aggressive annealing above the glass transition temperature results in a detrimental coarsening of the blend nanostructure. We demonstrate that mild annealing below the glass transition temperature is a viable avenue to control the nanostructure of a non-crystalline thiophene-quinoxaline copolymer: fullerene blend. Direct imaging methods indicate that coarsening of the blend nanostructure can be avoided. However, a combination of absorption and luminescence spectroscopy reveals that local changes in the polymer conformation as well as limited fullerene aggregation are permitted to occur. As a result, we are able to optimise the solar cell performance evenly across different positions of the coated area, which is a necessary criterion for large-scale, high throughput production.
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| 63. |
- Bergqvist, J., et al.
(författare)
-
Sub-glass transition annealing enhances polymer solar cell performance
- 2014
-
Ingår i: Journal of Materials Chemistry A. - 2050-7488 .- 2050-7496. ; 2:17, s. 6146-6152
-
Tidskriftsartikel (refereegranskat)abstract
- Thermal annealing of non-crystalline polymer:fullerene blends typically results in a drastic decrease in solar cell performance. In particular aggressive annealing above the glass transition temperature results in a detrimental coarsening of the blend nanostructure. We demonstrate that mild annealing below the glass transition temperature is a viable avenue to control the nanostructure of a non-crystalline thiophene–quinoxaline copolymer:fullerene blend. Direct imaging methods indicate that coarsening of the blend nanostructure can be avoided. However, a combination of absorption and luminescence spectroscopy reveals that local changes in the polymer conformation as well as limited fullerene aggregation are permitted to occur. As a result, we are able to optimise the solar cell performance evenly across different positions of the coated area, which is a necessary criterion for large-scale, high throughput production.
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| 64. |
- Bergqvist, Jonas, et al.
(författare)
-
Uniaxial Anisotropy in PEDOT:PSS Electrodes Enhances the Photocurrent at Oblique Incidence in Organic Solar Cells
- 2018
-
Ingår i: ACS Photonics. - : AMER CHEMICAL SOC. - 2330-4022. ; 5:8, s. 3023-3030
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Tidskriftsartikel (refereegranskat)abstract
- PEDOT:PSS is a well studied organic conductor, commonly used as a transparent electrode material in printed organic devices such as organic solar cells. PEDOT:PSS thin films are known to be uniaxially anisotropic and exhibit a lower extinction coefficient and lower refractive index in the out of plane direction. To determine the maximum attainable photocurrent in thin film solar cells, the optical power dissipation can be calculated by the transfer matrix method. However, until now the anisotropic properties of PEDOT:PSS films have not been included in the model. In this work we have included an uniaxial anisotropic treatment of PEDOT:PSS films. We investigate reversed and semitransparent solar cells, with aluminum and PEDOT:PSS respectively as the second electrode and PEDOT:PSS as the top electrode, as compared to devices with isotropic PEDOT:PSS electrodes. For p-polarized light at large oblique incidence the inclusion of anisotropy shows a gain of over 7% for the maximum photocurrent in reversed solar cells. In semitransparent solar cells the photocurrent enhancement reaches 4-5% for p-polarized light. However, an enhancement of optical power dissipation and thus photocurrent generation of close to 40% is calculated for wavelengths close to the absorber bandgap. This work shows that for correct calculations of optical power dissipation in devices with PEDOT:PSS electrodes anisotropy should be included in the optical model. This will be especially important to determine the daily energy output of organic solar cells as their expected first markets are on building facades and indoor applications with larger fractions of diffuse light at large oblique incidence.
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| 65. |
- Bian, Qingzhen, et al.
(författare)
-
Reduced Nonradiative Voltage Loss in Terpolymer Solar Cells
- 2020
-
Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 11:10, s. 3796-3802
-
Tidskriftsartikel (refereegranskat)abstract
- The dissociation of hybrid local exciton and charge transfer excitons (LE-CT) in efficient bulk-heterojunction nonfullerene solar cells contributes to reduced nonradiative photovoltage loss, a mechanism that still remains unclear. Herein we studied the energetic and entropic contribution in the hybrid LE-CT exciton dissociation in devices based on a conjugated terpolymer. Compared with reference devices based on ternary blends, the terpolymer devices demonstrated a significant reduction in the nonradiative photovoltage loss, regardless of the acceptor molecule, be it fullerene or nonfullerene. Fourier transform photocurrent spectroscopy revealed a significant LE-CT character in the terpolymer-based solar cells. Temperature-dependent hole mobility and photovoltage confirm that entropic and energetic effects contribute to the efficient LE-CT dissociation. The energetic disorder value measured in the fullerene- or nonfullerene-based terpolymer devices suggested that this entropic contribution came from the terpolymer, a signature of higher disorder in copolymers with multiple aromatic groups. This gives new insight into the fundamental physics of efficient LE-CT exciton dissociation with smaller nonradiative recombination loss.
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| 66. |
- Bian, Qingzhen, 1988-, et al.
(författare)
-
Vibronic coherence contributes to photocurrent generation in organic semiconductor heterojunction diodes
- 2020
-
Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 11:1
-
Tidskriftsartikel (refereegranskat)abstract
- Charge separation dynamics after the absorption of a photon is a fundamental process relevant both for photosynthetic reaction centers and artificial solar conversion devices. It has been proposed that quantum coherence plays a role in the formation of charge carriers in organic photovoltaics, but experimental proofs have been lacking. Here we report experimental evidence of coherence in the charge separation process in organic donor/acceptor heterojunctions, in the form of low frequency oscillatory signature in the kinetics of the transient absorption and nonlinear two-dimensional photocurrent spectroscopy. The coherence plays a decisive role in the initial 200 femtoseconds as we observe distinct experimental signatures of coherent photocurrent generation. This coherent process breaks the energy barrier limitation for charge formation, thus competing with excitation energy transfer. The physics may inspire the design of new photovoltaic materials with high device performance, which explore the quantum effects in the next-generation optoelectronic applications.
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| 67. |
- Bjorstrom, Cecilia M., et al.
(författare)
-
Influence of solvents and substrates on the morphology and the performance of low-bandgap polyfluorene: PCBM photovoltaic devices - art. no. 61921X
- 2006
-
Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : International Society for Optical Engineering; 1999. - 0277-786X .- 1996-756X. ; 6192, s. X1921-X1921
-
Tidskriftsartikel (refereegranskat)abstract
- Spin-coated thin films of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] (APFO-3) blended with [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) are used as the active material in polymer photovoltaic cells. Such blends are known for their tendency to phase separate during film formation. Tuning the morphology of the blend in a controlled way is one possible road towards higher efficiency. We studied the effect of adding chlorobenzene to chloroform-based blend solutions before spin-coating on the conversion efficiency of APFO-3:PCBM photodiodes, and related that to the lateral and vertical morphology of thin films of the blend. The lateral morphology is imaged by atomic force microscopy (AFM) and the vertical compositional profile is obtained by dynamic secondary ion mass spectrometry (SIMS). The profiles reveal compositional variations consisting of multilayers of alternating polymer-rich and PCBM-rich domains in the blend film spin-coated from chloroform. The vertical compositional variations are caused by surface-directed spinodal waves and are frozen in during the rapid evaporation of a highly volatile solvent. With addition of the low-vapour pressure solvent chlorobenzene, a more homogeneous vertical composition is found. The conversion efficiency for solar cells of this blend was found to be optimal for chloroform: chlorobenzene mixtures with a volume-ratio of 80:1. We have also investigated the role of the substrate on the morphology. We found that blend films spin-coated from chloroform solutions on PEDOT:PSS-coated ITO show a similar compositional structure as the films on silicon, and that changing the substrate from silicon to gold only affects the vertical phase separation in a region close to the substrate interface.
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| 68. |
- Björk, Per, et al.
(författare)
-
Biomolecular nanowires decorated by organic electronic polymers
- 2010
-
Ingår i: JOURNAL OF MATERIALS CHEMISTRY. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 20:12, s. 2269-2276
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the shaping and forming of organic electronic polymers into designer nanostructures using biomacromolecules. In order to create nanowires, nanohelixes and assemblies of these, we coordinate semiconducting or metallic polymers to biomolecular polymers in the form of DNA and misfolded proteins. Optoelectronic and electrochemical devices utilizing these shaped materials are discussed.
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| 69. |
- Björk, Per, et al.
(författare)
-
Conjugated polythiophene probes target lysosome-related acidic vacuoles in cultured primary cells
- 2007
-
Ingår i: Molecular and Cellular Probes. - : Elsevier BV. - 0890-8508. ; 21:5-6, s. 329-337
-
Tidskriftsartikel (refereegranskat)abstract
- Conformation-sensitive optical probes for studying biological processes and structures are of great interest. The present work shows for the first time that conjugated polyelectrolyte (CPE) probes can be used for specific targeting of chromatin, nuclear and cytoplasmatic vesicles, and cytoskeletal components in a complex system of cultured cells. One of the probes could also be used for vital staining of live cells. When bound to different entities, the polythiophene derivative probes emitted light with different colors due to the unique spectral properties of these conformation sensitive probes. The physical pre-requisites for binding could also be exploited for characterization of the target. Unexpectedly, lysosome-related acidic vacuoles were targeted in cultured primary cells by both anionic, cationic, and zwitter-ionic polythiophene derivatives. Pre-treatment with Bafilomycin A1, a specific inhibitor of vacuolar-type H+-ATPase, caused redistribution of the staining. The targeting of lysosome-related acidic vesicles could not be demonstrated in transformed cells (melanoma, neuroblastoma, and prostate cancer cell lines), indicating a difference in the localization, structure, accessibility, or quantity of the target in cultured normal cells as compared with the malignant cell lines. The chemical nature of the conjugated polyelectrolyte complex in the cytoplasmatic vacuoles remains elusive.
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| 70. |
- Björk, Per, et al.
(författare)
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Dynamics of complex formation between biological and luminescent conjugated polyelectrolytes - a surface plasmon resonance study
- 2005
-
Ingår i: Biosensors and Bioelectronics. - : Elsevier BV. - 0956-5663. ; 20:9, s. 1764-1771
-
Tidskriftsartikel (refereegranskat)abstract
- A water-soluble polythiophene, POWT, with zwitterionic peptide like side chains possess good characteristics for biosensor applications. The zwitterionic side chains of the polymer can couple to biomolecules via electrostatic and hydrogen bonding. This creates possibilities to imprint biomolecules to spin-coated polymer films with maintained functionality, and use the resulting matrix as a biosensor. Polymer-biomolecular interaction studies done with surface plasmon resonance (SPR) reveal a well performing sensor matrix with high affinity for DNA hybridizations as well as for protein detection. The responses are distinct and very specific. A directional dependence of antibodies binding to POWT layer has also been observed. The polymer films have also been characterized by optical methods. Emission and absorption measurements in different buffer systems confirm that the polymer matrix can undergo structural and conformational changes on surfaces. The dielectric function in the interval 300–800 nm of POWT is reported, based on variable angle spectroscopic ellipsometry. This modeling reveals that a considerable amount of water is included in the material. The polymer layer possesses the characteristics needed for biochip applications and micro array techniques.
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