| 1. |
- Bolognesi, Margherita, et al.
(författare)
-
2D π-conjugated benzo[1,2-b:4,5-b']dithiophene- and quinoxaline-based copolymers for photovoltaic applications
- 2013
-
Ingår i: RSC Advances. - 2046-2069. ; 3:46, s. 24543-24552
-
Tidskriftsartikel (refereegranskat)abstract
- Two medium gap semiconducting polymers, P(1)-Q-BDT-4TR and P(2)-FQ-BDT-4TR, based on alternate units of alkyl-dithiophene substituted benzodithiophene (BDT) and quinoxaline units (without or with fluorine substitution), are synthesized and fully characterized. The polymers exhibit optical and electrical properties favorable for being employed as donors in BHJ OPV devices, such as: absorption spectra extending up to around 720 nm for a high solar spectrum coverage, deep lying HOMO energy levels for a high device open circuit voltage and LUMO energy levels higher than those of PC61BM and PC71BM for an efficient exciton dissociation. In particular, the presence of alkyl-dithiophene side chains allows us to obtain a high 2D π-conjugation which promotes red shifted absorption profiles, low HOMO energy levels (
|
|
| 2. |
- Gedefaw, Desta Antenehe, 1971, et al.
(författare)
-
Synthesis and characterization of benzodithiophene and benzotriazole-based polymers for photovoltaic applications
- 2016
-
Ingår i: Beilstein Journal of Organic Chemistry. - : Beilstein Institut. - 1860-5397. ; 12, s. 1629-1637
-
Tidskriftsartikel (refereegranskat)abstract
- Two high bandgap benzodithiophene-benzotriazole-based polymers were synthesized via palladium-catalysed Stille coupling reaction. In order to compare the effect of the side chains on the opto-electronic and photovoltaic properties of the resulting polymers, the benzodithiophene monomers were substituted with either octylthienyl (PTzBDT-1) or dihexylthienyl (PTzBDT-2) as side groups, while the benzotriazole unit was maintained unaltered. The optical characterization, both in solution and thin-film, indicated that PTzBDT-1 has a red-shifted optical absorption compared to PTzBDT-2, likely due to a more planar conformation of the polymer backbone promoted by the lower content of alkyl side chains. The different aggregation in the solid state also affects the energetic properties of the polymers, resulting in a lower highest occupied molecular orbital (HOMO) for PTzBDT-1 with respect to PTzBDT-2. However, an unexpected behaviour is observed when the two polymers are used as a donor material, in combination with PC61BM as acceptor, in bulk heterojunction solar cells. Even though PTzBDT-1 showed favourable optical and electrochemical properties, the devices based on this polymer present a power conversion efficiency of 3.3%, considerably lower than the efficiency of 4.7% obtained for the analogous solar cells based on PTzBDT-2. The lower performance is presumably attributed to the limited solubility of the PTzBDT-1 in organic solvents resulting in enhanced aggregation and poor intermixing with the acceptor material in the active layer.
|
|
| 3. |
- George, Zandra, 1985, et al.
(författare)
-
Improved performance and life time of inverted organic photovoltaics by using polymer interfacial materials
- 2015
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248. ; 133, s. 99-104
-
Tidskriftsartikel (refereegranskat)abstract
- A previously published fluorene based interlayer polymer is here compared to three similar polymers where the fluorene monomer has been exchanged with monomers that have been reported to have a higher photo-chemical stability. The polymer interlayers have been studied in terms of their influence on device performance and stability on inverted devices with an active layer of P3HT:PC61BM. By acting as a hole-blocking layer the polymers are able to increase the efficiency of the devices with similar to 50% compared to devices with an ITO cathode. In addition, the polymers also improve the photo-stability of the devices, mainly as an effect of a reduced decrease in open-circuit voltage and fill factor. This indicates that solution processable polymer interlayers could be a way towards both higher efficiency and improved stability of inverted organic solar cells.
|
|
| 4. |
- Hedström, Svante, et al.
(författare)
-
Light-harvesting capabilities of low band gap donor-acceptor polymers
- 2014
-
Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 16:45, s. 24853-24865
-
Tidskriftsartikel (refereegranskat)abstract
- A series of nine donor-acceptor polymers, including three new and six polymers from previous work, have been investigated experimentally and theoretically. The investigation focuses on narrow band gaps and strong absorptions of the polymers, where experimentally determined first peak absorption energies range from 1.8 to 2.3 eV, and peak absorption coefficients vary between 19-67 L g(-1) cm(-1). An overall assessment of each polymer's light-harvesting capability is made, and related to the chemical structure. Oligomer calculations using density functional theory are extrapolated to obtain size-converged polymer properties, and found to reproduce the experimental absorption trends well. Accurate theoretical predictions of absorption energies to within 0.06 eV of experiments, and absorption strength to within 12%, are obtained through the introduction of an empirical correction scheme. The computational and experimental results provide insight for the design of polymers with efficient absorption, concerning the intrinsic properties of the constituent units and the use of bulky side-groups.
|
|
| 5. |
- Hedström, Svante, et al.
(författare)
-
Temperature-Dependent Optical Properties of Flexible Donor - Acceptor Polymers
- 2015
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:12, s. 6453-6463
-
Tidskriftsartikel (refereegranskat)abstract
- Optical properties of five donor acceptor polymers of interest for light-harvesting in organic photovoltaic devices have been studied experimentally and computationally. Experimentally recorded absorption spectra in solution of the five polymers are shown to be significantly temperature-dependent. The polymers were subjected to a first-principles computational treatment using density functional theory optimizations and excitation calculations. For two of the polymers, APFO-3 and PTI-1, a methodology that accounts for a thermally induced distribution of conformations based on Boltzmann statistics is applied to produce size- and temperature-converged optical results. This provides a deeper understanding of the temperature dependence of optical properties and improves the computational predictions of absorption wavelength and intensity at experimentally accessible temperatures, as compared to results from traditional quantum chemical calculations based on optimized polymers. Together, the combined experimental and computational temperature studies elucidate and quantify the significant influence of structural flexibility on the optical absorption properties of typical donor acceptor polymers.
|
|
| 6. |
- Hellström, Stefan, 1978, et al.
(författare)
-
Blue-to-transmissive electrochromic switching of solution processable donor-acceptor polymers
- 2011
-
Ingår i: Organic Electronics: physics, materials, applications. - : Elsevier BV. - 1566-1199. ; 12:8, s. 1406-1413
-
Tidskriftsartikel (refereegranskat)abstract
- The electrochromic performance of poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diylalt-thiophene-2,5-diy l] (TQ1), switching from an intense blue color to a transmissive yellow-brown oxidized state, are presented. Additionally, two new polymers, based on the same polymeric backbone but with oligoethylene oxide (TQ2) and ethylhexyloxy (TQ3) side chains, were prepared to compare the structure-property relationships. TQ1 has the highest optical contrast, with a transmittance change of 50%, recorded by spectroelectrochemistry at the low-energy absorption maximum (623 nm). The high optical contrast, facile synthetic preparation, and processability through good solubility in organic solvents make TQ1 an interesting polymer for implementation in non-emissive electrochromic devices. Response times were improved by the introduction of ethylhexyloxy side chains (TQ3), where 92% of the transmittance modulation was maintained at switching times of 0.5 s. The influence of film thickness on optical contrast was also investigated, where the highest optical contrast for TQ1 was obtained for films having reduced absorption of 0.84 a.u. at the low-energy absorption maximum. All three polymers show decent electrochemical stability over 200 full switches.
|
|
| 7. |
- Henriksson, Patrik, 1983, et al.
(författare)
-
Stability study of quinoxaline and pyrido pyrazine based co-polymers for solar cell applications
- 2014
-
Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 130, s. 138-143
-
Tidskriftsartikel (refereegranskat)abstract
- We present two co-polymer families; one based on a thiophene-quinoxaline unit and one on a thiophene-pyrido pyrazine unit. Co-polymerization of these monomers with thiophene-hexylthiophene was performed to create polymers with an optical absorption that fully covers the visible part of the solar spectrum with the aim to enhance the solar cell performances of these polymers. We have also studied how increasing the fraction of thiophene-hexylthiophene affects the photo-oxidative stability of these polymers. Thiophene-pyrido pyrazine solar cells displayed increased device efficiency upon addition of the thiophene-hexylthiophene and, in addition, the stability is retained upon inclusion of these units. In contrast, we found that for the thiophene-quinoxaline based co-polymer, both device efficiency and stability decreased with increasing thiophene-hexylthiophene fraction. Moreover, our results indicate that the photo-oxidative stability of the thiophene-quinoxaline co-polymer is independent of the polymer molecular weight as well as of the film thickness.
|
|
| 8. |
- Lindqvist, Camilla, 1985, et al.
(författare)
-
Fullerene Nucleating Agents: A Route Towards Thermally Stable Photovoltaic Blends
- 2014
-
Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6840 .- 1614-6832. ; 4:9, s. 1301437-
-
Tidskriftsartikel (refereegranskat)abstract
- The bulk-heterojunction nanostructure of non-crystalline polymer: fullerene blends has the tendency to rapidly coarsen when heated above its glass transition temperature, which represents an important degradation mechanism. We demonstrate that fullerene nucleating agents can be used to thermally arrest the nanostructure of photovoltaic blends that comprise a non-crystalline thiophene-quinoxaline copolymer and the widely used fullerene derivative [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM). To this end, C-60 fullerene is employed to efficiently nucleate PCBM crystallization. Sub-micrometer-sized fullerene crystals are formed when as little as 2 wt% C-60 with respect to PCBM is added to the blend. These reach an average size of only 200 nanometers upon introduction of more than 8 wt% C-60. Solar cells based on C-60-nucleated blends indicate significantly improved thermal stability of the bulk-heterojunction nanostructure even after annealing at an elevated temperature of 130 degrees C, which lies above the glass transition temperature of the blend. Moreover, we find that various other compounds, including C-70 fullerene, single-walled carbon nanotubes, and sodium benzoate, as well as a number of commercial nucleating agents-commonly used to clarify isotactic polypropylene-permit to control crystallization of the fullerene phase.
|
|
| 9. |
- Ma, Zaifei, et al.
(författare)
-
Synthesis and characterization of benzodithiophene-isoindigo polymers for solar cells
- 2012
-
Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 1364-5501 .- 0959-9428. ; 22:5, s. 2306-2314
-
Tidskriftsartikel (refereegranskat)abstract
- Three new alternating polymers with the electron-deficient isoindigo group as the acceptor unit and benzo[1,2-b:4,5-b'] dithiophene (BDT) or BDT flanked by thiophenes (or octylthiophenes) as the donor unit were designed and synthesized. All the polymers have good thermal stability, solubility and broad absorption spectra. Their photophysical, electrochemical and photovoltaic (PV) properties were investigated. To understand their different PV performance in the resulting polymer solar cells (PSCs), the morphology of their blends with fullerene derivatives was investigated by atomic force microscopy, and the molecular geometries as well as the molecular frontier orbitals were simulated by density functional theory calculations (Gaussian 09). The polymer PBDT-TIT, with BDT flanked by thiophenes as the donor unit and isoindigo as the acceptor unit, exhibits quite planar backbones and its blend with fullerene derivatives shows optimal morphology. As a result, the PSCs based on PBDT-TIT with a conventional device configuration of ITO/PEDOT: PSS/PBDT-TIT: PC(61)BM/LiF/Al showed a power conversion efficiency of 4.22%, with a short-circuit current density of 7.87 mA cm(-2), an open-circuit voltage of 0.79 V and a fill factor of 0.68 under the AM 1.5G illumination with an intensity of 100 mW cm(-2) from a solar simulator.
|
|
| 10. |
- Tessarolo, Marta, et al.
(författare)
-
Structural tuning of quinoxaline-benzodithiophene copolymers via alkyl side chain manipulation: synthesis, characterization and photovoltaic properties
- 2014
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 2:29, s. 11162-11170
-
Tidskriftsartikel (refereegranskat)abstract
- We report here the synthesis and characterization of two novel semiconducting quinoxaline (FQ)-benzodithiophene (BDT) based copolymers, PFQBDT-TR1 and PFQBDT-T2R(2), in which the BDT unit is substituted with either 2-octylthienyl (-TR1) or 2,3-dihexylthienyl (-T2R(2)), respectively, as side groups. The effect of the alkyl side chain(s), linked to the thienyl side groups, on the optical, electronic and morphological properties of the resulting polymers is investigated and correlated with the photovoltaic performance. Solution-processed BHJ solar cells, using these copolymers as electron donor materials and PC61BM (or PC71BM) as an electron acceptor counterpart, are prepared by a blade-coating technique under ambient conditions. As a result, power conversion efficiencies (PCEs) of similar to 5.7% and similar to 3.4% have been achieved for PFQBDT-TR1 and PFQBDT-T2R(2) based devices, respectively, highlighting the crucial role of the alkyl portion of the pi-conjugated side segment in the optoelectronic properties of this class of copolymers.
|
|
