Plastic Solar Cells Based on Fluorenone-Containing Oligomers and Regioregular Alternate Copolymers (original) (raw)
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International Journal of Computational and Theoretical Chemistry
Organic photovoltaic performance has been investigated about the fluorination effects as one part on the optoelectronic properties. The quantum chemical accuracy of the optoelectronic and structural properties based on D-A (Donor-Acceptor) conjugated copolymers as PDTPQ X-type (Poly-dithieno-pyrrol-Quinoxaline) has been tediously exposed. The Donor-Acceptor in the copolymers was in our case constitutes to the Donor part in the photovoltaic device, while the Acceptor starting is the PC 60 BM in the same device, which composed the photovoltaic solar cells. The choice of the Donor part in the copolymers was obtained by their HOMO-LUMO bandgap and UV-visible absorption. The bandgap of the Donor part must be higher than that of the Acceptor part for an untroubled charges transfer from the Donor to the Acceptor according to the photovoltaic principle. The substitution of fluorine atoms (0F, 1F, 2F) on the quinoxaline constituents is an effective way to low the HOMO and LUMO energy levels of the alternating copolymers. This fluorine effect has been explored on the optoelectronic properties such as the HOMO-LUMO band gap E gap energy, the fill factor FF, the open circuit voltage V oc , the electron transfer energy ∆E et , the excitation energy ∆E ex , the absorption wave length λ and the oscillator strength OS. The equilibrium geometry at the ground state, the electronic structures as the frontier orbital isosurface have been obtained under the caster of the density functional theory (DFT) assist by the time-dependent density functional theory (TD-DFT) with M05 as exchange-correlation functional to come with 6-311G(d,p) basis set. Calculations were performed both in vaccuum and Chlorobenzene (CB) solvent with IEFPCM quantum model. All this has been done with the aim to enhance the energy gap, the V oc values and the fill factor FF, which exposed the nanomorphology as the topology of the solar cells photoactive layers. The results of this study show that these promote compounds systems as in the fluorination order are excellent candidates to build photovoltaic device in aim to enhance the open-circuit voltage for donor-acceptor heterojunctions used in organic solar cells.
Organic Electronics, 2017
Direct arylation polymerization (DAP) is emerging as a promising green, cheap, simple, and efficient environment friendly method for synthesizing conjugated polymers without involving any organometallic reagent. We report fluorene based novel cross-conjugated alternate and random copolymers for polymer solar cells (PSCs), which were synthesized by DAP and/or Yamamoto polymerization under appropriate reaction conditions to obtain high molecular weight. These cross-conjugated polymers possess absorption maxima in the range of 490e520 nm and have narrow band gap (1.7e2.05 eV) which is suitable for bulk heterojuntion (BHJ) type organic solar cells. Among the synthesized polymers, the highest number average molecular weight (M n) i.e. 43.1 kg mol À1 was obtained for polymer P2b (poly((9H-fluoren-9-ylidene)methylene)bis((2-ethylhexyl)sulfane)-alt-4,7-di(thiophen-2-yl)benzo[c] [1,2,5]thiadiazole)), and so good polymeric films were formed for P2b. Thus, BHJ films were prepared for P2b for device performance studies and the morphology of these films was studied by atomic force microscopy (AFM). Polymer P2b was blended with the fullerene derivative [6,6]-phenyl C 71 butyric acid methyl ester (PC 71 BM) in different ratios and under the illumination of solar simulator with Air Mass global (AM 1.5G) irradiated at 100 mW cm À2. Power conversion efficiency (PCE) of 1.4% has been achieved for BHJs in ratio of 1:2 of P2b: PC 71 BM in simply processed devices. This result indicates that crossconjugated polymers can be tapped as potential donors for BHJs as the PCE obtained is the highest among this type of cross-conjugated polymers.
New acceptor–donor–acceptor (A–D–A) type copolymers for efficient organic photovoltaic devices
Journal of Physics and Chemistry of Solids, 2015
Three new conjugated systems alternating acceptor-donor-acceptor (A-D-A) type copolymers have been investigated by means of Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) at the 6-31g (d) level of theory. 4,4 0-Dimethoxy-chalcone, also called the 1,3-bis(4-methoxyphenyl)prop-2en-1-one (BMP), has been used as a common acceptor moiety. It forced intra-molecular S⋯O interactions through alternating oligo-thiophene derivatives: 4-AlkylThiophenes (4-ATP), 4-AlkylBithiophenes (4-ABTP) and 4-Thienylene Vinylene (4-TEV) as donor moieties. The band gap, HOMO and LUMO electron distributions as well as optical properties were analyzed for each molecule. The fully optimized resulting copolymers showed low band gaps (2.2-2.8 eV) and deep HOMO energy levels ranging from À 4.66 to À 4.86 eV. A broad absorption [300-900 nm] covering the solar spectrum and absorption maxima ranges from 486 to 604 nm. In addition, organic photovoltaic cells (OPCs) based on alternating copolymers in bulk heterojunction (BHJ) composites with the 1-(3-methoxycarbonyl) propyl-1-phenyl-[6,6]-C 61 (PCBM), as an acceptor, have been optimized. Thus, the band gap decreased to 1.62 eV, the power conversion efficiencies (PCEs) were about 3-5% and the open circuit voltage V oc of the resulting molecules decreased from 1.50 to 1.27 eV.
Molecular design of D–A–D conjugated molecules based on fluorene for organic solar cells
Optical and Quantum Electronics, 2019
The aim of this work is to search for new molecules with a photovoltaic performance for use in the field of organic solar cells. To achieve this goal, starting from a series of D-AD bis-dipolar emissive oligoarylfluorenes and derivatives, the acceptor unit (A) is replaced by other different acceptors to improve their electronic optical and photovoltaic properties. The calculations were done using the B3LYP method with the base 6-31G(d,p) to optimize the geometry of the studied molecules and to determine the energies of HOMO, LUMO and band Gap. On the other hand, in order to study the electronic excitation spectra, the TD-B3LYP/6-31G (d,p) were used to calculate the absorption properties (λ max , OS). The results show that the designed molecules proposed here exhibit better performances including lower HOMO energy, a larger absorption range and better theoretical open circuit voltage (V OC). These compounds can be used as potential electron donors in organic solar cells Hetero-junction (BHJ), thanks to their better electronic and optical properties and good photovoltaic PV.
Journal of Polymer Science Part A: Polymer Chemistry, 2011
In this study, two low bandgap copolymers composed of fluorene (Fl), cyclopentadithiophene (CDT), and 4,7bis(2-thienyl)-2,1,3-benzothiadiazole (DBT) were synthesized, and their optical, electrochemical, and photovoltaic (PV) characteristics were investigated for applications in PV devices. The feed ratio of the Fl and CDT moieties was modulated to tune the electronic structures and resulting optical properties of the polymers. In the copolymeric structures, the Fl-CDT unit absorbs the short-wavelength UV/vis regions, and the CDT-DBT (or Fl-DBT) unit with strong intramolecular charge transfer characteristics covers the long-wavelength visible regions. P1 exhibited a wide UV absorption spectrum covering the UV and entire visible region in the range of 300-800 nm, and P2 showed absorption covering from 300 to 700 nm. UV/vis and electrochemical studies confirmed the desirable highest occupied molecular orbital/ lowest unoccupied molecular orbital levels of the copolymers with bandgaps of 1.62-1.86 eV, enabling efficient electron transfer and a high open-circuit voltage when blending them with fullerene derivatives. When the polymers were blended with [6,6]phenyl-C 61-butyric acid methyl ester, P1 exhibited the best device performance with an open-circuit voltage of 0.66 V, short-circuit current of 4.92 mA cm À2 , and power conversion efficiency of 1.13% under Air Mass 1.5 Global (AM 1.5G, 100 mW cm À2) illumination. V
Alternating Copolymers and Alternative Device Geometries for Organic Photovoltaics
AMBIO, 2012
The efficiency of conversion of light to electrical energy with the help of conjugated polymers and molecules is rapidly improving. The optical absorption properties of these materials can be designed, and implemented via molecular engineering. Full coverage of the solar spectrum is thus feasible. Narrow absorption spectra allow construction of tandem solar cells. The poor transport properties of these materials require thin devices, which limits optical absorption. Alternative device geometries for these flexible materials compensate for the optical absorption by light trapping, and allow tandem cells.
Http Www Theses Fr, 2012
Organic photovoltaic (OPV) cells have been a subject of increasing interest during the last decade as they are promising candidates for low cost renewable energy production. In order to obtain reasonably high performance organic solar cells, development of efficient light absorbing materials are of primary focus in the OPV field. In this context, the present work is focused on the design and development of new electron donor materials (oligomers and polymers) as light absorbing materials based on "Donor-Acceptor" approach alternating electron donating group and electron withdrawing group. Three main families of electron donating group are studied: oligothiophenes, fluorene and indacenodithiophene. Fluorenone unit is the principal electron withdrawing group studied and a direct comparison with the system based on benzothiadiazole unit as electron withdrawing unit is also provided. Three main synthetic methods were employed: oxidative polymerization mediated by Iron (III) chloride and Palladium cross-coupling reactions according to Suzuki coupling or Stille coupling conditions. Spectroscopic studies on absorption and photoluminescence have demonstrated the presence of characteristic charge transfer complex in all the studied D-A oligomers and polymers allowing the extension of the absorption spectrum. The D-A oligomers and polymers have shown an overall low optical band gap of 1.6-2 eV with absorption spectra up to 600 to 800 nm. The nature of the charge transfer complex transitions bands were found to be depending on the strength of the electron donating unit and the electron withdrawing unit. Furthermore molecular packing in solution and in solid state has also demonstrated to contribute to extension of absorption spectrum. The HOMO and LUMO energy levels of the oligomers and polymers were determined by electrochemical measurements. Fluorene-based polymers have shown low lying HOMO energy levels, and these polymers demonstrate high open circuit voltage (Voc) in photovoltaic cell when combined with fullerenes derivatives PCBM with Voc values close to 0.9 V. The oligomers and polymers tested in photovoltaic devices have shown promising results with the highest power conversion efficiency obtained of 2.1 % when combined with fullerenes PCBMC70. These results were obtained after only limited numbers of device optimizations such as the active materials ratios and thermal annealing. Therefore further optimization of devices may exhibit higher power conversion efficiencies. Résumé Les cellules photovoltaïques organiques ont fait l'objet d'un intérêt croissant au cours de ces dernières décennies car elles offrent un grand potentiel pour une production d'énergie renouvelable à faible coût. Afin d'obtenir des cellules solaires organiques à haut rendement de conversion d'énergie, beaucoup de recherches se focalisent sur les matériaux ayant des capacités à absorber la lumière efficacement. Dans ce contexte, le présent travail se concentre sur la conception et le développement de nouveaux matériaux donneurs d'électrons (oligomères et polymères) comme matériaux absorbant de la lumière basée sur l'approche « Donneur-Accepteur » alternant des segments riches en électron (donneur d'électron) et des unités pauvres en électron (accepteur d'électron). Trois séries d'unités riches en électron ont été étudiées: oligothiophènes, fluorène et indacenodithiophene. L'unité fluorénone est la principale unité « accepteur d'électron » étudiée. Une comparaison directe avec le système basé sur l'unité benzothiadiazole comme accepteur d'électron est également rapportée. Trois méthodes principales de synthèse ont été utilisées: polymérisation oxydante par le chlorure de fer (III), et les couplages croisés au palladium de type Suzuki ou de Stille. Les études spectroscopique UV-Visible en absorption et en photoluminescence sur ces oligomères et polymères ont démontré la présence de complexes à transfert de charges permettant d'élargir le spectre d'absorption. Les oligomères et les polymères possèdent des faibles largeurs de bande interdite de 1,6 eV à 2 eV. Les systèmes ayant des unités fluorénones présentent des spectres d'absorption étendus allant jusqu'à 600-700 nm, tandis que les systèmes ayant des unités benzothiadiazoles présentent des spectres d'absorption allant jusqu'à 700-800 nm. La nature des bandes de complexes à transfert de charge se révèle d'être dépendant de la force de respective des unités « donneur d'électrons » et des unités « accepteur d'électrons ». Les niveaux d'énergies HOMO et LUMO des oligomères et les polymères sont déterminés par des mesures électrochimiques. Les polymères à base de fluorène possèdent des niveaux d'énergie HOMO les plus bas. Ces polymères testés en mélange avec les fullerenes PCBM en cellules photovoltaïques ont démontré des valeurs élevées de tension en circuit ouvert (Voc) proche de 0,9 V. Tous les oligomères et les polymères ont été testés dans des dispositifs photovoltaïques et ont montré des résultats encourageants avec des rendements de conversion allant jusqu'à 2,1 %. Ce sont des premièrs résultats obtenus après seulement quelques optimisations (ratios oligomères ou polymères : fullerènes et recuit thermique). Ce travail prometteur permet ainsi d'envisager des résultats plus élevés dans le futur.