Organic and Hybrid Solar Cells Based on Well-Defined Organic Semiconductors and Morphologies (original) (raw)
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Chemistry of Materials, 2009
The solid state organization of molecules is an important factor in determining the performance of organic electronic devices. In bulk heterojunction (BHJ) solar cells, the arrangement of electron donor and acceptor materials into distinct crystalline phases of ideal size and distribution can lead to better power conversion efficiencies. The use of fluorenyl hexa-peri-hexabenzocoronene (FHBC) 2 in this study has highlighted the importance of molecular organization to device performance. FHBC compounds 6, 8, and 10, functionalized with a series of thiophene dendrons, were synthesized using Suzuki-Miyaura coupling in high yields. In UV-vis and 1 H NMR spectroscopic studies, all FHBC derivatives showed self-association in solution. Hexagonal packing of columnar structures was observed for solid state samples of FHBC 2 and 8 in two-dimensional wide-angle X-ray scattering experiments. In thin film X-ray experiments, ordered structures were observed in blends of FHBC 2 and fullerene acceptor materials indicating that there is phase separation between the donor and acceptor materials and that the self-organization of the FHBC material is unaffected. While the large thiophene dendritic substituent attached to compound 10 broadened its UV-vis absorption profile, the solid state morphology is altered by the bulky thiophene dendrons. These molecular structure variations are reflected in the performance characteristics of BHJ solar cell devices fabricated using these FHBC compounds as electron donor materials. Power conversion efficiency of 2.5% was achieved for a device containing compound 10 with [6,6]-phenyl-C71-butyric acid methyl ester (PC 71 BM) as the acceptor material. This compares favorably with devices fabricated with pure dendritic thiophene materials and illustrates the positive effect of molecular self-organization on device performance. (1) Scharber, M. C.; M€ uhlbacher, D.; Koppe, M.; Denk, P.; Waldauf, C.; Heeger, A. J.; Brabec, C. J. Adv. Mater. 2006, 18, 789-794. (2) Halls, J. J. M.; Pichler, K.; Friend, R. H.; Moratti, S. C.; Holmes, A. B.
Bulk heterojunction organic photovoltaic devices based on phenyl-cored thiophene dendrimers
Applied Physics Letters, 2006
Bulk heterojunction organic photovoltaic devices have been fabricated by blending phenyl-cored thiophene dendrimers with a fullerene derivative. A power conversion efficiency of 1.3% under simulated AM1.5 illumination is obtained for a four-arm dendrimer, despite its large optical band gap of 2.1 eV. The devices exhibit an increase in short-circuit current and power conversion efficiency as the length of the arm is increased. The fill factors of the devices studied are characteristically low, which is attributed to overly uniform mixing of the blend.
Thiophene dendrimer-based low donor content solar cells
Low donor content solar cells containing polymeric and non-polymeric donors blended with fullerenes have been reported to give rise to efficient devices. In this letter, we report that a dendrimeric donor can also be used in solution-processed low donor content devices when blended with a fullerene. A third generation dendrimer containing 42 thiophene units (42T) was found to give power conversion efficiencies of up to 3.5% when blended with PC70BM in optimized devices. The best efficiency was measured with 10 mole percent (mol. %) of 42T in PC70BM and X-ray reflectometry showed that the blends were uniform. Importantly, while 42T comprised 10 mol. % of the film, it made up 31% of the film by volume. Finally, it was found that solvent annealing was required to achieve the largest open circuit voltage and highest device efficiencies.
2017
In this study, we report a theoretical investigations on the structural, optoelectronic and photovoltaic properties of a series of conjugated organic molecules containing thieno[2,3-b]thiophene, with different substituents. The DFT calculations were performed by using the quantum chemical methods using B3LYP [1] level with 6-31G(d) [2] basis set for all atoms. All calculations were realized by Gaussian 09 [3] program supported by GaussView 5.0.8 interface. Moreover, the optoelectronic properties (HOMO, LUMO, Egap…) were determined from the fully optimized structures. The absorption properties (λmax, Etr, OS) of these molecules are obtained by TD-B3LYP/6-31G(d) method [4]. The studied oligomers can be subdivided in three categories; the first one constitutes by synthetized oligomers [5] but is characterized with the highest energy band values. Thanks to the effect of structural modifications in there chemical structures in the second and the third categories, the energy gap values ha...
Applied Physics Letters, 2008
Poly͑2,5-bis͑3-tetradecyllthiophen-2-yl͒thieno͓3,2-b͔thiophene͒ ͑pBTTT͒ has caused recent excitement in the organic electronics community because of its high reported hole mobility ͑0.6 cm 2 V −1 s −1 ͒ that was measured in field effect transistors and its ability to form large crystals. In this letter, we investigate the potential of pBTTT as light absorber and hole transporter in a bulk heterojunction solar cell. We find that the highest efficiency of 2.3% is achieved by using a 1:4 blend of pBTTT and͓6,6͔-phenyl C 61-butyric acid methyl ester. The hole mobility as measured by space charge limited current modeling was found to be 3.8ϫ 10 −4 cm 2 V −1 s −1 in this blend.
High open-circuit voltage bulk-heterojunction solar cells by using new dendritic acceptor material
Light harvesting solar cells and energy transfer are currently of great challenges for the 21st century in the field of solar cells energy. Academic and industrial scientists are searching for a detailed understanding of light harvesting and find tools to control the electron transfer between donor and acceptor molecules. Due to their electronic properties and the ability to tune their absorption ranges, conjugated dendrimers combined with polymers are used extensively in the formation of the active layer (donor- acceptor) in organic photovoltaic [1]. Dendrimers and hyperbranched polymers are considered to be the leading materials used in the application of organic solar cells. They are low viscosity with high molecular weights, good solubility and mutifunctionality. Dendrimers are perfect monodisperse macromelcular (tree-like structures) with high branched three-dimensional structures: core, branches, and end groups [1, 2]. Organic bulk-heterojunction structure (OBHJ) consist of do...
Journal of Photochemistry and Photobiology A: Chemistry, 2013
After the discovery of photoinduced charge transfer in conjugated polymers, organic photovoltaic solar cells have been extensively studied due to many advantages that include flexibility and low-cost. In this context, we have synthesized a new class of conjugated polymer, poly(2-(4-{1-cyano-2-[5-(3-thiophen-2-yl-benzo[c]thiophen-1-yl)-thiophen-2-yl]-vinyl}-2,5bis-hexyloxy-phenyl)-but-2-enenitrile) (CN-PTBTBPB) for the fabrication of low cost organic solar cells. The electron donor properties of CN-PTBTBPB polymer was incorporated by means of facile Knoevenagel condensation process followed by a chemical oxidative polymerization method using oligo-5-(1-benzo[c]thiophen-3-yl)thiophene-2-carboxaldehyde with 1,4-bis(cyanomethyl) benzene linkages. The polymer was characterized by 1 H NMR and GPC techniques. The electronic and structural properties of the polymer were evaluated by UV-vis spectroscopy, fluorescence spectroscopy, and thermo gravimetric analysis. In order to establish the energy diagram of the prepared polymer, the energy gap between HOMO-LUMO was evaluated using electrochemical measurements and Density Functional Theory (DFT). The resulting CN-PTBTBPB polymer was experimentally found to possess low-lying HOMO (about −5.84 eV) and high-lying LUMO (about −3.87 eV) energy levels. This polymer exhibited a relatively wide optical band gap of ∼1.95 eV in the solid state. Using this polymer, organic photovoltaic cells were fabricated in open air of type ITO/PEDOT:PSS/CN-PTBTBPB:PCBM/Al showed promising photovoltaic properties.
Bulk heterojunction organic solar cells based on soluble poly(thienylene vinylene) derivatives
Organic electronics, 2008
We report on the comparison of photophysical and photovoltaic properties of three different soluble alkyl derivatives of the low bandgap poly(2,5-thienylene vinylene) (PTV), synthesized using the dithiocarbamate precursor route. The solubility of the precursor material in dichlorobenzene is enhanced by the addition of hexyl, dihexyl and dodecyl sidegroups to the polymer chain. The materials were characterized in solid state by means of absorption, ellipsometry and atomic force microscopy of films made from both the pristine alkyl-PTVs and alkyl-PTVs:([6,6]-phenyl C 61 -butyric acid methyl ester) (PCBM) mixtures in a 1:1 ratio. The materials showed an optical bandgap below 1.7 eV, derived from the absorption spectrum of the polymers. Field-effect transistors made of these materials showed hole mobilities in the range of 10 À7 to 10 À6 cm 2 /Vs. Bulk heterojunction solar cells made with the polymer:PCBM blend reached efficiencies above 0.6%.
Solar Energy Materials and Solar Cells, 2006
Photophysical studies and photovoltaic devices on a low bandgap, high-charge carrier mobility poly(thienylene vinylene) (PTV), prepared from a soluble precursor polymer synthesised via the ''dithiocarbamate route'', are reported. In composites with an electron acceptor ([6,6]-phenyl C 61 -butyric acid methyl ester (PCBM), a soluble fullerene derivative), photoinduced absorption characteristic for charged excitations together with photoluminescence quenching are observed indicating photoinduced electron transfer. The ''bulk heterojunction'' photovoltaic devices using PTV and PCBM composites show short-circuit currents up to 4 mA/cm 2 under AM 1.5 white-light illumination. The photocurrent spectrum of the photovoltaic device shows an onset about 1.65 eV (750 nm), which corresponds to the absorption spectrum of the polymer. r