Dimethyl-2H-benzimidazole based small molecules as donor materials for organic photovoltaics (original) (raw)
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Chemistry of Materials, 2011
A new series of electron-deficient molecules based on a central benzothiadiazole moiety flanked with vinylimides has been synthesized via Heck chemistry and used in solution-processed organic photovoltaics (OPV). Two new compounds, 4,7bis(4-(N-hexyl-phthalimide)vinyl)benzo[c]1,2,5-thiadiazole (PI-BT) and 4,7-bis(4-(N-hexylnaphthalimide)vinyl)benzo[c]1,2,5-thiadiazole (NI-BT), show significantly different behaviors in bulk heterojunction (BHJ) solar cells using poly(3-hexylthiophene) (P3HT) as the electron donor. Two-dimensional grazing incidence X-ray scattering (2D GIXS) experiments demonstrate that PI-BT shows significant crystallization in spin-coated thin films, whereas NI-BT does not. Density functional theory (DFT) calculations predict that while PI-BT maintains a planar structure in the ground state, steric interactions cause a twist in the NI-BT molecule, likely preventing significant crystallization. In BHJ solar cells with P3HT as donor, PI-BT devices achieved a large open-circuit voltage of 0.96 V and a maximum device powerconversion efficiency of 2.54%, whereas NI-BT containing devices only achieved 0.1% power-conversion efficiency.
Synthetic Metals, 2013
Low-band-gap organic semiconducting polymers comprising two dialkoxy-substituted Benzoselenadiazole derivatives and two BDT derivatives as the electron acceptors and donors, respectively, were synthesized via Stille coupling for application as a donor material in organic photovoltaic cells. These polymers are soluble in common organic solvents, and can be spin-cast to form smooth, uniform thin films. The polymers were thermally stable, i.e., lost < 5% of their weight upon
Organic Electronics, 2015
Two benzothiazole (BT) based donor-acceptor-p-acceptor (D-A-p-A) molecular system denoted as BT3 and BT4 have been designed, synthesized and their optical and electrochemical properties were investigated. The BT4 show wider absorption profile and lower bandgap as compared to BT3 due to the strong electron withdrawing ability of dicyanoquinodimethane (DCNQ) as compared to tetracyanobutadiene (TCBD). The solution processed bulk heterojunction solar cells were fabricated using BT3 and BT4 as electron donor and PC 71 BM as electron acceptor. The organic solar cells optimized dichloromethane (DCM) processed BT3:PC 71 BM (1:1) and BT4:PC 71 BM (1:1) showed PCE of 2.56% and 3.68%, respectively. The higher PCE of BT4:PC 71 BM is related to the wider absorption of the blend and better ordered domain sizes in the blend as compared to BT3:PC 71 BM. The devices processed with 1,8-diiodoctane (DIO) additives showed PCE of 3.77% and 5.27%, for BT3:PC 71 BM and BT4:PC 71 BM blends, respectively.
Concept of Organic Photovoltaics: Operational Principles and Materials
Acta Electrotechnica et Informatica, 2013
Organic molecules possessing a π-conjugated (hetero)aromatic backbone are capable of transporting charge and interact efficiently with light. Therefore, these systems can act as semiconductors in opto-electronic devices similar to inorganic materials. However, organic chemistry offers tools for tailoring materials' functional properties via modifications of the molecular units, opening new possibilities for inexpensive device manufacturing. In this presentation, we discuss exploitation of such organic molecular systems in photovoltaics; the operation, advantages, and limitations of molecular donor-acceptor heterojunction structures.
Simple and Versatile Molecular Donors for Organic Photovoltaics Prepared by Metal-Free Synthesis
Chemistry - A European Journal, 2014
Donor-acceptor molecules (D-p-A) built by connecting a diphenylhydrazone block to a dicyanovinyl acceptor group via various thiophene-based p-conjugating spacers (1-5) were synthesized from mono-or dialdehydes by a simple metal-free procedure. Cyclic voltammetry and UV/ Vis absorption spectroscopy show that the extension and/or increase of the donor strength of the spacer produces a decrease of the HOMO and LUMO energy level, a red shift of the absorption spectrum and an increase of the molecular absorption coefficient. Compared to solutions, the optical spectra of spin-cast thin films of compounds 1-3 show a broadening and red shift of the absorption bands, consis-tent with the formation of J-aggregates. In contrast the blue shift observed for the EDOT-containing compounds 4 and 5 suggests the presence of H-aggregates. Solution-cast and vacuum-deposited films of donors 1-5 were evaluated in solar cells with fullerene C 60 as acceptor. A power-conversion efficiency among the highest reported for bilayer devices of basic configuration was obtained with compound 2. On the other hand, the results obtained with 4 and 5 suggest that the presence of EDOT in the structure can have deleterious effects on the organization and performances of the donor material.
Dicyanoquinodimethane-substituted benzothiadiazole for efficient small-molecule solar cells
Physical chemistry chemical physics : PCCP, 2016
Two unsymmetrical donor-acceptor-acceptor-π-acceptor type benzothiadiazoles (BTD3 and BTD4) functionalized with tetracyanobutadiene (TCBD) and dicyanoquinodimethane (DCNQ) modules, showing strong absorption in the visible region are reported. The bulk heterojunction solar cells based on BTD4:PC71BM and BTD3:PC71BM based active layers processed with chloroform (CF), thermal annealing and subsequent solvent vapor annealing, i.e. two step annealing (TSA), exhibited PCEs of up to 6.02% and 5.36%, respectively, which is significantly higher than those of the corresponding devices based on the as-cast blend active layer. This enhancement is related to the improvement in exciton dissociation efficiency and more balanced charge transport in the devices based on the active layer processed with TSA treatment.
Synthetic Metals, 2011
New semiconducting polymer with alkoxy substituted terthiophene, as the electron rich unit, and 2,2-(1,5-pentamethylene)-2H-benzimidazole (PMBI), as the electron deficient unit, was synthesized using Stille polymerization. The advantage of PMBI is higher solubility of the polymer while keeping the coplanarity of the backbone as compared to the benzothiadiazole moiety of PCDTBT. In PMBI, the sulfur at 2-position of BT unit was replaced with the carbon of cyclohexane to make a highly soluble electron deficient moiety while keeping the 1,2-quinoid form of BT unit. The polymer, PTBHOTPMBI, exhibits more red shifted absorption peak as compared to the polymers with benzothiadiazole unit. The PTBHOTPMBI thin film shows two broad absorption bands with peaks at 475 and 755 nm and an absorption onset at 943 nm, corresponding to a band gap of 1.32 eV. The device of PTBHOTPMBI with PC 71 BM showed an open-circuit voltage (V OC ) of 0.25 V, a short-circuit current density (J SC ) of 2.30 mA/cm 2 , and a fill factor (FF) of 0.30, giving a power conversion efficiency of 0.17%.
RSC Advances, 2014
Two new low band gap D–A structured conjugated polymers, PBDTTBI and PBDTBBT, based on 2-(4- (trifluoromethyl)phenyl)-1H-benzo[d]imidazole and benzo[1,2-c;4,5-c0]bis[1,2,5]thiadiazole acceptor units with benzo[1,2-b;3,4-b0]dithiophene as a donor unit have been designed and synthesized via a Stille coupling reaction. The incorporation of the benzo[1,2-c;4,5-c0]bis[1,2,5]thiadiazole unit into PBDTBBT has significantly altered the optical and electrochemical properties of the polymer. The optical band gap estimated from the onset absorption edge is _1.88 eV and _1.1 eV, respectively for PBDTTBI and PBDTBBT. It is observed that PBDTBBT exhibited a deeper HOMO energy level (_4.06 eV) with strong intramolecular charge transfer interactions. Bulk heterojunction solar cells fabricated with a configuration of ITO/PEDOT:PSS/PBDTBBT:PC71BM/Al exhibited a best power conversion efficiency of 0.67%, with a short circuit current density of 4.9 mA cm_2, an open-circuit voltage of 0.54 V and a fill factor of 25%.