Synthesis and Characterization of Tricyanovinyl-Capped Oligothiophenes as Low-Band-Gap Organic Materials

Pappenfus, Ted M.; Burand, Michael W.; Janzen, Daron E.; Mann, Kent R.

doi:10.1021/ol034317q

Cited by 68 publications

(32 citation statements)

References 25 publications

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“…On the other hand, terminal substitution with strong D/A groups can have a very large effect on small oligomers in generating small bandgaps (Meier, 2005), however this effect will vanish at the polymer limit (Meier, 2005; Gierschner et al, 2007). This is also true for the recently discussed dicyano- (Pina et al, 2006) or dicyanovinyl-thiophene (DCV n T) series (Pappenfus et al, 2003; Schulze et al, 2006), see Figure 4. A secondary effect in this category is the promotion of dense packing in the solid state by minimizing the disorder, which significantly lowers the effective optical bandgap due to enhancement of the anisotropic polarizability of the material via closely packed parallel chains (Egelhaaf et al, 2002), whereas H/J-aggregation play only a very minor role in polymers (Gierschner et al, 2009).…”

Section: Key Parameters Of Bandgap Engineeringsupporting

confidence: 57%

Computational engineering of low bandgap copolymers

2013

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We present a conceptual approach to low bandgap copolymers, in which we clarify the physical parameters which control the optical bandgap, develop a fundamental understanding of bandgap tuning, unify the terminology, and outline the minimum requirements for accurate prediction of polymer bandgaps from those of finite length oligomers via extrapolation. We then test the predictive power of several popular hybrid and long-range corrected (LC) DFT functionals when applied to this task by careful comparison to experimental studies of homo- and co-oligomer series. These tests identify offset-corrected M06HF, with 100% HF exchange, as a useful alternative to the poor performance of tested hybrid and LC functionals with lower fractions of HF exchange (B3LYP, CAM-B3LYP, optimally-tuned LC-BLYP, BHLYP), which all significantly overestimate changes in bandgap as a function of system size.

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Section: Key Parameters Of Bandgap Engineeringsupporting

confidence: 57%

Computational engineering of low bandgap copolymers

2013

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“…[10] The absorption gap for a dilute solution in CH 2 Cl 2 is narrowed by approximately 1 eV, compared to the molecule without the dicyanovinyl end groups. [11] Similar derivatives of terthiophene and sexithiophene with tricyanovinyl end groups (TCV3T and TCV6T) have recently been reported by Pappenfus et al [11] However, the effect of tricyanovinyl is so strong that these oligomers have an even higher electron affinity than C 60 . They appear therefore hardly suitable for solar cell applications since the open circuit voltage of organic solar cells scales with the difference between the LUMO energy of the acceptor and the HOMO energy of the donor.…”

Section: Characterization Of Dcv3t In Solution and Thin Filmssupporting

confidence: 52%

Organic Thin‐Film Photovoltaic Cells Based on Oligothiophenes with Reduced Bandgap

Uhrich¹,

Schueppel²,

Petrich³

et al. 2007

Adv Funct Materials

165

132

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The best polymeric solar cells reported so far are based on a so‐called bulk heterojunction of a polythiophene as donor and a soluble fullerene derivative as acceptor. However, these cells still suffer from an unsatisfying photovoltage, typically below 0.7 V. Here, we show that we can achieve higher photovoltages using a new terthiophene end‐capped with electron withdrawing dicyanovinyl groups (DCV3T) that increase both the ionization energy and even more strongly the electron affinity of the compound. The new material is tested in cells using a photoactive heterojunction to separate the excitons generated in the oligomer and a p‐doped wide‐gap transport layer. The solar cells show an open circuit voltage of up to 1.04 V and a broad spectral sensitivity band ranging from 420 nm to 650 nm. Solar cells based on such oligothiophenes are promising candidates for stacked organic solar cells tailored to the sun‐spectrum. Moreover, we present first examples of a new concept for organic solar cells: By blending DCV3T with fullerene C60, an enhanced generation of triplet excitons on the oligomer can be achieved via a back and forth transfer of excitons (ping‐pong‐effect).

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“…With such acceptors, the LUMO wave function is expected to localize on the acceptor group rather than the oligomer backbone. This was demonstrated, e.g., for tricyanovinyl ͑TCV͒-capped oligothiophenes, 14,15 where the LUMO energy is solely determined ͑i.e., fixed͒ by the strong TCV acceptor group and becomes independent of backbone modifications ͑such as chain length variations͒.…”

Section: Introductionmentioning

confidence: 94%

Optimizing organic photovoltaics using tailored heterojunctions: A photoinduced absorption study of oligothiophenes with low band gaps

et al. 2008

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A power conversion efficiency of 3.4% with an open-circuit voltage of 1 V was recently demonstrated in a thin film solar cell utilizing fullerene C 60 as acceptor and a new acceptor-substituted oligothiophene with an optical gap of 1.77 eV as donor ͓K. Schulze et al., Adv. Mater. ͑Weinheim, Ger.͒ 18, 2872 ͑2006͔͒. This prompted us to systematically study the energy-and electron transfer processes at the oligothiophene:fullerene heterojunction for a homologous series of these oligothiophenes. Cyclic voltammetry and ultraviolet photoelectron spectroscopy data show that the heterojunction is modified due to tuning of the highest occupied molecular orbital energy for different oligothiophene chain lengths, while the lowest unoccupied molecular orbital energy remains essentially fixed due to the presence of electron-withdrawing end groups ͑dicyanovinyl͒ attached to the oligothiophene. Use of photoinduced absorption ͑PA͒ allows the study of the electron transfer process at the heterojunction to C 60. Quantum-chemical calculations performed at the density functional theory and/or time-dependent density functional theory level and cation absorption spectra of diluted DCVnT provide an unambiguous identification of the transitions observed in the PA spectra. Upon increasing the effective energy gap of the donor-acceptor pair by increasing the ionization energy of the donor, photoinduced electron transfer is eventually replaced with energy transfer, which alters the photovoltaic operation conditions. The optimum open-circuit voltage of a solar cell is thus a trade-off between efficient charge separation at the interface and maximized effective gap. It appears that the open-circuit voltages of 1.0-1.1 V in our solar cell devices have reached an optimum since higher voltages result in a loss in charge separation efficiency.

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Synthesis and Characterization of Tricyanovinyl-Capped Oligothiophenes as Low-Band-Gap Organic Materials

Cited by 68 publications

References 25 publications

Computational engineering of low bandgap copolymers

Computational engineering of low bandgap copolymers

Organic Thin‐Film Photovoltaic Cells Based on Oligothiophenes with Reduced Bandgap

Optimizing organic photovoltaics using tailored heterojunctions: A photoinduced absorption study of oligothiophenes with low band gaps

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