Highly efficient organic devices based on electrically doped transport layers

Institut für Angewandte Photophysik, Technische Universität Dresden, 01062 Dresden, Germany.
Chemical Reviews (Impact Factor: 45.66). 05/2007; 107(4):1233-71. DOI: 10.1021/cr050156n
Source: PubMed
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    ABSTRACT: Calculations at HF, DFT (CAM-B3LYP) and MP2 level were carried out with a 6-31+G(d,p) basis set to estimate the polarizability α, the first β and second hyperpolarizability γ and reorganization energy λ of 4,5-dicyanoimidazole chromophore 1 and derivatives formed by adding a benzene ring 2, a π bond containing bridge plus a benzene ring (styryl) 3, and a biphenyl 4. Three different donors electron groups D were attached at the para position of the rings or to the chromophore. Our results showed that the 〈α〉, βtotal and 〈γ〉 values increased as D: H < OCH3 < N(CH3)2. These properties were enhanced when the intra-molecular charge transference was increased due to the substitution of double bonds by aromatic rings in the bridge or by increasing the donor strength of the D group. The increase in the (hyper)polarizability was accompanied by a decrease in the HOMO–LUMO energy gap in agreement with the Valence-Bond Charge-Transfer and sum-over-states models. The reorganization energy data showed that this parameter for electron (λe) and hole transport (λh) for the substituted chromophore (D: OCH3), molecule 3 (D: H and OCH3) and 4 (D: H) are very close to each other. Then, all them should have good charge transport balance performance. Molecule 2 (D: H) showed the smallest λe and higher λh and can be used as electron transfer material, while molecule 3[D: N(CH3)2] showed a small λh, and can be employed as hole transfer material.
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    ABSTRACT: Molecular doping of conjugated polymers represents an important strategy for improving organic electronic devices. However, the widely reported low efficiency of doping remains a crucial limitation to obtain high performance. Here we investigate how charge transfer between dopant and donor–acceptor copolymers is affected by the spatial arrangement of the dopant molecule with respect to the copolymer repeat unit. We p-dope a donor–acceptor copolymer and probe its charge-sensitive molecular vibrations in films by infrared spectroscopy. We find that, compared with a related homopolymer, a four times higher dopant/polymer molar ratio is needed to observe signatures of charges. By DFT methods, we simulate the vibrational spectra, moving the dopant along the copolymer backbone and finding that efficient charge transfer occurs only when the dopant is close to the donor moiety. Our results show that the donor–acceptor structure poses an obstacle to efficient doping, with the acceptor moiety being inactive for p-type doping.
    Nature Communications 03/2015; 6:6460. DOI:10.1038/ncomms7460 · 10.74 Impact Factor
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    ABSTRACT: The adaptation of interfacial layers to the stacked architecture of organic solar cells represents a very useful strategy for improved device operation. In this context, heteroacenic structures such as carbazolocarbazoles have been doped and evaluated as hole transporting materials in small molecule solar cell with either inverted or conventional architecture. S-kinks in the IV-curve detected for the inverted solar cells could be remarkably corrected by reversing the deposition sequence, highlighting the importance of buffer layer adjustment. Some of the studied carbazolocarbazoles proved to be a suitable molecule to be used as hole transporting materials.
    Organic Electronics 02/2015; 17:28-32. DOI:10.1016/j.orgel.2014.11.013 · 3.68 Impact Factor