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- Belova, Valentina, et al.
(författare)
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Evidence for Anisotropic Electronic Coupling of Charge Transfer States in Weakly Interacting Organic Semiconductor Mixtures
- 2017
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 139:25, s. 8474-8486
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Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensive investigation of the charge-transfer (CT) effect in weakly interacting organic semiconductor mixtures. The donor-acceptor pair diindenoperylene (DIP) and N,N′-bis(2-ethylhexyl)-1,7-dicyanoperylene-3,4/9,10-bis(dicarboxyimide) (PDIR-CN2) has been chosen as a model system. A wide range of experimental methods was used in order to characterize the structural, optical, electronic, and device properties of the intermolecular interactions. By detailed analysis, we demonstrate that the partial CT in this weakly interacting mixture does not have a strong effect on the ground state and does not generate a hybrid orbital. We also find a strong CT transition in light absorption as well as in photo- and electroluminescence. By using different layer sequences and compositions, we are able to distinguish electronic coupling in-plane vs out-of-plane and, thus, characterize the anisotropy of the CT state. Finally, we discuss the impact of CT exciton generation on charge-carrier transport and on the efficiency of photovoltaic devices.
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| 3. |
- Beyer, Paul, et al.
(författare)
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Fermi level pinned molecular donor/acceptor junctions : Reduction of induced carrier density by interfacial charge transfer complexes
- 2020
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7534 .- 2050-7526. ; 8:43, s. 15199-15207
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Tidskriftsartikel (refereegranskat)abstract
- Increased hole density in an electron donor-type organic semiconductor can be achieved by deposition of a strong acceptor-type molecular layer on top, and has been shown to enable adjusting the carrier density in organic field effect transistors (OFETs). This interfacial charge transfer is due to simultaneous Fermi level (EF) pinning of the donor's highest occupied level and the acceptor's lowest unoccupied level. Here, we investigate the electrical properties of such an EF-pinned junction formed by diindenoperylene (DIP, as donor) and hexafluoro-tetracyano-naphthoquinodimethane (F6, as acceptor) in OFETs, as well as its electronic properties by photoelectron spectroscopy and electrostatic modelling. We find that, in addition to the EF-pinning induced integer charge transfer across the interface, DIP and F6 form charge transfer complexes (CPXs) at their junction. The molecularly thin CPX interlayer acts as insulator and significantly reduces the density of carriers induced on either side of the junction, compared to a scenario without such an interlayer. CPX formation is thus unfavourable for the effectiveness of controlling carrier density at molecular donor/acceptor junctions by EF-pinning. This journal is
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| 5. |
- Hörmann, Ulrich, et al.
(författare)
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Voc from a Morphology Point of View : the Influence of Molecular Orientation on the Open Circuit Voltage of Organic Planar Heterojunction Solar Cells
- 2014
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Ingår i: Journal of physical chemistry C. - : American Chemical Society (ACS). - 1932-7455 .- 1932-7447. ; 118:46, s. 26462-26470
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Tidskriftsartikel (refereegranskat)abstract
- The film morphology and device performance of planar heterojunctionsolar cells based on the molecular donor material α-sexithiophene (6T) are investigated.Planar heterojunctions of 6T with two different acceptor molecules, the C60 fullerene anddiindenoperylene (DIP), have been prepared. The growth temperature of the 6T bottomlayer has been varied between room temperature and 100 °C for each acceptor. By meansof X-ray diffraction and X-ray absorption, we show that the crystallinity and the molecularorientation of 6T is influenced by the preparation conditions and that the 6T filmtemplates the growth of the subsequent acceptor layer. These structural changes areaccompanied by changes in the characteristic parameters of the correspondingphotovoltaic cells. This is most prominently observed as a shift of the open circuitvoltage (Voc): In the case of 6T/C60 heterojunctions, Voc decreases from 0.4 to 0.3 V,approximately, if the growth temperature of 6T is increased from room temperature to 100°C. By contrast, Voc increases from about 1.2 V to almost 1.4 V in the case of 6T/DIP solarcells under the same conditions. We attribute these changes upon substrate heating toincreased recombination in the C60 case while an orientation dependent intermolecular coupling seems to change the origin of the photovoltaic gap in the DIP case.
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