Abstract
With the aim of pushing the knowledge and understanding on mixed films of organic semiconductors forward, blends of ZnPC and F8ZnPC in different ratios are manufactured. The films have a polycrystalline structure, as indicated by electron diffraction profiles and infrared-spectroscopy. Photoluminescence data show completely different spectra for the blends, compared to the pure materials, which can be ascribed to the suppressing of excimer formation and the appearance of a new charge-transfer excitation between the two different molecules in the blends. This new excitation can also be seen in optical absorption. Momentum dependent measurements of the electronic excitations by electron energy-loss spectroscopy confirm the localized character of the new charge-transfer excitation in the blends. Our experimental data help understand the important issue of donor/acceptor coupling in organic semiconductors.
Highlights
Momentum dependent measurements of the electronic excitations by electron energy-loss spectroscopy confirm the localized character of the new charge-transfer excitation in the blends
Semiconductor devices have become an integral part of the daily life, and for some years organic semiconductor devices have become increasingly present, e.g., as organic light emitting diodes (OLEDs) for displays in smartphones or TVs
The top curve shows the spectrum of pure ZnPC, followed by those for the various blends and pure F8ZnPC as indicated
Summary
Semiconductor devices have become an integral part of the daily life, and for some years organic semiconductor devices have become increasingly present, e.g., as organic light emitting diodes (OLEDs) for displays in smartphones or TVs. To realize efficient devices, it is essential to create perfectly adapted energy structures, regardless of the material. While first indications showed tunability in organic solar cells in 2013,1 Schwarze et al showed in 20162 that a controlled shift of the ionization energy (IE) can be achieved in organic semiconductors by mixing molecules with a halogenated derivative. This effect is based on interactions of excess charge carriers with the quadrupole field in the thin film. These materials are known, inter alia, as absorber and donor materials in organic solar cells[4,5,6,7,8] but are employed in OLEDs.[9,10] The fluorinated derivatives are characterized by the fact that the fluorination shifts the energy levels down with respect to the vacuum level, while the strength of the shift depends on the number of fluorine atoms.[11,12]
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