Zur Ladungstrennung bei der sensibilisierten Löcherinjektion in Anthracenkristallen / Charge Separation and Sensitized Hole Injection into Anthracene Crystals

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Abstract
The dependence of the sensitized injection current and of the crystal's sensitized delayed fluorescence on the electric and magnetic field is utilized to examine the process of charge separa-tion at the phase boundary crystal/water electrode. Hole currents, sensitized by electron transfer interaction between rhodamine B molecules in their lowest excited singlet state and the anthracene crystal, can be shown to originate from a thermal injection process. This conclusion is further supported by the changed phenomenology of the injection current and the delayed fluorescence in the presence of molecular oxygen in the aqueous electrode. In this case an alternative injection reaction predominates due to the oxygen enhancement of the intersystem crossing rate and thus of the sensitized population of triplet excitons in the crystal, the latter ones injecting holes through electron transfer to oxygen present at the surface. Neglecting image-and Coulomb forces at the interface crystal/electrolyte, an analytical ex-pression for the current-voltage relation can be given which includes the influence of the space charge. This expression does well agree with the experimental current-voltage characteristics ob-served for different surface recombination rates of charge carriers.

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