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Shown are transfer characteristics (open circles) of different ambipolar OLEFETs at a constant drain voltage of . Together with the current/voltage characteristics the position of the recombination zone is shown, as indicated by the arrows. The pixel brightness in the -characteristics in (a)–(c) equals the emitted light intensity shown in (d). For coding the respective shades are displayed on the right side of (d). For better comparability, in (d) the emitted intensity from the three devices are comprised. The device setups are as follows: (a) Top gate, bottom contact: Au (source, drain)/F8BT/PMMA/Au (gate). (b) Bottom gate, top contact: /PVCH/ditetracene/Au (source, drain). (c) Bottom gate, top contact: /PVCH/ditetracene/Ca (source)/Au (drain).
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Sketch of the contact formation between the organic semiconductor ditetracene and the contact materials calcium and gold. The semiconductor is assumed to be intrinsic. Due to the alignment of the Fermi levels through the contact formation, charge carrier reservoirs of electrons and holes are established near the calcium and gold electrode, respectively. (: work function, IP: ionization potential, and EA: electron affinity.)
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In this letter the effect of the charge carrier injection on the performance of ambipolar light-emitting organic field-effect transistors will be investigated. For the analysis, the light output and spatial information of the recombination zone from different devices will be compared. The three investigated devices provide either Ohmic contacts for one or both charge carrier types or hindered injection for both. It will be demonstrated that the light emission in the different operation regimes of the transistor can be used to characterize the contact properties at source and drain.
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