3 March 2003 Optimization of organic semiconductor devices by anode modification
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PEDOT [Poly(3,4-ethylenedioxythiophene)] layers were prepared by electrochemical polymerization of the respective monomer. Thereafter, these layers were electrochemically adjusted to different equilibrium potentials and they were investigated with Kelvin Probe measurements. A change in work function could be observed yielding a linear correlation with the pre-adjusted electrochemical potential. These PEDOT layers have been utilized in OLEDs in their accessible range of work functions. Internal energy conditions of the OLEDs were characterized in a photovoltaic setup yielding a linear correlation of the open circuit voltage on the pre-adjusted potential. In a second step the efficiency was determined for devices with Ca cathode (space-charge-limited electron current) as well as for devices with Al cathode (injection-limited electron current). These devices could be optimized in efficiency by adjusting the hole current to the electron current, which was determined by the work function of the cathodic metal. The optimum could be explained in zero-order approximation in terms of a balanced bimolecular reaction between holes and electrons.
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Holger Frohne, David C. Muller, Nina Reckefuss, Paula Rudati, Klaus Meerholz, "Optimization of organic semiconductor devices by anode modification", Proc. SPIE 4800, Organic Light-Emitting Materials and Devices VI, (3 March 2003); doi: 10.1117/12.451856; https://doi.org/10.1117/12.451856

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