Lifetime limitations in organic electronic devices due to metal electrochemical migration
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Research Letter
Lifetime limitations in organic electronic devices due to metal electrochemical migration Robert Abbel, Linda van de Peppel, and Gerwin Kirchner, Holst Centre – TNO, High Tech Campus 31, 5656 AE Eindhoven, The Netherlands Jasper J. Michels, Max Plack Institut für Polymerenforschung, Ackermannweg 10, 55128 Mainz, Germany Pim Groen, Holst Centre – TNO, High Tech Campus 31, 5656 AE Eindhoven, The Netherlands; Delft University of Technology, Faculty of Aerospace Engineering, Kluyverweg 1, 2629 HS Delft, The Netherlands Address all correspondence to Pim Groen, Jasper J. Michels at [email protected], [email protected] (Received 6 April 2017; accepted 16 June 2017)
Abstract Operational lifetime is a critical performance parameter of organic electronic devices and can be cut short by multiple degradation mechanisms. One supposed cause is metal migration between the electrodes, which, however, is difficult to study independently of other failure modes. We present a setup, which excludes such competing processes and demonstrates that silver (Ag) electrochemical migration through organic optoelectronic materials occurs predominantly by cation transport. Metal dendrites form at the cathode, eventually causing short circuits between the electrodes. Lifetime studies with organic light-emitting diodes containing Ag electrodes suggest that results obtained with our setup can provide relevant information about degradation in real devices.
Introduction The phenomenon of metals migrating under the influence of DC electric fields and currents is well known for decades and has been studied intensely in the microelectronics and electroceramics industries.[1,2] This research has demonstrated that silver (Ag) is particularly prone to such behavior, especially in the presence of humidity.[1,3] One proposed mechanism is electrochemical migration, i.e., the oxidation of Ag at the anode into Ag+ cations, which then follow the electric field and are electrochemically reduced back to zerovalent metal upon contact with the cathode.[3,4] In other systems, momentum transfer from moving charge carriers to metal atoms, which are consequently pushed forward by an “electron wind” or “hole wind” has been demonstrated as the predominant cause.[2,5] This latter mechanism is typically referred to as electromigration, to distinguish it from electrochemical migration. Silver is frequently employed in the electrodes of organic optoelectronic devices, such as organic light-emitting diodes (OLEDs) and photovoltaic cells. It is used as a continuous film, as Ag nanowire network or as shunting lines to reduce the resistive losses of transparent electrodes with insufficient intrinsic conductivities [Fig. 1(a–c)].[6] Short circuiting by electrically induced Ag migration might therefore contribute to the limited lifetimes of organic optoelectronic devices containing Ag in one or both electrodes. Until now, however, studies dedicated to such migration processes within these device architectures have been rather scarce; those few published yielding
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