Stress Testing Polymer Light‐Emitting Electrochemical Cells: Suppression of Voltage Drift and Black Spot Formation

Abstract The stress characteristics of the polymer light‐emitting electrochemical cells (PLECs) are comprehensively evaluated by varying a host of material and operational parameters. PLECs with the lowest salt concentration of less than 2.5% exhibit runaway voltage drift that leads to rapid cell destruction. PLECs with the lowest electrolyte polymer concentration and a 5% salt content exhibit the longest luminance half‐life, but are slow to activate and are plagued by black spots. At moderate‐to‐high electrolyte concentrations, the PLECs are relatively stable but are not immune to black spots and voltage drift. A lifetime figure‐of‐merit is introduced to quantitatively account for all three indicators of cell degradation in luminance decay, voltage drift, and black spot formation. A surprising discovery is that voltage drift and black spot formation can be effectively suppressed by drastically increasing the electrolyte content. A cell with a 70% electrolyte content exhibits the best lifetime of nearly 350 h when operated at a constant current density of 167 mA cm⁻². The black spots can also be effectively eliminated by employing silver instead of aluminum as the cathode material.