Reversible luminance decay in polymer light-emitting electrochemical cells

The luminance decay of generic sandwich polymer light-emitting electrochemical cells has been investigated. Under constant current operation, the apparent luminance decay is caused by both the formation of non-emitting black spots, which decreases the active emitting area, and the in situ electrochemical doping, which quenches the luminescence of the light-emitting electrochemical cell film. The latter's effect on luminance, however, can be mostly reversed by letting the electrochemical doping relax. A dramatic recovery of luminance is observed when the device is stored without voltage bias and/or moderately heated between consecutive operations. The decay/recovery cycle can be repeated multiple times with little loss of luminance despite the high current density (167 mA/cm²) applied. At lower current density, a freshly made device loses less than 10% of its peak luminance after over 200 h of continuous operation. Polymer light-emitting electrochemical cells therefore possess vastly longer operating lifetime if allowed to recover from the effect of reversible doping.