Long-term, intermittent testing of sandwich polymer light-emitting electrochemical cells

The long-term luminance decay of sandwich polymer light-emitting electrochemical cells has been investigated. The cells have been operated multiple times over a period of four months, all under a constant current density of 167 mA/cm². In-between the constant-current runs, the cells were stored at room temperature for up to two months. We identify several factors that affect the luminance and its decay. The peak luminance reached during the virgin runs decreases if the cells are stored after the deposition of the top electrode. During operation, the luminance also decreases after reaching a peak value. However, extended storage at room temperature leads to the recovery of the peak luminance. The luminance recovery can be attributed to the relaxation of doping which reverses the effect of luminescence quenching. A long term, irreversible luminance decay is also observed and attributed to the formation of non-emitting, non-conductive black spots which leads to the loss of emitting area and an increased effective current density. The results illustrate the importance both On and Off states in characterizing the stability of polymer LECs.