Charging and discharging of a planar polymer light-emitting electrochemical cell

Planar polymer light-emitting electrochemical cells (LECs) with an interelectrode gap size of 670 μm and 495 μm have been activated by applying a fixed voltage bias of 20 V at a temperature of 340 K to enable them to reach different terminal currents before being discharged under short-circuit conditions. These discharging, or dedoping currents have been monitored for an extended period during which they have decreased by five orders of magnitude. The total dedoping charge has been determined by integrating the time-dependent dedoping current, which allows for the calculation of the cell's doping level. The data suggest that some additional doping has occurred after the formation of the LEC junction. The overall level of doping, however, is not strongly affected by the large amount charges injected after junction formation. In fact, the total dedoping charge can be approximated as the amount of injected charge, up to the moment of junction formation. The total dedoping charge, however, is sensitive to the interelectrode gap size of the planar cells. The results demonstrate the feasibility of detecting the minute discharging current of a large planar LEC down to pA level. The ability to determine the dedoping charge and its dependence on various operational and device-related parameters provides additional tools to facilitate understanding of the complex doping and dedoping processes in a polymer LEC.