Dynamic doping in bright and stable light emitting electrochemical cells.

By using fast current density and luminance versus voltage (JL-V) analysis the device operation of sandwiched light emitting electrochemical cells (LECs) during their normal voltage driving operation mode is studied. In LECs the application of a voltage results in the movement of ions changing the state of the device, as a result the JL-V scans need to be performed fast and meet certain conditions to be meaningful. Space-charge limited current behavior is observed once the injection barriers are overcome. The increase of the current density after this point imply that the effective thickness of the devices is reduced which indicates the formation of more conductive regions adjacent to the electrodes. The increase in conductivity is a consequence of compensation of the injected electrons by dissociated ions that effectively increase the carrier concentration similar like in electrochemically doped semiconductors. The extension of the dynamically doped regions can be controlled by applying a pulsed current driving scheme which allows for both sub-second turn-on time and long lifetimes.