Capacitance measurements of junction formation and structure in polymer light-emitting electrochemical cells

We present capacitance–voltage and current–voltage measurements of polymer light-emitting electrochemical cells and compare these results with steady state device model calculations. The capacitance–voltage characteristic is used to assess the formation and structure of the electrochemical junction in the device. The cell capacitance and current both increase sharply above a threshold voltage as the bias is increased. The threshold voltage for the rapid increase in capacitance is lower than that for the increase in current, indicating that the electrochemical junction begins to form prior to significant current flow. The electrochemical junction width, estimated from the capacitance measurements, is about 15 nm at a current density of $\text{0.1\hspace{0.17em}}{\mathrm{A/cm}}^{\mathrm{2}}.$ The steady state device model calculations are in reasonable agreement with these observations.