Transient bleaching pulse shapes in electrochromic polysiloxane thin films

Transient bleaching currents are examined for a series of electrochromic carbazole-modified polysiloxane thin films. The shape of the bleaching currents is found to be sensitive to the type of counter-ion employed and the initial density of counter-ion charge that is deposited in the films during the colouration stage. Pure space-charge-limited (SCL) transport of counter-ions that posses a well-defined mobility is inconsistent with the observed pulse shapes and a modified SCL model that involves fast and slow mobility sites is proposed. The modified SCL model may describe a variety of transient bleaching pulse shapes (including current overshoots) as charge is removed from the electrochromic films and the counter-ions are constrained to transfer from slow to fast discharge sites.