High resolution scanning optical imaging of a frozen planar polymer light-emitting electrochemical cell: an experimental and modelling study

Light-emitting electrochemical cells (LECs) are organic photonic devices based on a mixed electronic and ionic conductor. The active layer of a polymer-based LEC consists of a luminescent polymer, an ion-solvating/transport polymer, and a compatible salt. The LEC p-n or p-i-n junction is ultimately responsible for the LEC performance. The LEC junction, however, is still poorly understood due to the difficulties of characterizing a dynamic-junction LEC. In this paper, we present an experimental and modeling study of the LEC junction using scanning optical imaging techniques. Planar LECs with an interelectrode spacing of 560 mu m have been fabricated, activated, frozen and scanned using a focused laser beam. The optical-beam-induced-current (OBIC) and photoluminescence (PL) data have been recorded as a function of beam location. The OBIC profile has been simulated in COMSOL that allowed for the determination of the doping concentration and the depletion width of the LEC junction.