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 μm 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.