(a) Conceptual illustration of an OLEB suitable for direct visualization of conductance. (b) Schematic of a device structure of a parallel alternating-current electroluminescent (AC EL) and a high-resolution cross-sectional transmission electron microscopy (TEM) image of the device. The scale bar is 100 nm. (c) The time-resolved EL signals of two light-emitting units (LEUs) of a parallel AC EL device under alternating-current voltage with a frequency of 1 kHz. Solid and dot black lines correspond to the electric fields imposed to (LEU) 1 and 2, respectively on alternating-current operation. Light emits only at the negative polarity for each LEU. (d) Luminance versus voltage (L–V) characteristic of a parallel AC EL device at different frequencies.