Electric field redistribution on light-emitting devices based on Langmuir–Blodgett films of a porphyrin derivative

Transient characteristics of light-emitting devices have been studied in this article. The devices have been fabricated using Langmuir–Blodgett films of a porphyrin derivative. Transient electroluminescence (EL) response has been studied by applying a sequence of two rectangular voltage pulses. The field redistribution in the devices has further been studied by time-of-flight technique in the integral mode, where the photosignal corresponds to the collected charges on the electrodes. The transient EL response of the device has been compared with the field in the device. The striking similarity between the transient EL characteristics and collected charge showed that the transient EL directly follows the electric field variation in the device. Electric field redistribution due to trapped charges has been suggested to explain the transient EL results. The photogenerated signal is directly proportional to the field in the device and has been used to probe the relative changes of the field during and after the application of the voltage pulse.