The role of spontaneous orientation polarization on charge storage behavior at an interface between organic semiconductor layers

Understanding charge carrier dynamics, including carrier accumulation, storage, and extraction, in an organic solid-state film is crucial for improving the performance of organic semiconductor devices such as organic light-emitting diodes and organic photovoltaics. In particular, spontaneous orientation polarization (SOP) induced by a polar organic molecule strongly influences these charge carrier behaviors directly because the SOP can induce a strong internal electric field in thin films. Herein, we clarified the role of SOP in the charge storage ability at the interface between polar organic layers. The charge carrier lifetime was improved when the charge carriers were accumulated at the interface between two layers with positive and negative SOP polarity, whereas a poor storage characteristic was obtained in the case of charge accumulation at the interface between two layers with the same SOP polarity. The results underline that the polarization difference at the charge accumulation interface determines the charge carrier lifetime in organic semiconductor devices. Optically generated carriers are pinned at the organic/organic interface if the two organic layers have a large polarization difference, underlining that the combination of polar molecules is crucial to extend the carrier lifetime.