Transient Photocurrent in Organic Photocells Assisted By Electric Double Layers in Electrolytes

Recently, there has been increasing interest in photoelectric conversion by organic semiconductors. Organic materials have many advantages over inorganic materials, such as the possibility of low temperature, and thus low cost processing, which allows for flexible architectures to be realized. However, to date, organic device performance still lags behind that of inorganic devices. It is our aim to use the intrinsic properties of organic materials to develop novel operation principles for organic devices, to rival the performance of inorganic devices.

In previous works, our group has reported on anomalous transient photocurrents induced by a multi-layer photocell architecture, which incorporates a polarizable insulating layer to aid charge separation in the active semiconductor layer. More recently, we reported the use of ionic liquids as the insulating layer. Such architectures generate a time-varying (transient) response to continuous illumination, which may have an application to optical communication. In these devices, The electric double layers in ionic liquid enhance the charge separation in the active layers and generate an anomalous transient photocurrent.

In this work, we adopted the KCl aqueous solution to the insulating layer, instead of ionic liquids. Figure.1 shows the transient photocurrent with several concentration KCl aqueous solutions. The transient photocurrent was obtained ever with a small amount of KCl. Furthermore, there is a concentration dependence of the peak values and the relaxation times of the transient photocurrents.