Engineered current path of vertical organic phototransistors for smart optoelectronic applications

As the demands for smart optoelectronics, including photosensor and photomemory, are increasing, multifunctional organic field-effect transistors have been considered as useful candidates for these complex systems. In particular, the vertical-type organic phototransistor (VOPT) is considered more promising for practical optoelectronic applications than the typical lateral-structured devices in terms of electro-optical characteristics and integration density. However, the on/off current ratio and photosensitivity of VOPTs are inherently constrained because of the presence of leakage current that flows along the structurally uncontrollable charge paths. Although considerable effort has been exerted to reduce the leakage current in VOPTs, developing VOPT with a high on/off ratio and photosensitivity remains challenging for practical applications of photosensor and photomemory. In this paper, we proposed a promising strategy for precisely engineering the current path of VOPTs. A charge blocking layer (CBL) is introduced at the interface between the source electrode and organic semiconductor. Its geometrical structure is simply optimized using a self-alignment process to effectively limit the paths of the leakage current. The developed VOPT with CBL presents a highly enhanced on/off current ratio and photosensitivity compared with the typical device. Moreover, our device demonstrates high potential as photodetector and photomemory for smart optoelectronic systems. This novel concept of realizing VOPTs to function as superior photosensor and photomemory can potentially become a fundamental platform for the advancement of next-generation optoelectronics in Internet-of-Things systems.