Understanding of The Nanosprouts Structure Inhomogeneity
of Organic Semiconductor and The Corresponding Optical Memory Property

The structure inhomogeneity of organic semiconductors had been widely observed in organic polycrystal or amorphous films. Detailed understanding of the crystal packing modes and orientations of these structure inhomogeneities has the potential to guide the design of advanced organic electrical, optical, mechanical, or magnetic devices for the corresponding properties difference of lattice planes. The identification of the crystal packing modes and orientations of organic inhomogeneity structures is a challenging part to research community for the limitations of commonly used characterization methods. For instance, X-ray diffraction can only identify the presence of these inhomogeneity structures but cannot be used to detect the specific packing mode and orientation of each structure; STEM, the commonly used method in inorganic materials show limited performance in organic materials for the severe damage of high-energy electrons to organic materials. Here in, we report a characterization approach which provides local structure information of organic thin films over a large area.<br/>In this talk, a low damage, organic materials compatible characterization method-lateral force microscope test will be introduced. Detailed characterization results of the crystal packing mode and orientation of a commonly used evaporation-based 2,9-Diphenyl-dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (2,9-Dph-DNTT) organic film will be showed; the two inhomogeneity structures in the film-nanosprouts structure and terrace structure are corresponding to the molecular “face on” packing mode and “face up” packing mode, respectively. The electrical performance difference of the two nanostructures will be studied by conductive atomic force microscope test. The temperature dependent formation mechanism of the two structures will also be discussed in detailed.<br/>Apart from the properties difference, the structure inhomogeneities in organic materials also have the potential to generate other interesting phenomenon, for instance, optical memory phenomenon for the charge trapping centers induced by the lattice mismatch in the interface of the inhomogeneity structures. Non-volatile optical memory transistor (OMT) based on the nanosprouts structure of 2,9-Dph-DNTT film is developed, combining with Al₂O₃ high-k dielectric, the OMT showed low operating voltage (less than 4V) and decent field effect mobility up to 3cm²V^-1s^-1 and promising data retention performance of binary states current ratio higher than 10⁴ for more than 12hours, the mechanism of the optical-electrical memory phenomenon will be discussed in detailed. At last, a demonstration of a 16×16 flexible low operating voltage active matrix OMT array of 45ppi with image processing capability will be showed.