Large-area Two-dimensional Organic Single Crystals:The Growth Strategy And Application In Organic Field-effect Transistors

Two-dimensional organic single crystals are long-range ordered films of monolayer or few-layered organic molecules held together by weak interaction(Vander Waals,π-π interaction,hydrogen bonding,etc.).Two-dimensional organic single crystals(2DOSCs)are characterized by the combination of the easy integration property of large-area polycrystalline thin films and perfect molecular order of organic single crystals,which makes 2DOSCs ideal tools to study the intrinsic charge transport property of organic semiconductors.2DOSCs are also expected to produce high-performance large-area devices and circuits for commercial applications.However,it remains challenging to develop a effective and controllable method to produce high-quality two-dimensional organic single crystal.This thesis focuses on the controllable growth and charge transfer properties of two-dimensional organic single crystals,the details are given as follows:Firstly,we developed a simple,yet effective method to grow large-area 2DOSCs.This novel method was named "space-confined self-assembly"(SCS),which meets the two requirements of the growth of large-area 2DOSCs:(i)low density of nuclei.(ii)two-dimensional crystal growth mode.We chose water surface as substrate to minimize the density of nuclei.Furthermore,we regulate the interfacial tension of solution/water by choosing a suitable surfactant,i.e.,tetrabutyl ammonium bromide(TBAB),to increase the spreading area of the solution on water surface,and thus confine the crystal growth within 2D.Sub-centimeter sized 2DOSCs we obtained at the assist of TBAB.The general applicability of this method was demonstrated by several organic semiconductors with different molecular structures.The quality of 2DOSCs was characterized by polarized optical microscope(POM),transmission electron microscopy(TEM)and selected-area electron diffraction(SAED),indicating the high crystallinity of 2DOSCs.The mobility of the organic field-effect transistor(OFETs)based on 2DOSCs is one of the highest value reported,demonstrating the high-quality nature of as-grown 2DOSCs.Secondly,The polymer assisted solvent vapor annealing(PASVA)method was developed for the growth of largr-area high-quality arrays of 2DOSCs.The growth mechanism of large-area high-quality 2D arrays of 2DOSCs,and their application in optoelectronic devices were studied.The quality of the 2D organic single crystal array was characterized by atomic force microscope(AFM),POM and XRD,showing that the quality of the polymer-assisted self-assembled organic single array is higher than those without polymers.OFETs based on 2D organic single crystal array showed that polymer-assisted organic single crystal arrays have higher performance than polymer-free organic single crystal arrays,indicating that the polymers play an important role in the growth of high quality 2D organic single crystal arrays.PASVA provides an effective way to grow large area of two-dimensional organic single crystal arrays.