Construction And Optoelectronic Properties Of 2D Organic Semiconductor Single-crystalline Heterojunctions

Two-dimensional（2D）organic semiconductor single-crystalline heterojunction combine the characteristics of 2D organic single crystal and heterojunction,which is not only a powerful tool for studying the intrinsic optoelectronic properties of organic semiconductor materials,but also an important structure to prepare high-performance organic field effect transistors（OFETs）,organic photodetectors（OPDs）,rectifier diodes and other devices.This paper focuses on the research of 2D organic semiconductor single-crystalline heterojunction,develops new preparation methods,and explores its optoelectronic properties and device applications.The main research contents are as follows:1.A soft template assisted self-assembly strategy is developed and high-quality2D organic single crystals（2DOSCs）are successfully prepared.The surfactant used in this strategy can reduce the surface tension of water and prevent the excessive and discontinuous spreading of the solution when it meets the solution with low surface tension.In the case of high surface tension solution,the surfactant used as a soft template to play a supporting layer and promote the full and continuous spread of the solution on the water surface.This strategy overcomes the influence of solvent surface tension on the crystallization process of liquid substrate,and successfully prepares a variety of 2D organic semiconductor single crystals,which lays a foundation for the further preparation of 2D organic semiconductor single-crystalline heterojunctions.2.A strategy of fabricating high-performance organic phototransistors（OPTs）using type Ⅰ 2D organic semiconductor single-crystalline heterojunctions with several molecular layers is proposed.Type I 2D organic semiconductor single-crystalline heterojunctions with several molecular layers of thickness have been successfully fabricated by layer-by-layer transfer method.Benefiting from molecular-level thickness of the 2DOSCs and the favorable band structure of type Ⅰ heterojunction,OPTs show a high responsivity up to 891.4 A W^-1,external quantum efficiency up to 3.03×10⁵,photosensitivity and specific detectivity up to 5.9×10⁷and 2.5×10¹⁶ Jones,all of which are the highest values among OPTs based on planar heterojunctions reported in the literature to date.3.A diode with a novel asymmetric structure based on type Ⅱ 2D organic single-crystalline heterojunctions is designed.The device with asymmetric structure overcomes the problem of low forward current in traditional devices with symmetrical structure.In addition,2DOSCs with molecular-scale thickness have high efficiency of gate-controllable and effectively supress reverse current.Consequently,the maximum rectification ratio of the type Ⅱ 2D organic single-crystalline p-n junction diode with asymmetric device structure is up to 1.93×10⁸,which is the highest value among the known gate-tunable rectifiers.In addition,by changing the gate voltage,the rectification ratio can be greatly regulated in the range of 5.75 to 1.93×10⁸.4.A organic single crystal heteroepitaxial strategy is developed to prepare high quality 2D organic semiconductor single-crystalline heterojunctions with well-defined orientation.In this strategy,the 2DOSC of one organic semiconductor is used as a template to induce epitaxial growth of another single crystal,avoiding the problems of interface contamination and random crystal orientation in the layer-by-layer transfer method.OFETs based on the well-oriented 2D organic semiconductor single-crystalline heterojunctions show excellent ambipolar charge transport performance,the maximum electron mobility is 1.82 cm^-2 V^-1 s^-1 and the maximum hole mobility is 2.22 cm^-2 V^-1 s^-1,which are among the highest values in ambipolar OFETs based on bilayer organic heterojunctions.