The Preparation Of N-type Ultra-thin Two-dimensional Crystals Of Organic Semiconductors And Their Photoelectric Devices

Due to the large-area,low-cost,low-temperature preparation and potential application prospects of flexible organic electronic products,organic field-effect transistors(OFETs),which are one of the most widely used and most important electrical components,have become the forefront research field of organic electronics.Large-area ultra-thin two-dimensional(2D)single crystals of organic semiconductors(2DCOS),which combine the advantages of long-range ordered non-grain boundary in organic single crystals and good flexibility of 2D materials,are regarded as the best choice to reveal the intrinsic properties of organic semiconductors,build high-performance transistor devices and fabricate the large-scale integrated flexible circuits.At the same time,ultra-thin 2DCOS are also expected to exhibit optoelectronic properties that are not achievable with some three-dimensional bulk materials.This paper is mainly based on the growth of ultra-thin 2DCOS and its high-performance optoelectronic devices.The main contents are as follows:1.Through the molecular design,three kinds of 2DCOS of n-type organic semiconductors were grown on the water surface,namely furanthiophene sample(TFT-CN)and quinolone oligothiophene sample(2DQTT-o-B)and 2-(1,3-dithiol-2-ylidene)malononitrile-based sample(NDI3HU-DTYM2).The size of the 2DCOS was up to the millimeter and the thickness was few molecular layers.Furthermore,the silver/gold composite electrodes were used instead of the conventional single metal to protect the stability of the electrode while achieving work function matching.The prepared TFT-CN 2DCOS-based OFETs exhibited a maximum mobility of 1.36 cm² V^-1s^-1,an average of 1.08 cm² V^-1s^-1,and a switching ratio of up to 10⁸ in the room temperature atmosphere,which was one of the highest performance in literatures.2.In this paper,by carefully designing and selecting an infrared-sensitive organic material,an infrared phototransistor ultra-high sensitivity was prepared based on TFT-CN 2DCOS with a thickness of only 4.8 nm.The light-controlled transistor exhibited high responsivity of 9�10⁴ A W^-1 and external quantum efficiency of 4�10⁶%under the illumination of the near-infrared light intensity of 179.5?W cm^-2 in the saturation region.More importantly,the 2DCOS-based phototransistor exhibited a high sensitivity of 5�10⁵and a detectivity of 6�10¹⁴Jones in the infrared region.Furthermore,comparing with the 32 nm micro-nanocrystals prepared by the same method,it can be proved that the 2DCOS-based device can effectively enhance the gate voltage stability of the transistors and work in the fully depleted layer,thereby obtaining the extremely low off-state dark current(0.3 p A),which proved that 2DCOS was an ideal material for preparing highly sensitive photo-controlled transistors.3.In this paper,a complementary low-voltage circuits composed by 2DCOS was prepared with the p-type and n-type transistors.Firstly,a single-layer TFT-CN 2DCOS was prepared with the water surface as substrate,and the thickness was only 1.8 nm.The single-layer TFT-CN 2DCOS-based OFETs exhibited the mobility of 0.8 cm² V^-1s^-1,which was the one of the highest performance in the 2DCOS.With the ultra-flat Al₂O₃as a dielectric layer,and a p-type dioctyl-substituted dibenzo[d,d']thieno[3,2-b;4,5-b']dithiophene(C₈-DBTDT)2DCOS,the construction of a high-performance inverter with low-voltage operation.The inverter was proved to operate in 4V,the gain of 27.