Property Investigation And Controllable Growth Of Organic Semiconductor Crystals

Organic semiconductor single crystal provides an ideal platform for studying crystal structure-property relationship,due to its highly ordered molecular arrangements and absence of grain boundaries or defects.Meanwhile,field-effect transistors based on organic semiconductor single crystals can be used as powerful tools for investigating the intrinsic properties of organic semiconductor materials.Organic semiconductor single crystals are dominant factors determining the properties of organic single crystal field-effect transistors.The qualities of organic semiconductor single crystals depend on many factors such as molecular structure,growth method,concentration and so on.Of all these factors,molecular structure is the most important one.Hence,the organic semiconductor materials we choose are the 2,6-substituted anthracene derivatives with symmetric planar conjugated molecular structure.This kind of anthracene derivatives are beneficial for the crystallization of organic semiconductor and hence are helpful for improving the qualities of organic semiconductor crystals.After the investigation of the properties of organic semiconductor crystals,the practical applications of organic semiconductor crystals should be taken into consideration.Patterning of organic semiconductor crystals is the prerequisite condition for achieving its applications in integrated circuit.Hence,it is necessary to study how to control the growth positions of crystals of this kind of anthracene derivatives,so as to obtain arrays of organic semiconductor crystals.Therefore,the research in this paper can mainly be divided into two parts,the investigation of the properties of organic semiconductor crystals and its controllable growth.The first is the investigation of the properties of organic semiconductor crystals.We choose 2,6-di-phenylethynyl-anthracene(DPEA)for this investigation and fabricate its crystals by physical vapor transport(PVT)method.The crystals were characterized by many methods such as optical microscopy,atomic force microscopy,scanning electron microscopy,transmission electron microscopy and X-ray diffraction.By analyzing the characterization results,we confirm that the fabricated crystals are single crystalline and obtain the molecular stacking mode as well as its lattice parameters.And the layer-by-layer growth mechanism of DPEA single crystals was also determined.For the investigation of the intrinsic properties of DPEA,we fabricate field-effect transistors based on DPEA single crystals with bottom-gate top-contact configuration by using gold-film transferring technique.The test results revealed that DPEA has good performance with the highest mobility of 4.52 cm2 V-1 s-1 and the average mobility above 2 cm2 V-1 s-1.Moreover,the device showed dramatically low contact resistance with value of 335 ? cm.The device also showed good stability.After storage in atmosphere for about one month,the performance of the device showed slight fluctuation.By studying the mobility-temperature relationship,the charge transport in DPEA single crystals can be determined to be band-like transport.By investigating the properties of organic semiconductor crystals,we master the growth method of organic semiconductor crystals.And we try to control the crystal growth based on this method.We proposed a new method for fabricating the arrays of organic semiconductor crystals.By seeding crystal nucleus in specific place via thermal evaporation in advance,organic semiconductor crystals could be controlled to deposit at corresponding place in the latter physical vapor transport process.Thus,the arrays of organic semiconductor crystals can be obtained.By optimizing the density of crystal nucleus through thermal annealing or rinsing in solvent,arrays of organic semiconductor crystals can be improved.Seeding crystal nucleus can realize the limited-area growth of organic semiconductor crystals and provide a new way for fabricating arrays of organic semiconductor crystals by PVT method.This new method can also facilitate the applications of organic semiconductor materials in organic electronics.