Study Of Solution Growth And Other Related Aspects Of Organic Semiconductor Single Crystals

Field-effect transistors made of organic single crystals are attractive candidates for electronic applications such as active matrix displays, sensor arrays, organic laser and integrated circuit. The intrinsic electronic transport properties of organic semiconductor are the foundation of theoretical simulation for organic thin film transistors (OTFTs) and the field-effect experiment is a very important method to study the intrinsic electronic transport properties of organic semiconductor. Compared with organic films, organic single crystals are free from structure disorder and grain boundary. So the research on the organic single crystal transistors (OSCTs) has attracted much attention in recent years.Currently, vapor-phase growth methods, such as the physical vapor transport (PVT) are the main mean of producing such organic single crystals. The solution method is an old but effective method for crystal growth. It may have advantages for industrial applications, since it does not require any large apparatus (such as a vacuum apparatus), it allows a solution to be dropped or applied directly onto substrates, and it is expected to allow the crystals to be produced in a lower-temperature region as compared to vapor-phase growth. Large-size and high-quality anthracene single crystals have been grown by a solution technique in this paper. The size of crystals reaches to 2.2 cm and the crystals with rhombic plane have been obtained for the first time. FTIR and Raman analysis indicate that the crystals did not incorporate the solvent at the detection level. XRD analysis indicates that the anthracene single crystals have good quality. The morphology of surface and transect of anthracene single crystals was observed by optical microscope, atomic force microscope (AFM), and scanning electron microscope (SEM). Anthracene monolayers and the array of large straight steps were observed on the surface of anthracene single crystals. Layer-like structure was also observed in the interior of single crystals. All results indicate that the growth mechanism of anthracene single crystals is a two-dimensional nucleation–elementary steps–large straight steps–layer-by-layer periods growth.The anthracene/anthracquinone mixed crystals also have been grown by a solution technique and the fluorescence spectrum have been studied.Large-size and high-quality rubrene single crystals have been grown by a solution technique. The biggest crystal has 4 mm dimension. Fourier transform infrared spectroscopy and Raman spectroscopy both indicate that the crystals obtained are pure rubrene and did not incorporate the solvent at the detection level. The morphology of surface and transect of the rubrene single crystals was observed by optical microscope, atomic force microscope and scanning electron microscope. Three-dimensional nucleation happened on the surface of single crystals. The array of small and large straight steps was observed on the surface of the rubrene single crystals. Layer-like structure was also observed on the cross-section of single crystals. All results indicate that each large step is most probably formed from the piling of small steps and the growth mechanism of rubrene crystals grown from solution is probably a three-dimensional nucleation–layer-by-layer periods growth.In a word, three different crystals have been grown by solution technique. The effect factors discussed, growth conditions optimized. We also have concluded two the growth mechanisms for anthracene and rubrene respectively. Certainly, these results are very promising for the study of the growth mechanisms of other organic single crystals.