In Situ Crystallization Process And Growth Method Of Organic Photoelectric Functional Crystals

Organic functional materials have attracted significant interest because of their key roles in diverse of electronic,optical,and optoelectronic applications.The traditional techniques for the incorporation of organic materials in most of the applications prefer a morphology of thin films,because of their large area,light weight,flexibility,and reproducibility of characteristics of individual elements.However,extrinsic structural defects in amorphous or polycrystalline films impede the photon,electron,and/or exciton manipulation and migration inside the semiconducting layers.Single crystals of organic photoelectric functional materials possess overwhelming superiority over amorphous or polycrystalline counterparts,due to the molecular long-range ordered,absence of grain boundaries and molecular disorder.To this extent,to grow high quality organic crystals is significant for the investigation of the intrinsic properties of organic semiconductors.How to provide an ideal growth condition for crystal growth by controlling the external environment is the primary issue for organic crystal growth.The integration of organic crystals on substrates is the basis for nearly all the organic optoelectronic devices.The most developed growth methods of organic crystals are based on vapor and solution processing techniques.However,traditional growth of organic single crystals is limited by low solubility from solutions,or complexity from physical vapor deposition.The preponderant value of organic single crystal is still confined to be the ideal platforms to investigate the intrinsic structure-performance relationships but not for large scalereal applications.Therefore,it is important to develop an efficient and simple method to evaluate crystalline materials for their performances in devices.Secondly,understanding the crystallization process and influencing factors of the crystal is also important.Knowing well the characteristics of crystal growth can better guide the control of crystal growth.Crystal formation from solution or vapor phase can usually be directly observed.However,for solid state crystallization,imaging of the growth process is difficult.The nucleation and growth in these transformations usually occurs in confined environments,and the interfaces of the newly formed crystals are buried in the solid body of the material,making the direct observation infeasible.Many advanced technologies have been employed to monitor the crystallization process in real time and under realistic growth conditions.These significant studies of in situ imaging of crystal formation rely heavily on extremely hightech instrumentation,nevertheless,they are still quite rare for solid state crystallization because of the ambiguous interface in the coexistence of amorphous/crystalline regions.An alternative approach has been to employ micro-colloidal particles in suspensions as model systems to study phase transitions and nucleation.However,this method is simulated and not real.Based on the above mentioned considerations,this thesis is focused on the in situ observation of the crystallization process and crystal growth mothed of organic photoelectric functional crystals.The main contents are as follows:1.In situ microscopic observation of the crystallization properties process of molecular microparticles by fluorescence switching.A novel kind of compounds with morphology-dependent fluorescence was utilized to distinguish the interfaces between the crystalline and amorphous phase by fluorescence color,and to accomplish the imaging on an optical microscopy.The crystallization of an amorphous microparticle was shown to nucleate at its center.However,the growth was confined to the inner part of perfectly spherical microparticles,ending with a core-shell structure.Defects of the surface prior to crystallization can lead to a complete conversion from an amorphous sphere to a ribbon-like crystal.Profiting from the response of the self-fluorescence,the appearance and the interface evolution of the forming crystalline phase inside the particle can be clearly observed.The study presents a realistic picture of the microscopic kinetics of a solid-solid transition,which we believe will deepen the understanding of many solid-state crystallization processes that occur spontaneously in atmosphere or under external stimuli.2.Microspacing in-air sublimation growth of organic crystals.A substantially new method to directly grow organic single crystals on substrate by microspacing in-air sublimation was reported.The method represents an advance on both growth mechanism and implementation techniques.The synergy effect between the microspacing and the temperature distribution induced an unprecedented vapor transport regime and crystallization mechanism.A vapor-to-melt-to-crystal process was revealed via in situ observation.The method,by employing 10 kinds of organic crystals,including different semiconductors and a pharmaceutical crystal,that were successfully grown with high crystallinity proved a broad generality to various materials.The method,totally being implemented at ambient conditions,requiring neither vacuum systems,nor inert gases,nor even a growth chamber,possesses advantages in many aspects such as growth time,materials utilization ratio,applicability for real time observation,etc.This effective organic crystal growth technique can be affordable and handled for almost every lab,which may bring about revolutions in future research and application of organic crystals.3.Cocrystal growth and morphology control of organic semiconductors by microspacing in-air sublimation.We employed our recently developed micro-spacing in-air sublimation to grow co-crystals of a series of polycyclic aromatic hydrocarbon(PAH)-1,2,4,5-tetracyanobenzene(TCNB)complexes.Moreover,the method realized morphology control over the cocrystals of different charge-transfer complexes.By precise manipulation of the starting materials(e.g.,being thoroughly mixed or separated located on the source substrate)and growth temperature,the cocrystals grown on the upper substrate can be endowed with one-dimensional(1D)and two-dimensional(2D)morphology on demand.