Study On The Controllable Preparation Of Organic Micro/Nano-crystals And Their Charge Transport Properties

Organic field-effect transistors(OFETs)have become the focus of increasing research activity in organic electronics,which are key building blocks of semiconductor devices.Among all the active materials,organic semiconductor micro/nano-crystals have the advantages of crystalline structures and no grain boundaries,offering an ideal platform for elucidating intrinsic characteristics and the influence of intermolecular interaction and molecular stacking modes on the device performance.Therefore,this study on the morphologies of organic semiconductor micro/nano-crystals not only provides great fundamental understanding but also offers effective methods in the application.However,the preparation of organic semiconductor micro/nano-crystals remains a great challenge for a long time and needs to be more deeply studied.This thesis has mainly concentrated on the controllable preparation of organic semiconductor micro/nano-crystals and the charge transport characteristics including three sections:(1)As for 2FCZ,TIPS and TrNa,organic semiconductor micro/nano-crystals with various morphologies can be obtained by varying the crystallization conditions such as the quality of solvents and the concentration.In the case of the same concentration,the ratio of good/poor solvents has a great influence on the crystal morphology.TrNa is a new kind of polycyclic aromatic hydrocarbons with superior optoelectronic properties and we thus exert great efforts on it.When the dichloromethane/ethanol ratio approaches 1:2 with the concentration of 0.5 mg/mL,the rod-like crystals are obtained,which are prone to stack.With the decreased concentration as 0.25 mg/mL,the regular rod-like crystals are prepared with good dispersion on the substrate.It is worthwhile to mention that the curved crystal is observed by further decreasing the concentration to 0.05 mg/mL.This kind of crystals has good flexibility which is different from traditional crystals with fragile characteristics.(2)The addition of different organic semiconductors into TrNa has been employed as the platform for systematically investigating the impact of organic composites on the crystalline behaviors and morphologies,which can further affect the device performance of OFETs.As for TrNa-TIPS,the introduction of TIPS can increase the π-π interaction:on one hand,it can improve the crystal morphologies while maintaining the original morphologies of the two compounds,which lead to TrNa crystals with smooth surface and TIPS crystals with regular rhombus;on the other hand,it can greatly enhance the electrical properties(μTrNa=0.96 cm2/V·s,|μTIPS=1.45 cm2/V·s).In the case of TrNaTCNQ,TrNa serves as acceptor and TCNQ acts as electron donor,which can result in co-crystals with the donor-acceptor interaction.The hexagonal TrNa-TCNQ co-crystals has been obtained for the first time.(3)As an extrodinary optoelectronic material,BSBCz has great potential for achieving organic electrically-pumped lasing.In order to expand its application in OFETs,BSBCz crystals are obtained by means of microspacing in-air sublimation growth with simple equipment and fast crystalline time.Meanwhile,the crystalline process and the morphological modulation have been studied in details.The process corresponds to the fast solvent evaporation at the elevated temperature,achieving crystals in the bottom substrate,which greatly differs from microspacing in-air sublimation growth previously reported.Two typical crystal morphologies including nanowire and nanobelt have been obtained for the first time by changing substrate temperature and heating time.Under this circumstance,BSBCz nanobelt crystals have ambipolar characteristics.