Large-area Growth Of Organic Single-crystalline Thin Films And Their Application In Field-effect Transistors

In recent years,small-molecule organic semiconductor single crystals have attracted much attention due to their excellent optoelectronic properties and compatibility with plastic substrates.Despite of all these advantages,the scale-up of organic single crystals for practical applications is still difficult because the growth orientation and location of organic single crystals are usually stochastic in nature.In this thesis,large-area organic semiconductor single-crystalline thin films have been achieved via simple solution methods.We further investigate the relationship between growth conditions and charge transport properties of single-crystalline thin films.At last,the high-mobility and flexible field-effect transistors(FETs)based on organic semiconductor single-crystalline thin films are constructed.These results are summarized as follows:1.Controlled growth of large-area aligned single-crystalline nanoribbon thin films for organic field-effect transistorsWe have described a solution-processed dip-coating technique to grow large-area aligned 9,10-bis(phenylethynyl)anthracene(BPEA)and 6,13-bis(triisopropylsilylethynyl)pentacene(TIPS-PEN)single-crystalline nanoribbon thin films.Our method is scalable up to a 5 × 10 cm2 wafer substrate with around 60%of the wafer surface covered by aligned crystals.The quality of crystals can be easily controlled by tuning the dip-coating speed.Furthermore,OFETs based on well-aligned BPEA and TIPS-PEN single-crystalline nanoribbon thin films are constructed.By optimizing channel lengths as well as using appropriate metals electrodes,the BPEA and TIPS-PEN based OFETs show hole mobility exceeding 2 cm2 V-1 s-1(average mobility 1.2 cm2 V-1 s-1)and 3 cm2 V-1 s-1(average mobility 2.0 cm2 V-1 s-1),respectively.Both of them have high on/off ratio(Ion/Ioff)>109 and perfect stability.The performance can well satisfy the requirements for light-emitting diodes(LEDs)driving.Hence,our method facilitates the fabrication of large-area aligned organic single-crystalline thin film for high-performance and large-area device applications.2.Fabrication of large-area two-dimensional organic single-crystalline thin films and their application in organic field-effect transistorsWe develop an efficient approach based on drag coating of a blend of organic semiconductor,2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene(dif-TES-ADT)and insulating polymers to grow large-area,two-dimensional(2D)dif-TES-ADT single-crystalline film on the water surface.We demonstrated that several growth parameters(i.e.,molecular weight(Mw)of the PS,semiconductor/binder polymer ratio,dragging speed and solvent composition)have significant influences on the film morphology,microstructures,crystal qualities,and eventually the charge transport properties.In doing so,we demonstrate FETs with carrier mobility as high as 24 cm2 V-1 s-1,Ion/Ioff ratio exceeding 107,surpassing the single-crystal counterparts.In addition,this film can be transferred onto flexible substrate to fabricate high-performance flexible FETs with excellent bending stability(bending radius down to 3 mm).Our methodology provides a convenient route to assemble large-scale and high-quality 2D organic single-crystalline film with novel structure and function for their applications in flexible-and opto-electronics..3.Fabrication of aligned single-crystalline nanoribbon thin films based field-effect transistors on flexible substrateA simple yet efficient transfer printing method is utilized to achieve aligned single-crystalline nanoribbon thin films based FETs on flexible substrates.By using an insulating polymer layer as a supporting layer,aligned single crystalline nanoribbon films with source and drain electrodes can be readily transferred to diverse conventional or non-conventional substrates that are not easily accessible before with a high transfer yield of about 100%.The flexible FET devices demonstrate a high mobility up to 4.5 cm2 V-1 s-1,average mobility 2 cm2 V-1 s-1 with a high Ion/Ioff>105,and excellent bend stability with bending radius down to 0.5 mm and fold 1000 times.Notably,these devices exhibit performance comparable to the device counterparts fabricated by conventional methods,demonstrating the high reliability,robustness,and efficiency of the transfer printing method.It is expected that the transfer printing method will have important applications in future flexible organic electronics.