Aligned And Patterned Assembly Of Organic Semiconductor Micro-/nanocrystals And Their Applications In Field-effect Transistors

Single-crystalline organic micro/nanocrystals(SOMNs),compared with their amorphous and polycrystalline counterparts,are ideal material for both charge transport study in organic materials and fabrication of high-performing optoelectronic devices,as they have long-range order,fewer structure defects and higher mobility.Recently,SOMNs have aroused increasing interest due to their unique properties and prospective applications in high-performance and low-cost flexible FETs.Although,charge carrier ? of SOMNs makes these materials excellent candidates to future electronic circuits,they are difficult to scale-up for technological applications,because the SOMNs can not cover the entire substrate and the growth location and orientation is random in nature.To overcome these problems,this thesis is mainly focused on aligned and patterned assembly of SOMNs and their applications in high-performance,large-scale,flexible field-effect transistors.These results are summarized as follows:1.We have demonstrated a highly efficient yet simple method that combines the technique of photolithography and spin-coating to produce organic nanowire(NW)arrays at designated locations with high-precision and high-efficiency.During the process,the 9,10-bis(phenylethynyl)anthracene(BPEA)solution tended to converge to the sides of the prepattemed photoresist.After solvent evaporation,the growth,alignment,and precisely patterning of NWs are completed simultaneously within 1 min on the entire substrate.Various desired complex patterns of single-crystal BPEA NW arrays were successfully obtained.High-performance NW array-based FETs were constructed with mobilities up to 3.5 cm2 V-1 s-1(average mobility of ?2.52 cm2 V-1 s-1).This strategy offers a means to generate patterned OSMNs NW arrays in any desired directions,which can perfectly repeat the pattern shapes of the photoresist.The efficient patterned growth of wafer-scale organic semiconductor arrays with high resolution at desired locations opens up the opportunities for future high-performance,low-cost organic electronic and optoelectronic devices.2.We put forward a photolithography-assisted dip-coating technique to grow organic single-crystalline NW arrays.And wafer-scale and precisely positioned uniform organic NW arrays can be generated.The FETs based on 6,13-dichloropentacene(DPA)NW arrays exhibit an average and the maximum ? of 30.3 cm2 V-1 s-1 and 39.36 cm2 V-1 s-1(the highest value obtained for organic semiconductors)with highly uniform mobility(standard deviation of 5.36 cm2 V-1 s-1).Simultaneously,single-crystalline NW FETs arrays can be transferred to flexible substrate and curved surface with high ?(?11.05 cm2 V-1 s-1),forming flexible and conformal electronics with extreme bending stability.All these results indicate the great potential of the as-prepared single-crystalline NWs in the application of large-area high-performance flexible devices.3.We demonstrate a highly efficient method that utilizes photolithography to create patterned-wettable/unwettable channels to simultaneously produce alignment and patterning of organic semiconductor crystals(OSCs).Using this strategy,the positions and shapes of the patterned OSCs arrays can be readily tuned by photolithography with high precision.By combining photolithography aligning system,this method enables fabrication of patterned OSC arrays onto pre-patterned transistor source-drain electrodes to create high-integration FET matrix,while effectively reducing gate leakage current and crosstalk among devices.The FET matrix contains 117(9 × 13)devices in the area of one square millimeter,which represents the highest degree of integration in organic electronic devices.The FETs possess high performance with mobility as high as 9.78 cm2 V-1 s-1(average mobility of up to ? 8.68 cm2 V-1 s-1),which is remarkably higher than that of previously reported aligned crystals.Our work provides an opportunity to push forward organic semiconductors into high-integration applications.4.We developed a grating-assisted physical vapor deposition and a contact printing method for the growth of aligned copper phthalocyanine(CuPc)NW arrays on flexible substrates.Then we used a transfer printing method to fabricate NW array based FETs on flexible substrates.The impact of substrate thickness,as well as bending direction on the device stability,was further investigated.It was found that the FETs fabricated on the thin PDMS substrate exhibited excellent bending stability.More interestingly,the thin exible devices could be attached to the palm of a human hand,opening up the opportunities for a wide range of electronic applications such as electronic skin.5.We have demonstrated several simple yet efficient methods to fabricate NW-array-based FETs on the sellotape substrate.Organic NW devices fabricated on the sellotape substrate exhibit several key features,including extreme high bending stability while being curved into a radius of 3 mm,fine wearing stability for multitimes wear,and ability to construct 3D multifunctional circuitry for up integration.More than 60%CuPc ONWFETs possess a high mobility of over 1.0 cm2 V-1 s-1 with average mobility of ? 1.02 cm2 V-1 s-1,which is the best reported values at flexible substrates.The fabrication method can be readily extended to a wide range of organic nanostructures as well as various complex electronic devices,which may find important and innovative applications in future flexible,wearable,and 3D organic electronics.