Large-Scale Fabrication Of High-Quality Organic Semiconductor Single Crystal Films And Their Application In Organic Field-Effect Transistors

Organic single crystal films(OSCFs)with long-range ordered molecular stacking and low defect density are widely used in various electronic and optoelectronic devices.However,present organic single crystal growth methods have difficulty assuring crystal orientation homogeneity and controlling molecule stacking structure,it is still challenging to achieve large-area organic single crystal films with controlled structure.Aim at the above problems,my research focused on the following two aspects:1.Fabrication of Large-area C8-BTBT Single-Crystal Films via an Orientation Filter Funnel for Organic Field-Effect TransistorsIn this work,we advance a new strategy to fabricate large-area OSCFs with wellaligned,singly orientated crystals based on scalable blade-coating method through an"orientation filter funnel" concept.A V-shaped solvent-wetting region is used as a funnel to screen out the seed crystals with the unitary crystallization orientation,followed by adjacent solvent-wetting triangle region for their further propagation.After that,these singly orientated seed crystals enter into a designed growth control region,the alternating wetting/dewetting lines could ensure these crystals uniformly grow along the same crystallographic orientation,eventually forming the orderly 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene(C8-BTBT)OSCF(1.5 × 1.5 cm2).The obtained C8-BTBT OSCFs have an ultralow trap density of 7.3 × 109 cm-3.C8-BTBT OSCFbased 7×8 OFET arrays have an average mobility of 8.30 cm2 V-1 s-1,which is 4.5 times higher than that of the polycrystalline C8-BTBT array(1.85 cm2 V-1 s-1)without orientation filter funnel concept.In addition,the C8-BTBT OSCF exhibits unprecedented device-to-device uniformity with narrow distribution of mobilities and Vth.Significantly,the CV(the ratio of the standard deviation to the average),of C8BTBT OSCF mobility is only 9.8%.It is much lower than that of organic semiconductor films prepared with other solution printing techniques(12.3-28.1%)and low-temperature polysilicon(LTPS)(11.8-17.8%).Further,we used the C8-BTBT OSCF to construct three universal logic gates,including inverter,NOR,and NAND.These findings offer insights into the development of large-area OSCFs and provide a platform for constructing high-performance organic single-crystal electronics for future applications.2.A Method toward Tuning Molecular Packing in C8-BTBT Single-Crystal Films for High-Performance Organic Field-Effect TransistorsIn this work,we achieve the rapid fabrication of C8-BTBT single crystal films with modulation of molecular stacking structure by adding the nonionic surfactant Triton X100 into the small molecule semiconductor C8-BTBT solution.Due to the strong interaction between Triton X-100 and C8-BTBT molecules,the solute transport rate during the coating process is enhanced,which in turn accelerates the crystal growth rate for rapid fabrication of high-quality C8-BTBT single-crystal films.The existence of strong interactions between Triton X-100 and C8-BTBT molecules is demonstrated by UV-vis absorption,differential calorimetric scanning,and molecular dynamics simulations.And the lattice distortion of C8-BTBT is also found in the X-ray diffraction,with a tighter π-π stacking along the(010)plane direction,which facilitates the carrier transport.We obtain the optimal blade-coating speed of 1.2 mm s-1 and Triton X-100 concentration of 1.25 mg mL-1 from the controlled experiments of film morphology and device performance.OFETs based on the C8-BTBT single-crystal films exhibit excellent device performance with a maximum hole mobility above 10 cm2 V-1 s-1,which is 3 times higher than that of the device without the addition of Triton X-100 molecules.NAND logic gate circuits are successfully prepared,which exhibits ideal voltage transfer characteristics.This work provides a new approach to tune the molecular stacking structure in organic single-crystal films for high-performance printed electronics.