| Organic semiconductor single crystals have the characteristics of long-range order,no grain boundaries,and low density of defect states,which are ideal tools for studying the structure-property relationships of organic semiconductors and are important materials to construct high-performance optoelectronic devices.Compared with three-dimensional bulk organic single crystals,low-dimensional organic semiconductor single crystals(including 1D organic single crystals and 2D organic single crystals)also have unique structural advantages such as large surf ace-to-volume ratio and molecular-level thickness.These structural advantages give advantages such as high sensitivity to external stimuli and low contact resistance in devices,which are expected to play indispensable roles in future flexible electronic circuits.However,the preparation of low-dimensional organic semiconductor single crystals requires to strictly control the growth conditions such as nucleation density,growth orientation,and the existing preparation methods based on three-dimensional bulk organic single crystals are difficult to meet these demands.The challenge of preparation hindered the investigation of their optoelectronic properties and limited their application in organic optoelectronic devices and circuits.Our studies are carried out in response to these challenges:(1)A thermally-assisted self-assembly(TASA)strategy is proposed to prepare large-area uniaxial organic single-crystalline microribbon arrays(OSCMAs).The TASA strategy achieves synergistic control of nucleation and growth during crystallization.It exhibited a self-adaptive characteristic with large temperatures(40 ??100 ?)and concentrations(2 mg mL-1?7 mg mL-1)tolerance.Using this strategy,centimeter-scale OSCMAs of 6,13-Bis(triisopropylsilylethynyl)pentacene(TIPS-pentacene)were prepared,and their phototransistors(OPT)exhibit an unprecedented photosensitivity of 1.36 × 108.The TASA strategy is simple and efficient,it provides a new method for preparing large-area OSCMAs.(2)A surfactant-assisted self-assembly(SAS)strategy is developed to prepare large-area 2D organic single crystals(2DOSCs).The SAS strategy enhances the inward Marangoni flow and suppresses the "coffee ring effect".The strategy can be used to grow 2DOSCs of different organic semiconductors.A large-area 2DOSC of 2,6-bis(4-hexylphenyl)anthracene(C6-DPA)was successfully prepared using the SAS strategy and the average mobility of OFETs based on C6-DPA 2DOSCs by the SAS strategy was as high as 3.03 cm2 v-1 s-1.The SAS strategy provides an efficient method for the preparation of large-area 2DOSCs and lays a foundation to investigate their charge transport properties.(3)1D/2D organic single crystal heterojunctions are prepared by using 2DOSCs as dopants to achieve controllable and efficient doping of organic semiconductors.The 2DOSCs can not only closely adhere to the host material to achieve efficient doping but also its controllable thickness at molecular level ensures accurate doping of the host material at the molecular level.As a result,compared with the pristine materials,the average mobility of OFETs based on 1D/2D organic single crystal heterojunctions increased from 1.31 cm2 v-1 s-1 to 4.71 cm2 v-1 s-1,corresponding to an increase of 260%.Moreover,high on/off ratios up to 108were retained.The 1D/2D organic single crystal heterojunction proposed in this research is a new structure to achieve controlled and efficient doping and provides a useful example for the realization of high-performance OFETs and other devices through doping.(4)A in-situ heteroepitaxy method for the preparation of 2DOSC p-n heterojunctions is proposed and their charge transport properties are investigated.Liquid substrate is used to eliminates the universal "coffee ring effect" of solid substrates.By heteroepitaxy growth of 2DOSC on the liquid substrates,large-area heterojunctions are obtained successfully.One key advantage of the in-situ heteroepitaxy strategy is that it avoids interface contamination of the layer-by-layer stacking method and obtains a clean heterojunction interface.Ambipolar OFET based on p-n heterojunction exhibited electron and hole mobility as high as 0.95 cm2 v-1 s-1 and 0.98 cm2 v-1 s-1,respectively,which are the highest values among organic single crystal double-channel OFETs measured in ambient air.The excellent charge transport characteristics indicate the heterojunctions obtained by the in-situ heteroepitaxy method has high quality.The method developed here avoids the interface contamination problems of the traditional layer-by-layer stacking method and provides a new way to prepare high-quality heterojunctions. |
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