【作者】 姜辉；

【导师】 杨贤金； 胡文平；

【作者基本信息】 天津大学 ， 材料学， 2008， 博士

【摘要】 有机单晶微纳器件的研究对于探索材料电子传输的本征特性具有十分重要的意义。我们在制备高性能有机单晶场效应晶体管的同时,分析有机单晶的分子结构、生长方向、堆积形式等有助于我们认识电子传输与分子结构之间的关系,理解电子沿有机晶体各个方向传输的本征特性,并获得具有高性能参数的理想分子形态,将提高有机功能分子可控合成的成功概率。作为研究最为广泛的杂环系统,四硫富瓦烯（TTF）以及衍生物以其优异的物理与化学性质受到广泛研究。本论文主要以TTF以及衍生物为代表研究其有机单晶场效应晶体管和光晶体管,主要研究内容如下:（1） TTF单晶存在两种相态,采用不同溶剂分别可控合成两种相态的TTF单晶。实验中采用正庚烷溶剂能够可控生成TTF的一维α相,而氯苯溶剂能够可控生成TTF的一维β相,通过控制单晶生长的过程参数能控制单晶尺寸的大小;采用溶液法原位制备TTF单晶场效应晶体管。对大量器件数据总结后发现,不同相的迁移率有所不同,α相的最大迁移率能达到1.2cm2V^-1s^-1,而β相的最大迁移率仅为0.23 cm2V^-1s^-1;将TTF分子之间的电荷传输过程模拟为一种Brownian迁移过程,理论结果显示与实验结果完全吻合。（2）合成了TTF的一种衍生物TCTT-TTF,主要在TTF两边四个不稳定位置上引入四个氰乙硫基。采用溶液法自组装生成各种形貌与尺寸的TCTT-TTF单晶;对比TCTT-TTF与α相TTF的电化学稳定性、热稳定性、真空稳定性等,分析两种晶体的分子结构与堆积。结果表明,TCTT-TTF的稳定性远远好于α相TTF;采用溶液法原位制备TCTT-TTF单晶场效应晶体管,其中绝缘层为聚乙烯醇（PVA）与十八烷基三氯硅烷（OTS）双层修饰;采用三氯甲烷溶剂获得器件的迁移率、开关比和阈值电压分别为0.01cm2V^-1s^-1、1.1×10³和26.7V。（3）β相TTF单晶与TCNQ单晶对光都具有响应性。其中β相TTF单晶对光的响应时间超过60s,光开关比较低;而TCNQ单晶对光的响应时间则低于0.5s,光开关比超过100;栅压的引入对两种晶体的响应度无影响,只是改变光开关比;对比β相TTF与TCNQ晶体结构发现,分子间π···π作用,包括“边对边”、“面对面”的堆积越好,越有助于提高光生载流子的传输速率,同时提高电子与空穴重新结合的几率与速率;而相对松散的堆积结构使得光生载流子的传输速率降低,同时也降低了电子与空穴重新结合的几率与速率,从而表现出强烈的残留电导率,并且无法通过栅压的调节而获得改善;TCNQ单晶光晶体管显示出良好的光导作用,具有很好的应用前景。更多还原

【Abstract】 It’s very important to develop micro- and nano-sized organic single crystallinedevices for investigating the intrinsic transport property of organic semiconductor. Wehave fabricated high performance organic single crystalline field-effect transistors andanalyzed molecular structure, growth direction and molecular packing of organicsingle crystals, which will help us understand the relationship between molecularstructure and transport properties and the transport anisotropy of organic singlecrystals, and obtain ideal molecular configurations with high device performance tocontrollably synthesize organic functional molecules.As the widely studied heterocyclic system, TTF and its derivatives have beenapplied into various fields because of outstanding physical and chemical properties.This paper has studied organic single crystalline field-effect transistor andphototransistor of TTF and its derivatives, and the main results are presented asfollows:（1） The crystals of TTF existed in two polymorphic modifications, and we haveadopted different solvents to grow TTF single crystals with different phases. Inour experiments, one-dimensional pureαphase TTF single crystals could becontrollably obtained by the selection of n-heptane while one-dimensional pureβphase could be provided by chlorobenzene. The size of these crystals could beaccurately controlled by the parameters of crystal growth process. TTF singlecrystalline field-effect transistors with two phases have been in situ fabricated bydrop cast. The mobilities of different phases were different. The maximumfield-effect mobility ofαphase was near 1.20 cm2V^-1s^-1 whileβphase showedthe maximum mobility only about 0.23 cm2V^-1s^-1. We modeled the chargetransport of TTF molecule as a Brownian motion process, and the results oftheoretical calculations have been highly accorded with our experimental results.（2） One of TTF derivatives, TCTT-TTF have been synthesized based on theintroduction of four groups of cyanoethylthio at the instable positions of TTF.Single crystals of TCTT-TTF with various patterns and dimensions could beobtained by solution self-assembly. The comparisons of electrochemical stability,thermal stability and vacuum stability combined with the analysis of molecularstructure and packing between TCTT-TTF and TTF have showed that the stabilityof TCTT-TTF would be greater than that of TTF. TCTT-TTF single crystalline field-effect transistors have been in situ fabricated by the drop cast and theinsulators have been modified by the combination of polyvinyl alcohol （PVA） andoctadecyltrichlorosilane （OTS）. The field-effect mobility, on/off ratio andthreshold voltage of the device by the selection of chloroform would be 0.01cm²V^-1s^-1, 1.1×10³ and 26.7 V, respectively.3) Single crystal ofβphase TTF and TCNQ have been responding to the lightirradiation. The response time ofβphase TTF single crystal would exceed 60 sand on/off ratio between dark and light irradiation would be very low while theresponse time of TCNQ single crystal would be below 0.5 s and on/off ratiowould be greater than 100. The introduction of gate voltage would have no effectin the responsibility of the two kinds of crystals and just modify on/off ratio.Comparison of crystalline structure and packing betweenβphase TTF and TCNQhave showed that more perfect packing ofπ···πinteraction between molecules,including the packing of“side-by-side”and“face-to-face”, the more rapid thetransfer speed of the photo-excited carriers would be, at the same time the chanceand speed of recombination of electrons and holes would be further enhanced.Relatively loose packing would result in the low speed of the transfer of thephoto-excited carriers and reduction of the chance and speed of recombination ofelectrons and holes, which would show very high persistent conductivity andcould not be improved by the adjustment of gate voltage. TCNQ single crystallinephototransistor showed good function of light guide and great potentials ofapplication.更多还原