有机半导体薄膜的光学和电学性质研究

采用真空热蒸镀技术制备了NPB有机半导体薄膜和单层夹心结构器件,通过透射谱测量研究了薄膜的光学能隙、折射率和消光系数等光学性质,结果表明有机半导体薄膜具有直接带隙半导体的光学性质,并且其折射率色散性质遵循单振子模型.另外,通过分析器件的电流-电压特性研究了薄膜的电导率、载流子迁移率和载流子浓度等电学性质.这些实验结果对于有机光电子器件的结构设计具有一定的参考价值.     

基于金属电极和有机半导体层的制备工艺对有机薄膜晶体管性能的研究

基于聚合物绝缘材料和半导体材料,采用溶液法旋涂工艺制作了有机薄膜晶体管(OTFT),通过不同方法制备有机半导体层、栅极和漏极,以提高有机薄膜晶体管的器件性能.结果表明,有机半导体层是否图形化以及不同金属电极的制备工艺对器件的接触电阻影响明显.有机半导体层图形化后,器件的开关比有较大的提升.采用lift-off工艺,先在聚合物绝缘层材料上对光刻胶图形化,然后利用真空蒸镀法将金属电极蒸镀到绝缘层材料上,最后将器件浸泡在70℃的NMP溶液中约30 min,接触电阻约为4.8×107 Ω;采用湿刻工艺对蒸镀在绝缘层材料上的金属电极进行处理,接触电阻有明显的下降,约为3.6×106 Ω.     

高性能顶栅结构有机薄膜晶体管

采用六联苯(p-6P)和氧钒酞菁(VOPc)作为有源层材料,利用弱外延生长技术制备有机薄膜晶体管(OTFT)。在相同的工艺条件下制备了顶栅结构(top-gate)和底栅结构(bottom-gate)两种器件构型,发现两种不同结构的OTFT器件特性存在较大的差异,top-gate OTFT的迁移率比bottom-gate OTFT高很多。在顶栅结构的器件构型中获得了较高的器件特性参数,迁移率达到1.6cm2/V.s。研究了弱外延生长技术应用在两种不同器件构型中的差异,并解释了顶栅结构OTFT迁移率较高的原因。     

高性能有机薄膜晶体管(OTFT)制备及其导电机制

详细介绍了在SiO2和高kHfO2介质层上制备并五苯薄膜晶体管方面的研究,特别是利用原子力显微技术(AFM)和静电力显微技术(EFM)研究了并五苯分子初始生长模式,揭示了衬底形貌、表面化学性能(包括化学清洗和聚合物层修饰)对有机半导体成膜结构和薄膜场效应晶体管性能之间的关联,包括晶体管迁移率、开关比和阈值电压等;针对并五苯初始生长成核模式的差异,分析了不同岛(畴)间畴边界对载流子在有机薄膜内输运的影响,有助于理解有机半导体薄膜导电机理。通过优化和控制介电层和有机半导体薄膜层的界面化学性质,在SiO2介质层上成功制备出迁移率为1.0cm2/V.s、开关电流比达到106的OTFT器件;在高kHfO2介质层上获得的OTFT器件的工作电压在-5V以下,开关电流比达到105,载流子迁移率为0.6cm2/V.s;器件性能指标已经达到目前国际上文献报道的最好水平。     

有机半导体在非对称金-石墨烯电极上的取向生长

为了实现在微尺度范围内有机半导体的取向生长,提出了一种基于不对称金-石墨烯电极的底接触有机薄膜晶体管器件结构。半导体前驱体溶液在不同衬底上表现出的不同接触角将打破液体/空气界面处的表面张力与表面能的总体平衡,形成马兰戈尼流并促使溶液在低润湿性的石墨烯电极表面的接触线快速后退。实验结果表明,基于这种不对称电极制备的底接触有机薄膜晶体管(OTFT)阵列的平均迁移率显著提升,达到常规对称结构器件的2倍,同时器件迁移率的相对标准差从53%下降到33%。该不对称器件结构实现了半导体薄膜在器件沟道处的取向生长,从而提高了器件迁移率与均匀性。     

8-羟基喹啉铝作为修饰层对C60有机场效应管性能影响的研究

采用真空蒸镀技术制备了以喹啉铝(tris(8-hydroxyquinoline) aluminum, Alq3)作为修饰层的C60有机场效应管器件,并研究了修饰层的厚度对于器件性能的影响。实验表明,随着Alq3修饰层厚度的增加,器件的性能参数得到改进。当Alq3修饰层厚度为10nm时,器件场效应的迁移率达到最大值,为1.2810-2cm2/Vs,阈值电压也下降到了10V。分析了缓冲层使器件性能提高的主要原因可能有两个：一个是可以阻止金属原子扩散进入C60有机层,另一个是使Al/C60界面间的沟道电阻降低。     

易于集成的有机薄膜场效应晶体管的制备

用有机半导体并五苯作为有源层,聚四氟乙烯作为绝缘层,采用全蒸镀方式在真空室一次性制备了正装结构的有机薄膜场效应晶体管(OTFT)。薄的有机绝缘层使得器件工作在低电压下,有机薄膜场效应晶体管易于与显示像素(有机发光二极管(OLED))集成在同一个透明的刚性或者柔性衬底上。研究了有机薄膜场效应晶体管的源漏接触电阻和沟道电阻对器件性能的影响,结果表明接触电阻是影响器件性能的主要因素。在透明的玻璃衬底上实现了有机薄膜场效应晶体管对同一衬底上100μm×200μm红色有机发光二极管的驱动。     

纳米结构C_(60)薄膜对TiOPc电荷分离的增强作用

研究了具有纳米结构的C60层对TiOPc电荷分离的影响。以ITO为基底,真空蒸镀TiOPc薄膜,再以真空蒸镀和电泳法分别制备C60薄膜,通过扫描电镜(SEM)观察到电泳法制备的C60电荷分离层表面具有约200μm的微结构。实验表明:TiOPc/C60器件在近红外区间的光电响应曲线与TiOPc的吸收光谱曲线趋向一致,且光伏响应随功率增加呈线性增强;具有纳米结构C60电荷分离界面的器件光电响应比具有平整C60界面的器件强60%左右,其原因在于作为电荷分离区域的TiOPc和纳米结构C60层接触的面积更大,提高了电荷分离的效率。     

高性能有机薄膜晶体管（OTFT）制备及其导电机制

详细介绍了在SiO2和高kHfO2介质层上制备并五苯薄膜晶体管方面的研究,特别是利用原子力显微技术（AFM）和静电力显微技术（EFM）研究了并五苯分子初始生长模式,揭示了衬底形貌、表面化学性能（包括化学清洗和聚合物层修饰）对有机半导体成膜结构和薄膜场效应晶体管性能之间的关联,包括晶体管迁移率、开关比和阈值电压等;针对并五苯初始生长成核模式的差异,分析了不同岛（畴）间畴边界对载流子在有机薄膜内输运的影响,有助于理解有机半导体薄膜导电机理。通过优化和控制介电层和有机半导体薄膜层的界面化学性质,在SiO2介质层上成功制备出迁移率为1.0cm^2/V.s、开关电流比达到10^6的OTFT器件;在高kHfO2介质层上获得的OTFT器件的工作电压在-5V以下,开关电流比达到10^5,载流子迁移率为0.6cm^2/V.s;器件性能指标已经达到目前国际上文献报道的最好水平。     

Se薄膜封装层对OLED器件寿命的影响

对于绿光OLED多层器件,在高真空条件下,利用真空蒸镀的方法,在各功能层蒸镀完成后,又在阴极的外面蒸镀了一层硒薄膜封装层,然后再按一般方法进行封装.对比了正常封装与增加Se薄膜封装层后器件的性能,对比实验中封装过程都未加干燥剂.研究发现未加Se薄膜封装层器件的半衰期为2 880 h,增加Se薄膜封装层器件的半衰期接近4 000 h,Se薄膜封装层的增加将器件的寿命延长了1.4倍;研究还发现Se薄膜封装层基本不影响器件的电流-电压特性、色坐标等光电性能.     

Organic thin-film transistors with bilayer of rubbed and evaporated hydrocarbon-based acene as active layer

We have investigated organic thin-film transistors (OTFTs) with a bilayer of rubbed and evaporated hydrocarbon-based acene 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) as an active layer. Using a rubbing process after spin-coating the C8-BTBT, crystallinity of the C8-BTBT thin film was improved and resultant superior OTFT characteristics were realized. We obtained a field-effect mobility of 1.6 cm²/Vs, a threshold voltage of −8.2 V, an on-off ratio of 10⁶, and a subthreshold swing of 55 mV/decade.     

Water-Surface-Mediated Precise Patterning of Organic Single-Crystalline Films via Double-Blade Coating for High-Performance Organic Transistors

Application-oriented growth of patterned organic semiconductor (OSC) thin films with a single domain is a nonnegotiable requirement for the manufacturing of high-performance organic electronic devices. However, the prevalent selective-wetting patterning method remains a challenge in controlling the density of nucleation events in microscale spaces, resulting in thin films with high grain boundary density and no preferential orientation spherulites. Herein, a simple double-blade-coating printing technique using a combination of wetting-patterned substrates to produce an array of highly crystalline OSC thin films is developed. Specifically, the approach confines the OSC crystallization on a molecular-flat water surface in specific areas, enabling a significant reduction in the number of nuclei. Consequently, patterned 2,7-dioctyl[1]benzothieno[3,2-b] benzothiophene (C₈-BTBT) thin films comprising single-crystal domains are achieved with an exceptionally high yield of 62.5%. The organic field-effect transistor array developed from such patterns of C₈-BTBT single-crystalline films exhibits an excellent average mobility of 11.5 cm² V⁻¹ s⁻¹ which is 12.5-fold higher compared to that of the reference sample fabricated via conventional single-blade coating. It is believed that this approach can be widely applied to other soluble organic materials, thereby opening up opportunities for fabricating multicomponent integrated electronics.     

退火温度对SnF2掺杂SnO2薄膜性能的影响

利用电子束蒸镀技术在石英玻璃上沉积SnF2掺杂SnO2(FTO)薄膜.研究了不同退火温度对FTO薄膜结构和光电性能的影响.研究结果表明:升高退火温度可促进FTO薄膜中晶粒逐渐变大,结晶度变好,同时薄膜在可见光范围内的透射率随着退火温度升高逐渐增加,吸收边发生蓝移,禁带宽度显著变宽,这是由于载流子浓度增加导致的Moss-Burstein效应.升高温度时,薄膜电学性能随着退火温度升高有了很大改善,700℃退火处理后得到电阻率低至2.74×101 Ω·cm、载流子浓度为2.09×1020 cm-3、迁移率为9.93 cm2·V 1·s 1的FTO薄膜.     

High-performance 2,9-DPh-DNTT organic thin-film transistor by weak epitaxy growth method

2,9-DPh-DNTT, an isomeric of diphenyl-dinaphtho[2,3-b:2′,3′-f]-thieno[3,2-b] thiophene (DPh-DNTTs), is an emerging candidate of high mobility organic semiconductor material. In this work, a high performance 2,9-DPh-DNTT organic thin-film transistor (OTFT) is fabricated by the method of weak epitaxy growth. The quality of 2,9-DPh-DNTT thin film was significantly improved when its epitaxial layer grows on an inducing layer of para-sexiphenyl (p-6P). Continuous large-area, highly ordered and terraced 2,9-DPh-DNTT polycrystalline thin films are obtained. The hole mobility of as-fabricated 2,9-DPh-DNTT thin-film transistor reaches up to 6.4 cm² V⁻¹s⁻¹. This simple process of preparing high mobility 2,9-DPh-DNTT thin-film transistor supplies a facile route of large-area OTFT fabrication.     

Morphology optimization for achieving air stable and high performance organic field effect transistors

To develop an all organic active matrix light emitting display required for large area thin display, electronic paper and electronic paints, Si-based thin film transistor has to be replaced with organic thin film transistor (OTFT). The most important issues in OTFT are the low charge carrier mobility and poor stability under ambient conditions, which critically depend on how organic thin films are grown on different substrates. Here we show that both these issues are correlated and can be overcome by certain surface morphology which can only be achieved through anisotropic growth. Careful control of different growth parameters can lead to unprecedented control on thin film morphology which has been shown to be engineered reversibly and reproducibly. High temperature and low evaporation rate increase the diffusive mobility of molecules, which are responsible for the stacking of molecules to higher length scales. By carefully choosing a temperature and evaporation rate, elongated rod-like grains were grown for achieving high performance and stable thin film transistors.     

Micro‐/Nanostructured Highly Crystalline Organic Semiconductor Films for Surface‐Enhanced Raman Spectroscopy Applications

The utilization of inorganic semiconductors for surface‐enhanced Raman spectroscopy (SERS) has attracted enormous interest. However, despite the technological relevance of organic semiconductors for enabling inexpensive, large‐area, and flexible devices via solution processing techniques, these π‐conjugated systems have never been investigated for SERS applications. Here for the first time, a simple and versatile approach is demonstrated for the fabrication of novel SERS platforms based on micro‐/nanostructured 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene (C8‐BTBT) thin films via an oblique‐angle vapor deposition. The morphology of C8‐BTBT thin films is manipulated by varying the deposition angle, thus achieving highly favorable 3D vertically aligned ribbon‐like micro‐/nanostructures for a 90° deposition angle. By combining C8‐BTBT semiconductor films with a nanoscopic thin Au layer, remarkable SERS responses are achieved in terms of enhancement (≈10⁸), stability (>90 d), and reproducibility (RSD < 0.14), indicating the great promise of Au/C8‐BTBT films as SERS platforms. Our results demonstrate the first example of an organic semiconductor‐based SERS platform with excellent detection characteristics, indicating that π‐conjugated organic semiconductors have a great potential for SERS applications.     

Growth of Large Crystalline Grains of Vanadyl‐Phthalocyanine without Epitaxy on Graphene

The performance of organic semiconductor thin films in electronic devices is related to their crystal structure and morphology, with charge transport mobility dependent on the degree of crystallinity and on the crystallographic orientation. Here organic molecular beam deposition of vanadyl phthalocyanine is studied on graphene and it is shown that crystalline grains up to several micrometers across can be formed at substrate temperatures of 155 °C, compared to room temperature grain sizes of ≈30 nm. Transmission electron microscopy confirms the presence of long range order at elevated substrate temperatures and reveals that the molecules are stacked in an edge‐on orientation, but are not epitaxially aligned to the graphene. The crystalline grain sizes are significantly larger on graphene than on disordered substrates such as graphene oxide and silicon oxide. The effect on charge transport is probed by conducting atomic force microscopy, with the high temperature films on graphene showing increased mobility and uniformity and decreased trap density. These results illustrate an important advantage for the integration of graphene electrodes with organic semiconductor devices: the homogeneous surface of graphene results in high diffusion and low nucleation rates for thin film growth, encouraging the formation of highly crystalline films even with nonepitaxial growth.     

并五苯有机薄膜晶体管电学性能研究

制作了以并五苯为半导体有源层材料的有机薄膜晶体管。用热氧化的方法制备了一层230nm的二氧化硅栅绝缘层并用原子力显微镜(AFM)分析了表面形貌。研究了器件的电学性能,得到的并五苯有机薄膜晶体管器件载流子迁移率为8.9×10-3cm2/V.s,器件的阈值电压和开关电流比分别为-8.2V和1.0×104。     

Mobility enhancement of DNTT and BTBT derivative organic thin-film transistors by triptycene molecule modification

Interface modification with a particular triptycene molecule that spontaneously forms a highly uniform molecule layer is a promising technique for realizing high-performance flexible organic thin-film transistors (OTFTs). Previous studies have shown that the triptycene-modified polymer surface enhances the crystallinity of the small-molecule organic semiconductor (OSC), DNTT (dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene), resulting in improved mobility. However, to date, the effectiveness of triptycene modification for the other OSCs has not been confirmed. Here, we report on the positive effect of triptycene layers on four different thienoacene-based OSCs (C₁₀-DNTT, DPh-DNTT, C₈-BTBT ([1]benzothieno[3,2-b][1]benzothiophene), and DPh-BTBT) in OTFTs. Regardless of the OSC type, triptycene-modified OTFTs are found to improve the field-effect mobility. A maximum effective mobility enhancement of 20-fold was obtained for C₁₀-DNTT OTFTs. Furthermore, detailed observations of the surface morphology of the OSCs via scanning electron microscopy revealed that the crystal grain size of the OSC thin films can be increased when triptycene modification is conducted.     

不同沟道宽长比有机薄膜晶体管性能的研究

以酞菁铜为有源层,二氧化硅为绝缘层,钛/金作为电极,制作了三种不同沟道宽长比的有机薄膜晶体管器件。通过对这三种器件的电学特性进行对比,分析了不同沟道宽长比对器件电学性能的影响。结果表明,沟道宽长比对器件的迁移率影响很小,阈值电压随着宽长比的增大而减小,漏电流随沟道宽长比的增大而增大;当源漏极间电压在一定范围内时,开态电流也随沟道宽长比的增大而增大。