BaTiO_3压电薄膜的制备及其性能研究

利用旋涂技术,在聚二甲基硅氧烷(PDMS)混合液中掺入不同质量分数(30%,50%,70%)的钛酸钡(BaTiO_3)纳米颗粒,并将混合物均匀涂在洁净的硅片表面进行旋涂处理;加热固化制得压电薄膜,并对压电薄膜进行极化处理,分别运用扫描电子显微镜(SEM),X线衍射(XRD)仪分析薄膜表面和BaTiO_3粉末。实验结果表明,薄膜内部BaTiO_3分布相对均匀,且其中BaTiO_3纳米颗粒为四方相。设计振动能量采集测试系统测试分析薄膜的输出开路电压和供电能力,分别用单悬臂梁振动和激振器敲击的形式对压电薄膜的输出特性进行研究。压电薄膜的输出电压峰-峰值与BaTiO_3的质量分数具有高度的一致性,在w(BaTiO_3)=70%时,输出电压最高,对应的峰-峰值为3.50V。     

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.     

Electric Field Tuning Molecular Packing and Electrical Properties of Solution‐Shearing Coated Organic Semiconducting Thin Films

Recent improvements in solution‐coated organic semiconductors (OSCs) evidence their high potential for cost‐efficient organic electronics and sensors. Molecular packing structure determines the charge transport property of molecular solids. However, it remains challenging to control the molecular packing structure for a given OSC. Here, the application of alternating electric fields is reported to fine‐tune the crystal packing of OSC solution‐shearing coated at ambient conditions. First, a theoretical model based on dielectrophoresis is developed to guide the selection of the optimal conditions (frequency and amplitude) of the electric field applied through the solution‐shearing blade during coating of OSC thin films. Next, electric field‐induced polymorphism is demonstrated for OSCs with both herringbone and 2D brick‐wall packing motifs in 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene and 6,13‐bis(triisopropylsilylethynyl) pentacene, respectively. Favorable molecular packing can be accessible in some cases, resulting in higher charge carrier mobilities. This work provides a new approach to tune the properties of solution‐coated OSCs in functional devices for high‐performance printed electronics.     

Measuring Domain Sizes and Compositional Heterogeneities in P3HT‐PCBM Bulk Heterojunction Thin Films with 1H Spin Diffusion NMR Spectroscopy

The application of ¹H spin diffusion nuclear magnetic resonance (NMR) is expanded to polymer‐fullerene blends for bulk heterojunction (BHJ) organic photovoltaics (OPV) by developing a new experimental methodology for measuring the thin films used in poly‐3‐hexylthiophene–phenyl C61‐butyric acid methyl ester (P3HT‐PCBM) OPV devices and by creating an analysis framework for estimating domain size distributions. It is shown that variations in common P3HT‐PCBM BHJ processing parameters such as spin‐coating speed and thermal annealing can significantly affect domain size distributions, which in turn affect power conversion efficiency. ¹H spin diffusion NMR analysis reveals that films spin‐cast at fast speeds in dichlorobenzene are primarily composed of small (<10 nm) domains of each component; these devices exhibit low power conversion efficiencies (η = 0.4%). Fast‐cast films improve substantially by thermal annealing, which causes nanometer‐scale coarsening leading to higher efficiency (η = 2.2%). Films spin‐cast at slow speeds and then slowly dried exhibit larger domains and even higher efficiencies (η = 2.6%), but do not benefit from thermal annealing. The ¹H spin diffusion NMR results show that a significant population of domains tens of nanometers in size is a common characteristic of samples with higher efficiencies.     

Organic Solid Solutions: Formation and Applications in Organic Light‐Emitting Diodes

To enhance the performance of organic devices, doping and graded mixed‐layer structures, formed by co‐evaporation methods, have been extensively adopted in the formation of organic thin films. Among the criteria for selecting materials systems, much attention has been paid to the materials' energy‐band structure and carrier‐transport behavior. As a result, some other important characteristics may have been overlooked, such as material compatibility or solubility. In this paper, we propose a new doping method utilizing fused organic solid solutions (FOSSs) which are prepared via high‐pressure and high‐temperature processing. By preparing fused solid solutions of organic compounds, the stable materials systems can be selected for device fabrication. Furthermore, by using these FOSSs, doping concentration and uniformity can be precisely controlled using only one thermal source. As an example of application in organic thin films, high‐performance organic light‐emitting diodes with both single‐color and white‐light emission have been prepared using this new method. Compared to the traditional co‐evaporation method, a FOSS provides us with a more convenient way to optimize the doping system and fabricate relatively complicated organic devices.     

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.     

Spray‐Coated Silver Nanowires as Top Electrode Layer in Semitransparent P3HT:PCBM‐Based Organic Solar Cell Devices

Silver nanowire (Ag NW) thin films are investigated as top electrodes in semitransparent inverted organic solar cells. The performance of semitransparent poly(3‐hexylthiophene‐2,5‐diyl):[6,6]‐phenyl‐C61‐butyric acid methyl ester (P3HT:PCBM) organic solar cells with Ag NW top electrode layers is found to match very closely the performance of reference devices based on thermally evaporated, highly reflective metal silver top electrodes. The optical losses of the semitransparent electrodes are investigated in detail and analyzed in terms of transmission, scattering, and reflection losses. The impact on an external back reflector is shown to increase the light harvesting efficiency of optically thin devices. Further analysis of transparent devices under illumination from the indium tin oxide (ITO) backside and through the Ag NW front electrode open the possibility to gain deep insight into the vertical microstructure related devices performance. Overall, Ag NW top electrodes are established as a serious alternative to TCO based electrodes. Semitransparent devices with efficiencies of over η = 2.0% are realized.     

Spatial Mapping of Morphology and Electronic Properties of Air‐Printed Pentacene Thin Films

To accelerate the pace of materials discovery and application, comprehensive links need to be established between a material's structure, properties, and process conditions used to obtain the material and/or final application format. This work examines the dry printing of pentacene thin film transistor (TFT) channels by guard flow‐enhanced organic vapor jet printing (GF‐OVJP), a technique that enables direct, solvent‐free, additive patterning of device‐quality molecular semiconductors in air. Deposition in air entails non‐trivial effects at the boundary between ambient surroundings and the gas jet carrying the semiconductor vapor that influence the morphology and properties of the resulting electronic devices. Synchrotron X‐ray diffraction is employed, complemented by measurement of electronic properties of GF‐OVJP deposited films in a TFT to reveal how the morphology and electronic properties of the films depend on thickness, location within the printed pattern, nozzle translation velocity, and other process parameters. The hole field‐effect mobility of the printed pentacene film is linked quantitatively with its crystallinity, as well as with extent of exposure to ambient air during deposition. The analysis can be extended to accurately predict the performance of devices deposited in air by GF‐OVJP, which are demonstrated here for a planar, large area deposit.     

Lateral Phase Separation Gradients in Spin‐Coated Thin Films of High‐Performance Polymer:Fullerene Photovoltaic Blends

In this study, it is demonstrated that a finer nanostructure produced under a rapid rate of solvent removal significantly improves charge separation in a high‐performance polymer:fullerene bulk‐heterojunction blend. During spin‐coating, variations in solvent evaporation rate give rise to lateral phase separation gradients with the degree of coarseness decreasing away from the center of rotation. As a result, across spin‐coated thin films the photocurrent at the first interference maximum varies as much as 25%, which is much larger than any optical effect. This is investigated by combining information on the surface morphology of the active layer imaged by atomic force microscopy, the 3D nanostructure imaged by electron tomography, film formation during the spin coating process imaged by optical interference and photocurrent generation distribution in devices imaged by a scanning light pulse technique. The observation that the nanostructure of organic photovoltaic blends can strongly vary across spin‐coated thin films will aid the design of solvent mixtures suitable for high molecular‐weight polymers and of coating techniques amenable to large area processing.     

Supramolecular Order of Solution‐Processed Perylenediimide Thin Films: High‐Performance Small‐Channel n‐Type Organic Transistors

N,N′‐1H,1H‐perfluorobutyl dicyanoperylenecarboxydiimide (PDIF‐CN₂), a soluble and air stable n‐type molecule, undergoes significant reorganization upon thermal annealing after solution deposition on several substrates with different surface energies. Interestingly, this system exhibits an exceptional edge‐on orientation regardless of the substrate chemistry. This preferential orientation is rationalized in terms of strong intermolecular interactions between the PDIF‐CN₂ molecules. The presence of a pronounced π–π stacking is confirmed by combining near‐edge X‐ray absorption fine structure spectroscopy (NEXAFS), dynamic scanning force microscopy (SFM) and surface energy measurements. The remarkable charge carrier mobility measured in field‐effect transistors, using both bottom‐ and top‐contact (bottom‐gate) configurations, underlines the importance of strong intermolecular interactions for the realization of high performing devices.     

Critical Role of Triplet Exciton Interface Trap States in Bilayer Films of NPB and Ir(piq)3

Investigations are carried out into triplet transfer in bilayer films of NPB (N,N´‐diphenyl‐N,N´‐bis(1‐naphthyl)‐1,1´‐biphenyl‐4,4?‐diamine) and Ir(piq)₃ (Iridium (III) Tris(1‐phenylisoquinoline) using laser light pulses to excite the upper surface of the NPB, and thereafter observing the decay dynamics in the Ir(piq)₃ layer situated beneath the NPB. The NPB layer thickness is varied from 13 nm to 80 nm. The results show that up to 200 ns after excitation, the multiexponential decay of directly excited Ir(piq)₃ is observed, thereafter the decay is monoexponential. It is concluded that this monoexponential decay after 200 ns is due to triplets that are transferred to the Ir(piq)₃ via migration from the NPB. The thicker the NPB layer the longer it takes for the reservoir of NPB triplets to deplete via the Ir(piq)₃, with the result that the apparent monoexponential lifetime of the Ir(piq)₃ increases as the thickness of the NPB films increases. Based on time resolved spectra and decays, it is concluded that triplets arriving from NPB are trapped at interface sites of Ir(piq)₃ and do not migrate directly to the bulk states of Ir(piq)₃. A model based on exciton diffusion kinetics, including the presence of interface trap sites, is described, which accurately predicts this behavior.     

Successive Spray Deposition of P3HT/PCBM Organic Photoactive Layers: Material Composition and Device Characteristics

Controlling the active layer composition in organic electronic devices represents one of the major challenges in their fabrication. In particular, the composition of mixed donor/acceptor active layers for photosensitive device applications is known to strongly influence device performance. Here, an alternative approach for the preparation of organic heterojunction photoactive layers by successive spray deposition of the donor material, poly(3‐hexylthiophene) (P3HT), and acceptor material, [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM), is reported. Optical absorption spectra, X‐ray reflectivity, and cross‐sectional transmission electron microscopy investigations are used to indicate the penetration of PCBM into a previously deposited P3HT layer and the spontaneous formation of a bulk heterojunction (BHJ) within the active layer, which provides the large interfacial area needed for efficient exciton dissociation. It is shown that organic photodiodes composed of photoactive layers prepared using this fabrication method exhibit a performance comparable to conventional BHJ devices in which the active layer is rigorously blended in advance. Moreover, separate handling of the individual materials and their deposition from distinct solutions enables an enhanced control of the active layer composition and hence increases the ability of tuning device characteristics.     

Independent Tuning of Optical Transparency Window and Electrical Properties of Epitaxial SrVO3 Thin Films by Substrate Mismatch

Transparent metallic oxides are pivotal materials in information technology, photovoltaics, or even in architecture. They display the rare combination of metallicity and transparency in the visible range because of weak interband photon absorption and weak screening of free carriers to impinging light. However, the workhorse of current technology, indium tin oxide (ITO), is facing severe limitations and alternative approaches are needed. AMO₃ perovskites, M being a nd¹ transition metal, and A an alkaline earth, have a genuine metallic character and, in contrast to conventional metals, the electron–electron correlations within the nd¹ band enhance the carriers effective mass (m*) and bring the transparency window limit (marked by the plasma frequency, ω_p*) down to the infrared. Here, it is shown that epitaxial strain and carrier concentration allow fine tuning of optical properties (ω_p*) of SrVO₃ films by modulating m* due to strain‐induced selective symmetry breaking of 3d‐t_2g(xy, yz, xz) orbitals. Interestingly, the DC electrical properties can be varied by a large extent depending on growth conditions whereas the optical transparency window in the visible is basically preserved. These observations suggest that the harsh conditions required to grow optimal SrVO₃ films may not be a bottleneck for their future application.     

Nanoporous Silver Thin Films: Multifunctional Platforms for Influencing Chain Morphology and Optical Properties of Conjugated Polymers

Disordered nanoporous silver (NPAg) thin films fabricated by a thermally assisted dewetting method are employed as a platform to influence chain alignment, morphology, and optical properties of three well‐known conjugated polymers. Grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) measurements show that the porous structure of the metal induces close π–π stacking of poly(3‐hexylthiophene) (P3HT) chains and extended, planar chain conformations of poly(9,9‐di‐n‐octylfluorenyl‐2,7‐diyl) (PFO) and poly[(9,9‐di‐n‐octylfluorenyl‐2,7‐diyl)‐alt‐(benzo[2,1,3]thiadiazol‐4,8‐diyl)] (F8BT). A greater degree of vertically‐oriented P3HT chains are found on NPAg compared with planar Ag. However, PFO and F8BT chain alignment is only affected when pore size is large. The optical properties of NPAg films are investigated by transmission and back‐scattering spectroscopies. Strong back‐scattering is observed for all NPAg morphologies, especially for NPAg with small pore sizes. Photoluminescence spectroscopy of conjugated polymer layers on NPAg showed pronounced emission enhancements (up to factors of 26) relative to layers on glass. The enhancements are attributed primarily to: 1) redistribution of conjugated polymer emission by Ag; 2) redirection of emission by polymer‐filled nanopores; and 3) local electromagnetic field effects. This work demonstrates the potential of NPAg‐thin films to influence molecular chain morphology and to improve light‐extraction in organic optoelectronic devices.     

Solution‐Processed Nanoporous Organic Semiconductor Thin Films: Toward Health and Environmental Monitoring of Volatile Markers

Porous materials are ubiquitous in nature and have found a wide range of applications because of their unique absorption, optical, mechanical, and catalytic properties. Large surface‐area‐to‐volume ratio is deemed a key factor contributing to their catalytic properties. Here, it is shown that introducing tunable nanopores (50–700 nm) to organic semiconductor thin films enhances their reactivity with volatile organic compounds by up to an order of magnitude, while the surface‐area‐to‐volume ratio is almost unchanged. Mechanistic investigations show that nanopores grant direct access to the highly reactive sites otherwise buried in the conductive channel of the transistor. The high reactivity of nanoporous organic field‐effect transistors leads to unprecedented ultrasensitive, ultrafast, selective chemical sensing below the 1 ppb level on a hundred millisecond time scale, enabling a wide range of health and environmental applications. Flexible sensor chip for monitoring breath ammonia is further demonstrated; this is a potential biomarker for chronic kidney disease.