Polaron and ion diffusion in a poly(3-hexylthiophene) thin-film transistor gated with polymer electrolyte dielectric

Electrolytes are finding applications as dielectric materials in low-voltage organic thin-film transistors (OTFT). The presence of mobile ions in these materials (polymer electrolytes or ion gels) gives rise to very high capacitance (>10 μF/cm²) and thus low transistor turn-on voltage. In order to establish fundamental limits in switching speeds of electrolyte gated OFETs, we carry out in situ optical spectroscopy measurement of a poly(3-hexylthiophene) (P3HT) OTFT gated with a LiClO₄:poly(ethyleneoxide) (PEO) dielectric. Based on spectroscopic signatures of molecular vibrations and polaron transitions, we quantitatively determine charge carrier concentration and diffusion constants. We find two distinctively different regions: at V _G≥−1.5 V, drift-diffusion (parallel to the semiconductor/dielectric interface) of hole-polarons in P3HT controls charging of the device; at V _G<−1.5 V, electrochemical doping of the entire P3HT film occurs and charging is controlled by drift/diffusion (perpendicular to the interface) of ClO₄ ⁻ counter ions into the polymer semiconductor.     

Electrochemical formation and properties of thin polyaniline films on Au(111) and p-Si(111)

The specific aspects of phase formation phenomena involved in electrodeposition of conducting polymer layers are critically discussed. The mechanism of formation and the properties of electrodeposited thin polyaniline (PANI) films on Au(111) and p-Si(111) are investigated by means of transient measurements, cyclic voltammetry, electrochemical impedance spectroscopy and atomic force microscopy (AFM). Experimental results show that the initial stages of PANI electrodeposition on Au(111) can be described by a model including progressive appearance and preferential 2D growth of polymer islands. The electropolymerization process on p-Si(111) substrates is preceded by anodic formation of an inhomogeneous thin SiO₂ layer giving rise to a progressive appearance and growth of 3D PANI islands. The electrochemical redox properties of electrodeposited PANI films on p-Si(111) are influenced strongly by the electronic band structure of silicon. PACS 81.10.Aj; 82.45.Wx; 82.45.Vp     

Mechanism of the redox process of conducting polymers

The reversible redox process of electrochemically formed conducting polymers (poly-aniline, poly-3-methylthiophene, poly-carbazole, and poly-bithiophene) was investigated by current transients of potentiostatic steps, impedance spectroscopy, and by mass transients from the electrochemical quartz micro balance. The polymer film thickness (18 nm ≤ d ≤ 6700 nm) and the electrolyte (aqueous H₂SO₄, HClO₄, trichloroacetic acid, and p-toluenesulphonic acid, or non-aqueous acetonitrile/Et₄N ClO₄) was varied. The redox process is a complex sequence of steps. The oxidation starts with a field supported, non-homogeneous formation of conducting pathes. 5 to 10% of the total charge are sufficient to convert the polymer to the conducting state. Up to 50% of the total charge are consumed by a mechanism which involves proton transport. The further redox process requires a transport of anions from the electrolyte. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995     

非晶/结晶共混对聚合物光伏电池性能的影响

以局域规整聚（3-己基噻吩） （P3HT）制备了TiO₂/聚合物型双层结构光伏电池.利用稳态电流-电压测试和动态强度调制光电压谱,结合差热分析、吸收光谱和荧光光谱, 研究了非晶支化聚亚乙基亚胺（BPEI）作为P3HT膜层的添加成分对TiO₂/P3HT双层电池性能的影响.由于P3HT链的高结晶性,使得TiO₂/P3HT界面接触不好,导致电池性能差.当在P3HT中共混重量比W_BPEI/P3HT=1％—5％的BPEI时,电池性能得到显著改善;尤其是当W_BPEI/P3HT= 1％时,电池表现出近0.8V的开路电压和20μA/cm²的短路电流.结果表明BPEI对电池性能的影响不是源于P3HT-BPEI共混体系光学性能的变化,而主要是由于其改变了TiO₂/P3HT界面接触性能.BPEI对TiO₂/P3HT界面接触有两个相互竞争的影响,这取决于P3HT-BPEI共混体系的组成.一方面,通过降低P3HT的结晶度和增强与TiO₂表面的相互作用,改善P3HT链在TiO₂ 表面的附着;另一方面,当BPEI含量过高时,BPEI在TiO₂表面的附着量将增加,反而会阻碍P3HT与TiO₂表面的接触.良好的TiO₂/P3HT界面接触有利于提高激子的界面分离效率、光生电子的寿命和电池效率.本文结果有望为聚合物光伏电池性能的改善提供新的认识和方法. 关键词： 聚（3-己基噻吩） 二氧化钛 共轭聚合物 光伏电池     

Investigation of polymer/inorganic hybrid photovoltaic device using quantum dots as the interface modifier

CdS quantum dots (QDs) were introduced as an interface modifier in the poly(3-hexylthiophene) (P3HT)/TiO₂ nanorod arrays hybrid photovoltaic device. The presence of CdS QDs interlayer was found to provide enhanced light absorption, increased interfacial recombination resistance at the P3HT/TiO₂ interfaces, thus leading to a lower recombination rate of the electrons due to the stepwise structure of band edge in P3HT/CdS/TiO₂, which accounts for the observed enhanced photocurrent and photovoltage of the hybrid solar cells. The optimized performance was achieved in P3HT/CdS/TiO₂ hybrid solar cells after deposition of CdS QDs for 10 cycles, with a power conversion efficiency of 0.57 %, which is nearly ten times higher than that of P3HT/TiO₂. The findings indicate that inorganic semiconductor quantum dots provide effective means to improve the performance of polymer/TiO₂ hybrid solar cells.     

Performance and stability studies of inverted polymer solar cells with TiO2 film as a buffer layer

TiO₂ based inverted polymer solar cells (PSCs) with a structure of fluorine-doped tin oxide (FTO)/TiO₂/P3HT:PCBM/PEDOT:PSS/Ag presented excellent air stabilities,; the power conversion efficiency (PCE) of devices exhibited only 15 % decay as compared to the highest value while being exposed in air-condition for more than 20 days. Interestingly, an overall enhancement of PCE from 3.5 % to 3.9 % was observed while the PSCs were exposed in air-condition up to 3 days; the improvement of performance was attributed to the TiO₂ films’ oxygen and water protection effect and the oxidation of Ag, which will benefit to form an effective work function match with the HOMO of P3HT leading to improved ohmic contact. However, the performance slowly decreased when the exposure time remains longer due to the physical adsorbed oxygen. UV–ozone treatment on the TiO₂ films’ leads to the formation of a metal-deficient oxide that results in a decreased PCE for the devices. Finally, X-ray photo-emission spectroscopy (XPS) was used to analyze the compositional changes of the TiO₂ films while they were exposed in air-condition or treated by UV–ozone.     

Surface redox induced bipolar switching of transition metal oxide films examined by scanning probe microscopy

The bipolar resistive switching mechanisms of a p-type NiO film and n-type TiO₂ film were examined using local probe-based measurements. Scanning probe-based current–voltage (I–V) sweeps and surface potential/current maps obtained after the application of dc bias suggested that resistive switching is caused mainly by the surface redox reactions involving oxygen ions at the tip/oxide interface. This explanation can be applied generally to both p-type and n-type conducting resistive switching films. The contribution of oxygen migration to resistive switching was also observed indirectly, but only in the cases where the tip was in (quasi-) Ohmic contact with the oxide.     

Direct imprinting of ordered and dense TiO2 nanopore arrays by using a soft template for photovoltaic applications

Highly ordered and dense TiO₂ nanopore arrays are directly nanoimprinted on a transparent conductive glass substrate by using a polymethylmethacrylate/polydimethylsiloxane (PMMA/PDMS) composite soft template, which is replicated from an anodic aluminum oxide (AAO) replica mold. Results indicate that heat infiltration under vacuum conditions can ensure complete filling of PMMA into the AAO pores, and that free-standing PMMA nanorods with an aspect ratio more than 5 can be obtained by adjusting the AAO pore depth based on a freeze-drying technique. TiO₂ nanopore arrays with different diameters from 30 to 300 nm and inter-pore distances between 70 and 450 nm can be easily fabricated by using the corresponding templates with different sizes. Preliminary solar cells are also assembled with a heterojunction of conjugated polymer/TiO₂ nanopore arrays. Results indicate that the construction of poly-(3-hexylthiophene) (P3HT)/TiO₂ nanopore arrays can be more helpful in quenching the PL emission of P3HT than that of P3HT/flat TiO₂ film, and a maximum efficiency of about 0.32% can be obtained for a photovoltaic device with a TiO₂/[6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM)/P3HT structure.     

The inverted solar cells with the polymer:fullerene blend film possessing a stratified composition profile

The inverted polymer:fullerene solar cells with structure of ITO/TiO₂/P3HT:PCBM/MoO₃/Al have been fabricated, where P3HT and PCBM stand for poly (3-hexylthiophene) and [6,6]-phenyl C₆₁-butyric acid methyl ester, respectively. It is discovered that the P3HT:PCBM blend film manipulated into the improved stratification structure, characterized as P3HT crystallite-rich zone close to the top surface and PCBM constituent-rich zone adjacent to the bottom surface, can offer nearly the same power conversion efficiency of solar cell, compared to the one grown into the bulk heterojunction structure, characterized as the bicontinuous interpenetrating network of P3HT and PCBM. We provide an alternative insight to the morphology control of inverted polymer:fullerene solar cells.     

Ionic conduction behavior in PVC–PEG blend polymer electrolytes upon the addition of TiO2

The blend-based polymer electrolyte consisting of poly (vinyl chloride) (PVC) and poly (ethylene glycol) (PEG) as host polymers and lithium perchlorate (LiClO₄) as the complexing salt was studied. An attempt was made to investigate the effect of TiO₂ concentration in the unplasticized PVC–PEG polymer electrolyte system. The XRD and FTIR studies confirm the formation of a polymer–salt complex. The conductivity results indicate that the incorporation of ceramic filler up to a certain concentration (15 wt.%) increases the ionic conductivity and upon further addition the conductivity decreases. The maximum ionic conductivity 0.012 × 10⁻⁴ S cm⁻¹ is obtained for PVC–PEG–LiClO₄–TiO₂ (75–25–5–15) system. Thermal stability of the polymer electrolyte is ascertained from TG/DTA studies.     

Novel properties of nanoscale organic–inorganic systems and photonic crystals — conducting polymers in nanoscale periodic structures,microcavities and photonic crystals

Conducting polymer/C₆₀and C₆₀doped conducting polymer/C₆₀heterojunctions have been fabricated and found to exhibit remarkably enhanced photoresponse due to the highly effective photoinduced charge transfer at the interface. In conducting polymer/C₆₀alkali metal nanoscale composite systems, multiphase superconductivity has been clarified and explained by taking the coupling of nanoscale grains by Josephson junctions into consideration. As examples of intramolecular organic-inorganic combined systems, unique electrical and optical characteristics have been revealed in oligosilanylene oligophenylene polymers. Electroluminescence has been demonstrated in organic-inorganic junction devices such as conducting polymer/porous Si and conducting polymer/diamond junctions. Conducting, polymer-based nanoscale multilayer systems have been studied utilizing molecular self-assembly method and novel photosensitive characteristics have been revealed. \indent Novel optical and electrical properties of conducting polymers infiltrated in a photonic crystal, synthetic opal made of SiO₂spheres of several hundred nm in diameter, and also a conducting polymer replica have been revealed. A clear diffraction pattern was observed in a photonic crystal infiltrated with conducting polymers, and transmission spectra are dependent on various ambient conditions. Their photoluminescence (PL) spectra, spectral narrowing of PL and lasing characteristics at relatively low optical excitation have also been clarified. Novel conducting characteristics of conducting polymers in a photonic crystal that was prepared by pyrolysis of a polymer replica of opal have also been observed.     

Interface morphologies and magnetization characteristics of Co70Fe30 thin films deposited on conjugated polymer thin films

The surface and interface morphology and magnetization characteristics of Co₇₀Fe₃₀ thin films deposited on bare glass and p-Si/SiO₂ substrates and on conjugated polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) thin films on such substrates have been studied by atomic force microscopy and magneto-optic Kerr effect. It was found that the average absolute magnitude of the coercive field of Co₇₀Fe₃₀ correlates with the roughness of the underlayer prior to Co₇₀Fe₃₀ deposition. P3HT deposited on p-Si/SiO₂ substrates possesses an increased surface roughness as compared to the p-Si/SiO₂ surface, but displays a decreased surface roughness as compared to the one of a bare glass substrate.     

Effects of the compliance current on the resistive switching behavior of TiO2 thin films

Nanocrystalline TiO₂ thin films were fabricated on Pt(111)/Ti/SiO₂/Si substrates by the thermal oxidation of evaporated Ti films. Effects of the compliance current on the resistive switching behavior of the Pt/TiO₂/Pt sandwich structures were studied in detail. The reset current increased when the compliance current increased from 10 mA to 20 mA. When the compliance current exceeded 20 mA, the switching behavior disappeared, which could be attributed to the change of the conducting behavior in the low-resistance state. A resistance change ratio of as high as 10² was obtained between the high-resistance state and the low-resistance state. The study of the effect of compliance current contributes to obtaining stable and reliable resistive switching behavior for nonvolatile memory applications.     

Polarons in linear chains of fullerenes

Polaron states in linear chains of fullerenes are studied with the use of the generalized model of Su-Shrieffer-Heeger (SSH) for the intermolecular and intramolecular degrees of freedom. Electron charge distributions over the molecular surface and Jahn-Teller distortions of carbon atoms in C₆₀ are calculated self-consistently for linear C₆₀ polymer and C ₆₀ ⁻ polyanion chains. A polaron band narrowing is examined. It is shown that the polymerization of C₆₀ molecules in phase transitions may be caused by the cooperative Jahn-Teller effect. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 8, 521–525 (25 October 1996) Published in English in the original Russian Journal. Edited by Steve Torstveit.     

共轭聚合物中链内无序效应对极化子输运的影响

基于扩展的Su-Schrieffer-Heeger紧束缚模型, 利用非绝热动力学方法研究了链内无序效应对共轭聚合物中极化子输运机制的影响. 研究发现, 极化子的输运由外加电场和链内无序效应共同作用的结果所决定. 在一般情况下, 链内无序效应不利于极化子的输运, 但随着电场强度的增大, 无序对极化子输运的影响减小. 关键词： 共轭聚合物 极化子输运 链内无序     

Microfabrication of gold dots in SiO2/TiO2 glass films by two-photon absorption

Photogeneration of Au nanoparticles in SiO₂/TiO₂ glass films was carried out by two-photon absorption with a femtosecond pulse laser. Exquisite microdot-arrays of Au with micrometer spatial resolution were achieved by scanning of the focused laser beam. These structures were constructed in SiO₂/TiO₂ glass films by a sol–gel method. The sol–gel method demonstrated that Au dots microarray are fabricated at any position by two-photon absorption in the glass. The results show the utility of a two-photon absorption technique in the fabrication of complicated patterns with metal particles.     

Deposition and characterization of binary Al2O3/SiO2 coating layers on the surfaces of rutile TiO2 and the pigmentary properties

Binary Al₂O₃/SiO₂-coated rutile TiO₂ composites were prepared by a liquid-phase deposition method starting from Na₂SiO₃·9H₂O and NaAlO₂. The chemical structure and morphology of binary Al₂O₃/SiO₂ coating layers were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, TG-DSC, Zeta potential, powder X-ray diffraction, and transmission electron microscopy techniques. Binary Al₂O₃/SiO₂ coating layers both in amorphous phase were formed at TiO₂ surfaces. The silica coating layers were anchored at TiO₂ surfaces via Si-O-Ti bonds and the alumina coating layers were probably anchored at the SiO₂-coated TiO₂ surfaces via Al-O-Si bonds. The formation of continuous and dense binary Al₂O₃/SiO₂ coating layers depended on the pH value of reaction solution and the alumina loading. The binary Al₂O₃/SiO₂-coated TiO₂ composites had a high dispersibility in water. The whiteness and brightness of the binary Al₂O₃/SiO₂-coated TiO₂ composites were higher than those of the naked rutile TiO₂ and the SiO₂-coated TiO₂ samples. The relative light scattering index was found to depend on the composition of coating layers.     

亚纳米厚的氧化铝包裹层可以显著提高负载型金纳米颗粒催化剂的热稳定性

负载型金纳米颗粒催化剂在许多催化反应中展现出非常好的催化活性,但是金纳米颗粒在高温等反应条件下容易烧结团聚,极大地限制了金催化剂的应用。利用原子层沉积技术在Au/TiO₂催化剂表面分别精确沉积了一层超薄的二氧化钛和氧化铝包裹层,并对比研究了包裹层对金纳米颗粒的热稳定性影响。原位红外漫反射CO吸附和x-射线光电子能谱数据证实了氧化物包裹层的存在。发现亚纳米厚的氧化铝包裹层能够在600 C完全避免金纳米颗粒的团聚;相反,二氧化钛包裹层对金纳米颗粒稳定性的提高没有明显效果。通过CO氧化探针反应的活性测试,发现随着煅烧温度的升高氧化铝包裹的Au/TiO₂ 催化剂的活性逐渐提高,表明高温处理可以促进被包裹金原子的暴露并表现出催化活性。提供了提高金纳米颗粒稳定性的有效方法,为拓展金催化剂在条件苛刻的反应中的应用奠定了技术基础.     

Synchrotron-Radiation Photoemission Study of Growth and Stability of Au Clusters on Rutile TiO2(110)-1×1

利用同步辐射高分辨光电子能谱研究了金团簇在部分还原TiO₂-(1×1)表面的生长和稳定性．价带谱实验结果观察到非常少量金团簇的沉积导致了Ti3+的3d峰完全消失,表明金团簇成核在TiO₂-(1×1)表面的氧缺陷位．Au4f芯电子光电子能谱实验结果证明了TiO₂-(1×1)表面氧缺陷位向金团簇转移电荷．还对比研究了化学剂量比和部分还原的TiO₂-(1×1)表面上金团簇的热稳定性．当金团簇尺寸相近时部分还原的TiO₂-(1×1)表面上金团簇要比化学剂量比的TiO₂-(1×1)面上金团簇稳定;在相同的表面上尺寸大的金团簇要比尺寸小的金团簇稳定．     

Synthesis and application of the solar cell of poly(3-hexylthiophene)/Fe N/titanium dioxide nanocomposite material

A series of nanocomposites of poly(3-hexylthiophene) with Fe N-doped TiO₂ (P3HT/Fe N/TiO₂) were synthesized by the chemical method in situ. The structure of the prepared composites was characterized using X-ray diffraction patterns (XRD), infrared spectroscopy (IR), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Optical and electrochemical properties were determined using UV-vis spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. These tests indicated that P3HT/Fe N/TiO₂ is a new p-n semiconductor. Two solar cells based on P3HT/Fe N/TiO₂ were manufactured and studied.