Yu-Chieh Tu

Correlating interface heterostructure, charge recombination, and device efficiency of poly(3-hexyl thiophene)/TiO2 nanorod solar cell.

The charge recombination rate in poly(3-hexyl thiophene)/TiO(2) nanorod solar cells is demonstrated to correlate to the morphology of the bulk heterojunction (BHJ) and the interfacial properties between poly(3-hexyl thiophene) (P3HT) and TiO(2). The recombination resistance is obtained in P3HT/TiO(2) nanorod devices by impedance spectroscopy. Surface morphology and phase separation of the bulk heterojunction are characterized by atomic force microscopy (AFM). The surface charge of bulk heterojunction is investigated by Kelvin probe force microscopy (KPFM). Lower charge recombination rate and lifetime have been observed for the charge carriers in appropriate heterostructures of hybrid P3HT/TiO(2) nanorod processed via high boiling point solvent and made of high molecular weight P3HT. Additionally, through surface modification on TiO(2) nan,orod, decreased recombination rate and longer charge carrier lifetime are obtained owing to creation of a barrier between the donor phases (P3HT) and the acceptor phases (TiO(2)). The effect of the film morphology of hybrid and interfacial properties on charge carrier recombination finally leads to different outcome of photovoltaic I-V characteristics. The BHJ fabricated from dye-modified TiO(2) blended with P3HT exhibits 2.6 times increase in power conversion efficiency due to the decrease of recombination rate by almost 2 orders of magnitude as compared with the BHJ made with unmodified TiO(2). In addition, the interface heterostructure, charge lifetime, and device efficiency of P3HT/TiO(2) nanorod solar cells are correlated.

Omniphobic Low Moisture Permeation Transparent Polyacrylate/Silica Nanocomposite

We report the development of low moisture permeation and transparent dense polyacrylate/silica nanocomposite material that can exhibit both superhydrophobic and oleophobic (omniphobic) properties. The material was prepared by a three-step process. The first step involved the preparation of UV polymerizable solventless hybrid resin and the fabrication of nanocomposite. The hybrid resin consisted of a mixture of acrylate monomer, initiator, and acrylate-modified different size silica nanoparticles. The second step was to roughen the surface of the nanocomposite with unique nanotexture by oxygen plasma. In the third step, we applied a low surface tension fluoro monolayer on the treated surface. The nanocomposite exhibits desired superhydrophobicity and oleophobicity with a water contact angle of 158.2° and n-1-octadecene contact angle of 128.5°, respectively; low moisture permeation of 1.44 g·mm/m(2)·day; and good transparency (greater than 82% at 450-800 nm for ~60 μm film). The material has potential applications in optoelectronic encapsulation, self-cleaning coating, etc.

Improving the electron mobility of TiO2 nanorods for enhanced efficiency of a polymer–nanoparticle solar cell

The poly(3-hexyl thiophene):TiO2 nanorod (P3HT:TiO2) solar cell has a better thermal stability than the P3HT:PCBM solar cell; however, the former has a lower power conversion efficiency (PCE) than the latter. We would like to enhance the PCE of P3HT:TiO2 solar cell by improving the electron mobility of anatase TiO2 nanorods. Two novel approaches: (1) ripening and (2) boron doping for TiO2 nanorods were explored. TiO2 nanorods were synthesized first by sol–gel process in the presence of an oleic acid surfactant at 98 °C for 10 h. The size of the TiO2 nanocrystal is about 35 nm in length and 5 nm in diameter. The insulating oleic acid on the TiO2 nanorods was replaced by pyridine (as-synthesized TiO2) for good compatibility and charge transport between P3HT and TiO2 in the application of hybrid P3HT:TiO2 nanorod solar cells. The crystallinity of the as-synthesized TiO2 nanorods was increased through ripening (120 °C, 24 h) by using an autoclave reactor while the size of the nanocrystals was not significantly changed. Boron doped TiO2 nanorods (B-doped TiO2) were synthesized using the same sol–gel process of as-synthesized TiO2 nanorods but by replacing 0.7 at.% Ti with B using boron n-butoxide instead of titanium tetraisopropoxide. The UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses indicate the B is present in TiO2 nanorods as substitutional defects which can be either Ti–O–B or O–Ti–B bonding, with a B 1 s binding energy of 192.1 eV. The ripening process is more effective at increasing the crystallinity of TiO2 nanorods than boron doping, as shown by XRD and Raman spectroscopy. The electron mobility of the TiO2 nanorods is improved from 6.21×10−5 to 2.33×10−4 (cm2 V−1 s) and 5.27×10−4 (cm2 V−1 s) for ripened TiO2 and B-doped TiO2, respectively, as compared with as-synthesized TiO2. The PCE of P3HT:TiO2 solar cells was increased by 1.31 times and 1.79 times under A. M. 1.5 illumination for ripened and B-doped TiO2, respectively, as compared with as-synthesized TiO2. The B-doped TiO2 has the highest mobility and PCE, mainly due to the presence of partially reduced Ti4+ by boron atom with delocalized electrons.

Hybrid poly(3-hexyl thiophene)–TiO2 nanorod oxygen sensor

Conjugated polymers are promising materials for oxygen sensing owing to their specific interaction with oxygen molecules and also advantages of low cost, easy processing and room temperature operation. The present work for the first time demonstrates an oxygen sensing material of poly(3-hexylethiophene) (P3HT)–TiO2 nanorod hybrid thin film which reveals considerable improvement of sensing response as compared to the pristine P3HT film. The effects of hybrid composition and film thickness on sensing performance were systematically investigated. Kelvin probe force microscopy (KPFM) was employed to understand the mechanism of oxygen sensing including the control of surface morphologies and electronic properties by TiO2 incorporation. The hybrid material developed in this study is helpful in the advancement of room temperature oxygen sensing technology.

High refractive index transparent nanocomposites prepared by in situ polymerization

High refractive index transparent nanocomposites have been developed by in situ polymerization of a precursor that contains functional monomers and surface modified anatase TiO2 nanoparticles for optoelectronic applications. The monomers are in the liquid form, so environmentally friendly solventless precursors can be prepared. The precursor can be processed into various shapes or thick films (>50 microns) of the nanocomposite. The relationships of the chemical structure of the organic matrix, nanoparticle content and dispersity with the refractive index, transparency, mechanical and thermal properties are systematically investigated. The refractive index, and mechanical and thermal properties of the nanocomposite are increased with increasing TiO2 content and aromatic structure in the organic matrix due to their rigid characteristics. The transparency of the nanocomposite is increased with increasing TiO2 content and dispersity. At the same loading of nanoparticles, the higher dispersity and the better transparency are due to the less extent of Rayleigh scattering. At 18 vol% (60 wt%) of TiO2, the acetic acid modified TiO2/poly(4-vinyl benzyl alcohol) nanocomposite has a refractive index of 1.73 and excellent transparency (>85% from 500 nm to 800 nm). The refractive index of the nanocomposite can be further increased to 1.77 by replacing aliphatic acetic acid modified TiO2 with aromatic phenyl acetic acid modified TiO2. The results of this work provide new knowledge and a new pathway to design a polymer based high refractive index material.

Enhancing performance of P3HT:TiO2 solar cells using doped and surface modified TiO2 nanorods

Here we demonstrated an approach to increase performance of P3HT:TiO2 solar cell either by electron deficient boron or electron rich bismuth doping into TiO2 nanorods. The B doping increases the absorption, crystallinity and electron mobility of TiO2 nanorods. The Bi-doped TiO2 has higher J(sc) as compared with B-doped TiO2, mainly due to the improvement of electron density and increased absorption of TiO2 nanorods. The devices were fabricated from TiO2 nanorods being surface modified by organic dye W-4. The dye facilitates the bandgap alignment and compatibility between TiO2 and P3HT. The power conversion efficiency of solar cell has been increased by 1.33 times and 1.30 times for Bi-doped TiO2 and B-doped TiO2, respectively, as compared with that of as-synthesized TiO2. The results suggest the optical and electronic properties of TiO2 can be tuned by various dopants to enhance the device performance.

Low Pressure Radio-Frequency Oxygen Plasma Induced Oxidation of Titanium - Surface Characteristics and Biological Effects

Objective This research was designed to investigate the effects of low pressure radio-frequency (RF) oxygen plasma treatment (OPT) on the surface of commercially pure titanium (CP-Ti) and Ti6Al4V. Surface topography, elemental composition, water contact angle, cell viability, and cell morphology were surveyed to evaluate the biocompatibility of titanium samples with different lengths of OP treating time. Materials and Methods CP-Ti and Ti6Al4V discs were both classified into 4 groups: untreated, treated with OP generated by using oxygen (99.98%) for 5, 10, and 30 min, respectively. After OPT on CP-Ti and Ti6Al4V samples, scanning probe microscopy, X-ray photoelectron spectrometry (XPS), and contact angle tests were conducted to determine the surface topography, elemental composition and hydrophilicity, respectively. The change of surface morphology was further studied using sputtered titanium on silicon wafers. 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay and F-actin immunofluorescence stain were performed to investigate the viability and spreading behavior of cultivated MG-63 cells on the samples. Results The surface roughness was most prominent after 5 min OPT in both CP-Ti and Ti6Al4V, and the surface morphology of sputtered Ti sharpened after the 5 min treatment. From the XPS results, the intensity of Ti°, Ti2+, and Ti3+ of the samples’ surface decreased indicating the oxidation of titanium after OPT. The water contact angles of both CP-Ti and Ti6Al4V were increased after 5 min OPT. The results of MTT assay demonstrated MG-63 cells proliferated best on the 5 min OP treated titanium sample. The F-actin immunofluorescence stain revealed the cultivated cell number of 5 min treated CP-Ti/Ti6Al4V was greater than other groups and most of the cultivated cells were spindle-shaped. Conclusions Low pressure RF oxygen plasma modified both the composition and the morphology of titanium samples’ surface. The CP-Ti/Ti6Al4V treated with 5 min OPT displayed the roughest surface, sharpest surface profile and best biocompatibility.

Prenatal imaging and immunohistochemical analysis of congenital peribronchial myofibroblastic tumor

A 32-year-old pregnant woman, gravida 4 para 1, was referred to us at 27 weeks’ gestation because of fetal hydrops. Ultrasound examination revealed a male fetus with a large homogeneous mass occupying the whole mediastinum with encasement of the great vessels and bronchus (Figure 1 and Videoclip S1). The tumor had a spiculated margin and infiltrated deep into adjacent tissues, suggestive of a sarcoma or other malignancy (Videoclip S2). Subsequent karyotyping following amniocentesis provided a normal result. Maternal blood tests were negative for active infection of adenovirus, toxoplasma and cytomegalovirus. Fetal magnetic resonance imaging revealed a large mediastinal tumor of 6 cm in longitudinal diameter with encasement of adjacent mediastinal structures (Figure 2). At 29 weeks’ gestation, the neonate was delivered by elective Cesarean section and intubated by ex-utero intrapartum treatment owing to fetal distress. Apgar scores were 0, 1 and 4 at 1, 5 and 10 min, respectively. The newborn was put on immediate ventilator support for severe hypoxemia, and bilateral chest tubes were inserted to drain the pleural effusions. Transthoracic sonography showed a large extracardiac mediastinal mass with compression of the left atrium. Despite the advanced medical support, the newborn developed refractory hypotension and died 2 days later. Autopsy revealed multiple cystic changes in the periventricular area of the brain (Figure S1). The mediastinal tumor was brown and soft and weighed 26.2 g with dimensions of 69 × 37 mm (Figure 3). It was found to encompass the esophagus, trachea, pulmonary trunk, aortic arch and other great vessels. Microscopic examination of the mass revealed interlacing fascicles of uniform spindle cells, with focal nuclear atypia (Figure S2). These tumor cells were diffusely positive for vimentin, focally positive for smooth muscle actin and CD68, but negative for CD31, CD34, S-100 and desmin. Tumor complementary DNA of the fusion gene transcript ETV6-NTRK3 was amplified specifically and no specific fusion gene transcripts were detected. Fluorescence in-situ hybridization revealed a wild-type EWSR1, encoding the Ewing sarcoma fusion protein, with no splitting of the alleles. The diagnosis of congenital peribronchial myofibroblastic tumor (CPMT) was made based on the myofibroblastic immunophenotype and genetic investigations (Table 1 and Table S1)1–3. CPMT was first defined in 1993 by McGinnis et al.4 to describe a neoplasm that develops from the Figure 1 Axial (a) and longitudinal (b) ultrasound images of thoracic cage of a fetus with congenital peribronchial myofibroblastic tumor, showing pleural effusion ( ) and a solid lobulated mediastinal mass (M) (6.05 × 1.91 cm) extending from neck to diaphragm with encasement of trachea (b; arrow) and compression of bilateral atria. Arrows in (a) identify multiple spiculations of the tumor with extension into adjacent lung tissue. H, heart.

BiFeO3/YSZ bilayer electrolyte for low temperature solid oxide fuel cell

We have demonstrated BiFeO3 (BFO) as a potential bilayer electrolyte for 650 °C low temperature solid oxide fuel cell application. The stoichiometric perovskite BFO is synthesized by wet chemistry, calcined at 500 °C and sintered at 850 °C. The crystalline structure is confirmed by X-ray diffraction spectroscopy, the atomic ratios (Bi : Fe) of 1.02 and 1.00 are determined by X-ray energy dispersive spectroscopy and inductively coupled plasma-mass spectroscopy, respectively. The X-ray photoelectron spectroscopy analysis indicates the presence of oxygen vacancies which can partially reduce Fe3+ and result in relatively high dielectric constant (6252 at 100 kHz) and ionic conductivity (>10−2 S cm−1 at 650 °C). The BFO is coated with an yttria-stabilized zirconia (YSZ) protective layer to avoid hydrogen reduction of BFO. This bilayer electrolyte exhibits a 1.6 times increase in maximum power density as compared with pure YSZ when a Ni–YSZ anode and lanthanum strontium cobalt ferrite (LSCF) cathode are used in the fuel cell at 650 °C.