Kuan-Chieh Huang

CoS Acicular Nanorod Arrays for the Counter Electrode of an Efficient Dye-Sensitized Solar Cell

One-dimensional cobalt sulfide (CoS) acicular nanorod arrays (ANRAs) were obtained on a fluorine-doped tin oxide (FTO) substrate by a two-step approach. First, Co(3)O(4) ANRAs were synthesized, and then they were converted to CoS ANRAs for various periods. The compositions of the films obtained after various conversion periods were verified by X-ray diffraction, UV-visible spectrophotometry, and X-ray photoelectron spectroscopy; their morphologies were examined at different periods by scanning electron microscopic and transmission electron microscopic images. Electrocatalytic abilities of the films toward I(-)/I(3)(-) were verified through cyclic voltammetry (CV) and Tafel polarization curves. Long-term stability of the films in I(-)/I(3)(-) electrolyte was studied by CV. The FTO substrates with CoS ANRAs were used as the counter electrodes for dye-sensitized solar cells; a maximum power conversion efficiency of 7.67% was achieved for a cell with CoS ANRAs, under 100 mW/cm(2), which is nearly the same as that of a cell with a sputtered Pt counter electrode (7.70%). Electrochemical impedance spectroscopy was used to substantiate the photovoltaic parameters.

A high performance dye-sensitized solar cell with a novel nanocomposite film of PtNP/MWCNT on the counter electrode

An imide-functionalized material, poly(oxyethylene)-segmented polymer, was synthesized from the reaction of poly(oxyethylene)diamine of 2000 g mol−1Mw and 4,4′-oxydiphthalic anhydride and used to disperse hybrid nanomaterials of platinum nanoparticles and multi-wall carbon nanotubes (PtNP/MWCNT). The composite material was spin-coated into film and further prepared as the counter electrode (PtNP/MWCNT-CE) for a dye-sensitized solar cell (DSSC). The short-circuit current density (JSC) and power-conversion efficiency (η) of the DSSC with PtNP/MWCNT-CE were found to be 18.01 ± 0.91 mA cm−2 and 8.00 ± 0.23%, respectively, while the corresponding values were 14.62 ± 0.19 mA cm−2 and 6.92 ± 0.07% for a DSSC with a bare platinum counter electrode (Pt-CE). The presence and distribution of PtNP/MWCNT on the CE were characterized by using scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The attachment of PtNPs on MWCNTs was observed by transmission electron microscopy (TEM). Cyclic voltammetry (CV), incident-photo-to-current efficiency (IPCE) and electrochemical impedance spectra (EIS) were correlated to explain the efficacy of this nanocomposite system.

Facile fabrication of PtNP/MWCNT nanohybrid films for flexible counter electrode in dye-sensitized solar cells

A platinum nanoparticle/multi-wall carbon nanotube (PtNP/MWCNT) hybrid counter electrode (CE) based on a flexible substrate, Ti foil, was prepared for a high performance dye-sensitized solar cell (DSSC) via a facile fabricating route. This flexible nanohybrid CE was established by using a requisite homemade dispersant, consisting of poly(oxyethylene) segment and imide linkage functionalities. MWCNTs were well suspended in an ethanol/water solution in the presence of copolymer dispersant and PtNPs. The solution containing the PtNP/MWCNT (2/1 weight ratio) hybrid was further coated into a thin film on the Ti foil by the doctor blade technique, followed by annealing at 390 °C to obtain the flexible PtNP/MWCNT hybrid CE. The solar-to-electricity conversion efficiency (η) of a DSSC with the flexible PtNP/MWCNT hybrid CE gave a higher value of 9.04% in comparison to that of the cell with a conventional Pt CE (η = 7.47%). A rougher surface morphology of the nanohybrid film precisely controlled by the configuration of MWCNT was obtained, with reference to that of a Pt-sputtered film. The PtNP/MWCNT hybrid film was physically characterized by scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. Cyclic voltammetry, incident-photon-to-current efficiency, and electrochemical impedance spectra were examined for confirming the high electro-catalytic ability of this flexible PtNP/MWCNT hybrid CE.

A counter electrode based on hollow spherical particles of polyaniline for a dye-sensitized solar cell

Hollow spherical polyaniline (hsPANI) particles are synthesized and deposited on an ITO/glass substrate to prepare a counter electrode (designated as hsPANI-CE) for a dye-sensitized solar cell (DSSC). The structure and crystallization of the hsPANI particles are characterized by using high resolution transmission electron microscopy (HR-TEM), field-emission scanning electron microscopy (FE-SEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectra. A power-conversion efficiency (η) of 6.84% is obtained for the DSSC with the hsPANI-CE, while it is 6.02% in the case of the DSSC with a CE based on pristine PANI (designated as PANI-CE). Such enhancement is attributed to the hsPANI film having a larger active surface area (A) of 0.191 cm2, compared to that of the PANI film (A = 0.126 cm2), both values being estimated by a rotating disk electrode (RDE). Cyclic voltammetric (CV) curves have evidenced that the electro-catalytic ability of the hsPANI-CE for the reduction of tri-iodide (I3−) ions is higher than that of the PANI-CE. As a reference, the DSSC with a Pt-sputtered CE gives an η of 7.17%. Electrochemical impedance spectroscopic (EIS) spectra are used to substantiate the photovoltaic behaviors. The results suggest that the film consisting of hsPANI particles can be a potential catalytic layer for the replacement of Pt in the CE of a DSSC.

Polymer-dispersed MWCNT gel electrolytes for high performance of dye-sensitized solar cells

A hybrid of polymer-dispersed multi-walled carbon nanotubes (MWCNT) was utilized in networking with the conventional composition of gel electrolyte in dye-sensitized solar cells (DSSCs) to purposely enhance the cell efficiency. The requisite polymer as the dispersant is structurally tailored for its functionalities consisting of poly(oxyethylene)-segmented amides and imides. The existence of the dispersant is multi-functional for first de-bundling the originally aggregated MWCNT and subsequently networking with the conventional gel electrolyte, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP)/LiI system. The gel electrolyte comprised of only 0.25 wt% MWCNT/POEM in the finely dispersed state was fabricated into a quasi-solid-state DSSC which showed high power-conversion efficiency (η) of 6.86% and short-circuit current density (JSC) of 15.3 mA cm−2 at the test of 100 mW cm−2 irradiation. The DSSC efficiency was significantly improved from the use of the unmodified gel electrolyte having the values of JSC = 9.6 mA cm−2 and η = 4.63%. The enhancement was further confirmed by the electrochemical impedance spectra analyses for the lowest Warburg resistance (Rw). The fine dispersion of MWCNT in the polymeric dispersant was characterized by UV-Vis, TEM, FT-IR and DSC. The finding indicates the role of MWCNT for homogenizing the amorphous PVDF–HFP and facilitating the diffusion state of I−/I3− ion pairs in this electrolyte system.

Using a low temperature crystallization process to prepare anatase TiO2 buffer layers for air-stable inverted polymer solar cells

In this study, we fabricated inverted polymer solar cells featuring titanium dioxide (TiO2) as the electron collection layer and vanadium (V) oxide (V2O5) as the hole collection layer. TiO2 films (anatase phase) were prepared by combining electrochemical deposition with high-pressure crystallization. The low temperature process used to obtain the TiO2 films minimized interdiffusion of Ti and In species between the TiO2 and ITO films and maintained the conductivity of the indium tin oxide substrate. The inverted device reached a power conversion efficiency of 3.22% and exhibited much better stability under ambient conditions relative to that of the corresponding conventional device.

Controlling Formation of Silver/Carbon Nanotube Networks for Highly Conductive Film Surface

Flexible polymer films with high electrical conductivity were prepared through a simple coating of well-dispersed silver nanoparticle (AgNP) and multiwalled carbon nanotube (CNT) solution. The hybrid film with surface resistance as low as 1 × 10(-2) Ω/sq was prepared by controlling the annealing temperature in air and by using a suitable composition of silver nitrate/CNT/poly(oxyethylene)-oligo(imide) (POE-imide) in the ratio 20:1:20 by weight. During the heating, color of the film surface changed from black to golden to milky white, indicating the accumulation of AgNPs through surface migration and melting into CNT-connected networks. Thermogravimetric measurements showed that the transition temperature of 170 °C was responsible for the POE-imide degeneration and the subsequent Ag melting with a decrease in the surface resistance from 2.1 × 10(5) to 2.0 × 10(-1) Ω/sq, which was able to illuminate light-emitting diode lamps because of the formation of a continuous Ag network.

Improved exchange reaction in an ionic liquid electrolyte of a quasi-solid-state dye-sensitized solar cell by using 15-crown-5-functionalized MWCNT

Nanocomposite, 15-crown-5-functionalized multi-wall carbon nanotubes (denoted as MWCNT-15-C-5) were synthesized and used as an additive along with the ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) in the electrolyte of a dye-sensitized solar cell (DSSC); the pertinent quasi-solid-state DSSC showed a far superior photovoltaic performance than that of a cell with bare EMIBF4 or with MWCNT-added EMIBF4 (MWCNT/EMIBF4). The heterocyclic structure of the crown ether, 15-C-5, provides its cavities to capture the lithium ions (Li+) in a DSSC, thereby facilitating the dissolution of Li+ and I− in the electrolyte of the cell. This further contributes to an improvement in the exchange reaction of I−/I3− in the electrolyte with EMIBF4. Consequently, the values of short-circuit current density (JSC) and power-conversion efficiency (η) of the DSSC with both EMIBF4 and MWCNT-15-C-5 in its electrolyte showed an increase from 3.23 ± 0.30 to 5.53 ± 0.38 mA cm−2 and from 1.52 ± 0.04 to 2.11 ± 0.10%, respectively, with reference to the values of a DSSC with bare EMIBF4. Moreover, the at-rest durability of this quasi-solid-state DSSC was found to be unfailing for a period of 1200 h at 100 mW cm−2 illumination. Explanations are substantiated with Raman spectra, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HR-TEM), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS).

A dual-functional Pt/CNT TCO-free counter electrode for dye-sensitized solar cell

A nanohybrid of platinum and carbon nanotubes (Pt/CNT) with dual functions of catalytic activity and conductivity was synthesized. The selection of the poly(oxyethylene)-backboned polyimide dispersant was essential for preparing the dispersion with the de-bundled CNTs and platinum salts in ethanol/water. Subsequent solution casting and annealing at the optimized temperature of 390 °C led to the in situ reduction of platinum salts and the formation of a thin film of Pt/CNT nanohybrids on the glass substrate. The film was used directly as the counter electrode (CE) in a dye-sensitized solar cell (DSSC), which exhibited a short-circuit current density of 16.6 ± 0.2 mA cm−2 and a power conversion efficiency of 6.96 ± 0.09% at 100 mW cm−2 illumination. This performance is comparable with a DSSC with a conventional Pt-CE, and feasible for replacing the conventional transparent conductive oxide (TCO) conductive layer in DSSCs.

Au and Pd embrittlement in space-confined soldering reactions for 3D IC applications

Soldering reactions under space confinement has become increasingly important due to its application for chip stacking in three-dimensional integrated circuits (3D ICs. This study reports the effects of Au, from the dissolution of surface finishes, in such space-confined solder joints. Our results indicate that (Au,Ni)Sn4 can form a continuous layer across the entire of the joint, even when Au is very thin. This morphology is detrimental to the joint reliability. In other words, the so-called gold embrittlement has becomes relevant in 3D IC packaging. Pd is one of the most commonly used materials for surface finishes. The effects of Pd will also be discussed. In addition, solutions to solve the Au and Pd embrittlement are presented in this work.