Tzu-Chien Wei

Poly(N-vinyl-2-pyrrolidone)-capped platinum nanoclusters on indium-tin oxide glass as counterelectrode for dye-sensitized solar cells

Poly(N-vinyl-2-pyrrolidone)-capped platinum nanoclusters were deposited on indium tin oxide glass as a counterelectrode for dye-sensitized solar cells using a “two-step dip coating” process at room temperature. Compared to sputtered-Pt electrodes, an electrode produced by this technique exhibited ultralow Pt-loading at 4.89μg∕cm2 and an acceptable charge-transfer resistance of 5.66Ωcm2. Current-voltage characteristics of the DSSC at this stage stand at 0.66V on VOC, 10.5mA∕cm2 on ISC, 0.41 on fill factor, and 2.84% cell efficiency under AM1.5, 100mW∕cm2 illumination.

Platinum/titanium bilayer deposited on polymer film as efficient counter electrodes for plastic dye-sensitized solar cells

A surface-rich platinum/titanium bilayer was deposited on poly(ethylene naphthalate) film by vacuum sputtering as counterelectrode for plastic dye-sensitized solar cells (DSSCs). Compared to the electrodes made of pure Pt layer, this electrode maintained similar electrochemical catalytic effect at relative low Pt usage. Current-voltage characteristics of the plastic DSSC at this stage stand at 0.69V on VOC, 9.97mA∕cm2 on ISC, 0.69 on fill factor, and 4.31% cell efficiency under AM1.5, 100mW∕cm2 illumination.

High Electrocatalytic and Wettable Nitrogen-Doped Microwave-Exfoliated Graphene Nanosheets as Counter Electrode for Dye-Sensitized Solar Cells

In this paper, high electrocatalytic and wettable nitrogen-doped microwave-exfoliated graphene (N-MEG) nanosheets are used as Pt-free counter electrode (CE) for dye-sensitized solar cells (DSSCs). A low cost solution-based process is developed by using cyanamide (NH2 CN) at room temperature and normal pressure. The pyrrolic and pyridinic N atoms are doped into the carbon conjugated lattice to enhance electrocatalytic activity. N-MEG film having N-doping active sites and large porosity provides a wettable surface to facilitate electrolyte diffusion so that improves fill factor. Moreover, the control of the air exposure time after completing N-MEG film is found to be crucial to obtain a reliable N-MEG CE. A high DSSC efficiency up to 7.18% can be achieved based on N-MEG CE, which is nearly comparable to conventional Pt CE.

Electrodeposited Ultrathin TiO2 Blocking Layers for Efficient Perovskite Solar Cells

In this study, the electrodeposition (ED) of ultrathin, compact TiO2 blocking layers (BLs) on fluorine-doped tin oxide (FTO) glass for perovskite solar cells (PSCs) is evaluated. This bottom-up method allows for controlling the morphology and thickness of TiO2 films by simply manipulating deposition conditions. Compared with BLs produced using the spin-coating (SC) method, BLs produced using ED exhibit satisfactory surface coverage, even with a film thickness of 29 nm. Evidence from cyclic voltammetry shows that an ED BL suppresses interfacial recombination more profoundly than an SC BL does, consequently improving the photovoltaic properties of the PSC significantly. A PSC equipped with an ED TiO2 BL having a 13.6% power conversion efficiency is demonstrated.

Plastic based dye-sensitized solar cells using Co9S8 acicular nanotube arrays as the counter electrode

Novel one-dimensional (1D) Co9S8 acicular nanotube arrays (ANTAs) are fabricated on a conducting plastic substrate by a two-step approach. Layered cobalt carbonate hydroxide (Co(CO3)0.5(OH)x·11H2O, LCCH) acicular nanorod arrays (ANRAs) are fabricated on a conducting plastic substrate by chemical bath deposition (CBD), followed by a simple ionic-exchange process to convert the LCCH ANRAs into Co9S8 ANTAs. The compositions of the films are verified by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS) mapping; their morphologies are examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The films of Co9S8 ANTAs, obtained after various periods of the CBD, are analyzed by cyclic voltammetry (CV) measurements and Tafel polarization curves, and the Co9S8 ANTAs obtained from 150 min of CBD show higher electrocatalytic ability towards the I−/I3− reaction than sputtered Pt. In addition, the long-term stability of the Co9S8 ANTAs film in I−/I3− electrolyte was tested by CV. The plastic based Co9S8 ANTAs electrodes are used as the counter electrodes (CEs) of flexible dye-sensitized solar cells (DSSCs), and a high power conversion efficiency of 5.47% is achieved, which is comparable to that of the DSSC using sputtered Pt (5.62%). Therefore, the Co9S8 ANTAs are proposed to be a reliable material to replace Pt as plastic based CEs of DSSCs.

Electroless Platinum Counter Electrode for Dye-Sensitized Solar Cells by Using Self-Assembly Monolayer Modification

In this study, a cost-effective and low temperature wet process has been developed for the fabrication of a Pt counter electrode in dye-sensitized solar cells (DSSCs) with superior coating selectivity by means of self-assembly monolayer modification and electroless deposition. Using such Pt counter electrode prepared by our method, it is easy to deposit a Pt thin film under ambient atmosphere and low temperature without a high vacuum chamber and the acceptable charge-transfer resistance of 1.24 Ω cm 2 is obtained. Moreover, the DSSC exhibited improved performance compared to the DSSC with a sputtered Pt counter electrode.

Crystal Growth and Dissolution of Methylammonium Lead Iodide Perovskite in Sequential Deposition: Correlation between Morphology Evolution and Photovoltaic Performance

Crystal morphology and structure are important for improving the organic-inorganic lead halide perovskite semiconductor property in optoelectronic, electronic, and photovoltaic devices. In particular, crystal growth and dissolution are two major phenomena in determining the morphology of methylammonium lead iodide perovskite in the sequential deposition method for fabricating a perovskite solar cell. In this report, the effect of immersion time in the second step, i.e., methlyammonium iodide immersion in the morphological, structural, optical, and photovoltaic evolution, is extensively investigated. Supported by experimental evidence, a five-staged, time-dependent evolution of the morphology of methylammonium lead iodide perovskite crystals is established and is well connected to the photovoltaic performance. This result is beneficial for engineering optimal time for methylammonium iodide immersion and converging the solar cell performance in the sequential deposition route. Meanwhile, our result suggests that large, well-faceted methylammonium lead iodide perovskite single crystal may be incubated by solution process. This offers a low cost route for synthesizing perovskite single crystal.

Direct Electroplated Metallization on Indium Tin Oxide Plastic Substrate

Looking foward to the future where the device becomes flexible and rollable, indium tin oxide (ITO) fabricated on the plastic substrate becomes indispensable. Metallization on the ITO plastic substrate is an essential and required process. Electroplating is a cost-effective and high-throughput metallization process; however, the poor surface coverage and interfacial adhesion between electroplated metal and ITO plastic substrate limits its applications. This paper develops a new method to directly electroplate metals having strong adhesion and uniform deposition on an ITO plastic substrate by using a combination of 3-mercaptopropyl-trimethoxysilane (MPS) self-assembled monolayers (SAMs) and a sweeping potential technique. An impedance capacitive analysis supports the proposed bridging link model for MPS SAMs at the interface between the ITO and the electrolyte.

Recent Development of Graphene-Based Cathode Materials for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) have attracted extensive attention for serving as potential low-cost alternatives to silicon-based solar cells. As a vital role of a typical DSSC, the counter electrode (CE) is generally employed to collect electrons via the external circuit and speed up the reduction reaction of I3- to I- in the redox electrolyte. The noble Pt is usually deposited on a conductive glass substrate as CE material due to its excellent electrical conductivity, electrocatalytic activity, and electrochemical stability. To achieve cost-efficient DSSCs, reasonable efforts have been made to explore Pt-free alternatives. Recently, the graphene-based CEs have been intensively investigated to replace the high-cost noble Pt CE. In this paper, we provided an overview of studies on the electrochemical and photovoltaic characteristics of graphene-based CEs, including graphene, graphene/Pt, graphene/carbon materials, graphene/conducting polymers, and graphene/inorganic compounds. We also summarize the design and advantages of each graphene-based material and provide the possible directions for designing new graphene-based catalysts in future research for high-performance and low-cost DSSCs.

Pyrazine-incorporating panchromatic sensitizers for dye sensitized solar cells under one sun and dim light

New D–A′–π–A type (D = electron donor, A′ = auxiliary acceptor, π = π-conjugated bridge, and A = electron acceptor/anchor) sensitizers with two bis(alkoxy)phenyl substituents incorporating thieno[3,4-b]pyrazines (TP) or a benzo[3,4-b]pyrazine (BP) entity as the auxiliary acceptor have been synthesized for application in dye-sensitized solar cells (DSSCs). Under 1 sun illumination, the DSSCs fabricated from the two BP dyes with a co-adsorbent have efficiencies of 8.39% and 9.03%, respectively. The latter surpasses that of the standard N719 dye (8.87%). Under dim light conditions MD7 exhibited a power conversion efficiency of 18.95% and 27.17% under 300 lux and 6000 lux irradiance, respectively.