A Perovskite Photovoltaic Mini-Module-CsPbBr3 Photoelectrochemical Cell Tandem Device for Solar-Driven Degradation of Organic Compounds.

Recently, halide perovskites have been widely explored for high-efficiency photocatalysis or photoelectrochemical (PEC) cells. Here, in order to make an efficient photoanode electrode for the degradation of pollutants, concretely 2-mercaptobenzothiazole (MBT), nanoscale cesium lead bromide (CsPbBr3) perovskite was directly formed on the surface of mesoporous titanium dioxide (meso-TiO2) film using a two-step spin-coating process. This photoelectrode recorded a photocurrent of up to 3.02 ± 0.03 mA/cm2 under standard AM 1.5G (100 mW/cm2) illumination through an optimization process such as introducing a thin aluminum oxide (Al2O3) coating layer. Furthermore, to supply high voltage for efficient oxidation of MBT without an external bias, we developed a new photovoltaic/PEC tandem system using a methylammonium lead iodide (MAPbI3) based mini-module consisting of three solar cells interconnected in series and confirmed its successful operation. This approach looks very promising due to its applicability to various PEC reactions.

Adsorption and Cation-Exchange Behavior of Zinc Sulfide on Mesoporous TiO2 Film and Its Applications to Solar Cells.

Zinc sulfide (ZnS) was deposited onto the surface of mesoporous TiO2 film by a typical successive ionic layer adsorption and reaction (SILAR) process. By inducing a spontaneous cation exchange between ZnS and a target cation (Pb2+, Cu2+, Ag+, or Bi3+) dissolved in a chemical bath when they are in contact, it was demonstrated successfully that white translucent ZnS on the substrate could be changed to new brown-colored metal chalcogenides and the amount of ZnS deposited originally by different conditions could be compared in a qualitative way with the degree of color change. By utilizing this simple but effective process, the evolution of a well-known ZnS passivation layer prepared from different chemical baths in quantum dot (QD)-sensitized solar cells could be tracked visually by checking the degree of color change of TiO2/ZnS electrodes after the induced specific cation exchange. When applied to representative CdS QD-sensitized solar cells, it was revealed clearly how the different degrees and rates of ZnS deposition could affect the overall power conversion efficiency while finding an optimized passivation layer over TiO2/CdS electrode. An acetate anion-coupled Zn2+ source was observed to give a much faster deposition of a ZnS passivation layer than a nitrate anion one because of its higher pH-induced more-favorable adsorption of Zn2+ on the surface of TiO2. As another useful application of the ZnS-based cation exchange, as-deposited ZnS was used as a template for preparing a more complex metal chalcogenide onto a mesoporous TiO2 film. The ZnS-derived Sb2S3-sensitized electrode showed a promising initial result of over 1.0% overall power conversion efficiency with a very thin ZrO2 passivation layer between TiO2 and Sb2S3.

Nanoscale Perovskite-Sensitized Solar Cell Revisited: Dye-Cell or Perovskite-Cell?

A general and straightforward way of preparing few-nanometer-sized well-separated MAPbIx Br3-x (MA=methylammonium) perovskite photosensitizers on the surface of an approximately 1 µm thick mesoporous TiO2 photoanode was suggested through a two-step sequential deposition of low-concentrated lead halides (0.10-0.30 m PbI2 or PbBr2 ) and methylammonium iodide/bromide (MAI/MABr). When those nanoscale MAPbIx Br3-x perovskites were incorporated as a photosensitizer in typical solid-state dye-sensitized solar cells (ss-DSSCs), it could be verified clearly by the capacitance analysis that nano-particulate MAPbI3 perovskites play the same role as that of a typical dye sensitizer (MK-2 molecule) although their size, composition, and structure are different.

Efficient Planar Perovskite Solar Cells Using Passivated Tin Oxide as an Electron Transport Layer.

Planar perovskite solar cells using low-temperature atomic layer deposition (ALD) of the SnO2 electron transporting layer (ETL), with excellent electron extraction and hole-blocking ability, offer significant advantages compared with high-temperature deposition methods. The optical, chemical, and electrical properties of the ALD SnO2 layer and its influence on the device performance are investigated. It is found that surface passivation of SnO2 is essential to reduce charge recombination at the perovskite and ETL interface and show that the fabricated planar perovskite solar cells exhibit high reproducibility, stability, and power conversion efficiency of 20%.

CuS/CdS Quantum Dot Composite Sensitizer and Its Applications to Various TiO2 Mesoporous Film-Based Solar Cell Devices.

A nanoscale composite sensitizer composed of CuS and CdS quantum dots (QDs) was prepared by a simple but effective layer-by-layer reaction between a metal cation (Cu(2+) or Cd(2+)) and a sulfide anion (S(2-)). The as-prepared composite CuS/CdS QD sensitizer displayed an enhanced photon-to-current conversion over the sensitizing range of the visible spectrum compared to the counterpart of the pure CdS sensitizer. At the optimized ratio of the deposited amounts of CuS and CdS, the best CuS/CdS-sensitized mesoporous TiO2 cell with a polysulfide electrolyte showed an overall power conversion efficiency of 3.60% with a short circuit current (Jsc) of 11.77 mA/cm(2), an open circuit voltage (Voc) of 0.65 V, and a fill factor (FF) of 0.47. From the transmission electron microscopy images, the initially deposited CuS seemed to take a nucleation site to accumulate more CdS in the later deposition. The kinetic studies by impedance and Voc decay measurements also revealed that the CuS/CdS and CdS QD sensitizers made a similar interface between TiO2 and the electrolyte, but the former had a larger resistance of charge transfer with a longer lifetime of excitons after light absorption than the latter. To enhance the sensitizing power further, a multilayer QD sensitizer of CuS/CdS/CdSe was prepared by successive ionic layer adsorption and reaction (SILAR). This led to the best performance of 4.32% overall power conversion efficiency. Finally, a hybrid sensitizing system of inorganic QD (CuS/CdS) and organic dye (coded MK-2) was tested with a [Co(bpy)3](2+/3+) redox mediator. The CuS/CdS/MK-2 dye-sensitized cell showed over 3.0% efficiency under the standard illumination condition (1 sun).

Preparation of sildenafil citrate microcapsules and in vitro/in vivo evaluation of taste masking efficiency.

The aim of the present study was to prepare the particulate taste-masking system to mask the bitter taste of sildenafil citrate (SC), a well-known phosphodiesterase-5 inhibitor used for erectile dysfunction (ED) and pulmonary artery hypertension (PAH). It was evaluated for the taste masking efficiency by the in vitro measurement using electronic tongue (e-tongue) system and the in vivo human panel sensory test. Microcapsules were prepared by microencapsulation with a gastro-soluble polymer, Eudragit(®) E100 (E100), using a spray drying technique at four different weight ratios (2:1, 1:1, 1:2, and 1:3). Characters of prepared microcapsules and the effect of polymer ratio on the taste masking were investigated. The particle morphology and the distribution of SC in microcapsules were observed by SEM-EDS and physical properties were evaluated by PXRD, Raman spectroscopy, and DSC. By drug dissolution studies at pH 1.2 buffer and DW, it was found that E100 was not able to alter the drug release in stomach. As the result of taste evaluation studies, there were a good correlation (R(2)=0.9867) between the weight ratio of polymer and the taste masking efficiency expressed in the distances on the PCA map of the e-tongue data, and a relevance of the e-tongue measurement with the result of sensory test.

Layer-by-layer-assembled quantum dot multilayer sensitizers: how the number of layers affects the photovoltaic properties of one-dimensional ZnO nanowire electrodes.

Layer cake: Multilayered CdSe quantum dot (QD) sensitizers are layer-by-layer assembled onto ZnO nanowires by making use of electrostatic interactions to study the effect of the layer number on the photovoltaic properties. The photovoltaic performance of QD-sensitized solar cells critically depends on this number as a result of the balance between light-harvesting efficiency and carrier-recombination probability.

Preparation of multilayered CdSe quantum dot sensitizers by electrostatic layer-by-layer assembly and a series of post-treatments toward efficient quantum dot-sensitized mesoporous TiO2 solar cells.

A multilayer of CdSe quantum dots (QDs) was prepared on the mesoporous surface of a nanoparticulate TiO(2) film by a layer-by-layer (LBL) assembly using the electrostatic interaction of the oppositely charged QD surface for application as a sensitizer in QD-sensitized TiO(2) solar cells. To maximize the absorption of incident light and the generation of excitons by CdSe QDs within a fixed thickness of TiO(2) film, the experimental conditions of QD deposition were optimized by controlling the concentration of salt added into the QD-dissolved solutions and repeating the LBL deposition a few times. A proper concentration of salt was found to be critical in providing a deep penetration of QDs into the mesopore, thus leading to a dense and uniform distribution throughout the whole TiO(2) matrix while anchoring the oppositely charged QDs alternately in a controllable way. A series of post-treatments with (1) CdCl(2), (2) thermal annealing, and (3) ZnS-coating was found to be very critical in improving the overall photovoltaic properties, presumably through a better connection between QDs, effective passivation of QD's surface, and a high impedance of recombination, which were proved by transmission electron microscopy (TEM) and electrochemical impedance spectroscopy (EIS) experiments. With a proper post-treatment of multilayered QDs as a sensitizer, the overall power conversion efficiency in the CdSe QD-sensitized TiO(2) solar cells could reach 1.9% under standard illumination condition of simulated AM 1.5G (100 mW/cm(2)).

Multifunctional conjugated polymers with main-chain donors and side-chain acceptors for dye sensitized solar cells (DSSCs) and organic photovoltaic cells (OPVs).

A novel multifunctional conjugated polymer (RCP-1) composed of an electron-donating backbone (carbazole) and an electron-accepting side chain (cyanoacetic acid) connected through conjugated vinylene and terthiophene has been synthesized and tested as a photosensitizer in two major molecule-based solar cells, namely dye sensitized solar cells (DSSCs) and organic photovoltaic cells (OPVs). Promising initial results on overall power conversion efficiencies of 4.11% and 1.04% are obtained from the basic structure of DSSCs and OPVs based on RCP-1, respectively. The well-defined donor (D)-acceptor (A) structure of RCP-1 has made it possible, for the first time, to reach over 4% of power conversion efficiency in DSSCs with an organic polymer sensitizer and good operation stability.

Reduced graphene oxide (rGO)-wrapped fullerene (C60) wires.

The assembly of reduced graphene oxide (rGO) and fullerene (C(60)) into hybrid (rGO/C(60)) wires was successfully performed by employing the liquid-liquid interfacial precipitation method. The rGO sheets spontaneously wrapped C(60) wires through the π-π interaction between rGO and C(60). Structural characterization of the rGO/C(60) wires was carried out by using UV/visible spectroscopy, scanning electron microscopy, and transmission electron microscopy. FET devices with rGO/C(60) wires were fabricated to investigate their electrical properties. The I(ds)-V(g) curves of the hybrid wires exhibited p-type semiconducting behavior both in vacuum and in air, indicating hole transport through rGO as a shell layer, whereas pure C(60) wires and rGO sheets showed n-type and ambipolar behaviors, respectively, under vacuum. Possible application of the fabricated wires, such as photovoltaic devices, was also demonstrated.

Novel quinoxaline-based organic sensitizers for dye-sensitized solar cells.

Novel quinoxaline-based organic sensitizers using vertical (RC-21) and horizontal (RC-22) conjugation between an electron-donating triphenylamine unit and electron-accepting quinoxaline unit have been synthesized and used for dye-sensitized solar cells (DSSCs), leading to the relatively high power conversion efficiencies of 3.30 and 5.56% for RC-21 and RC-22, respectively. This result indicates that the quinoxaline electron-accepting unit is quite a promising candidate in organic sensitizers.

CdSe quantum dot (QD) and molecular dye hybrid sensitizers for TiO2 mesoporous solar cells: working together with a common hole carrier of cobalt complexes.

Redox couples based on cobalt complexes were found to be effective in regenerating both inorganic CdSe quantum dot- and organic dye-sensitizers. The hybrid sensitizer composed of CdSe QD and ruthenium sensitizer (Z907Na) dye showed a maximum power conversion efficiency of 4.76% on using cobalt(o-phen)(3)(2+/3+) as a common redox mediator.

Electrochemistry of conductive polymers. 45. Nanoscale conductivity of PEDOT and PEDOT:PSS composite films studied by current-sensing AFM.

[Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)] (PEDOT:PSS, Baytron P) composite films were prepared under various conditions and their conductivities were studied by the current-sensing atomic force microscopy (CS-AFM) technique. Topographic and current images of pristine and additive-treated PEDOT:PSS as well as electrochemically synthesized PEDOT films were obtained in nanoscale using the CS-AFM. The as-prepared pristine PEDOT:PSS films showed a low population of conductive spots isolated by large insulating regions; both their population and the conductivities increased upon addition of a few additives to the PEDOT:PSS solution before spin-coating. From the current-voltage (I-V) traces recorded at a few representative spots of different electronic states, much improved pathways for charge percolation appeared to have been established in the additive-treated films. Electrochemically prepared PEDOT films showed much better electrical properties compared with spin-casted films of chemically prepared polymers. The conductivity of all these films was shown to be significantly enhanced by the electrochemical doping process.

Regenerative PbS and CdS quantum dot sensitized solar cells with a cobalt complex as hole mediator.

Metal sulfide (PbS and CdS) quantum dots (QDs) were prepared over mesoporous TiO2 films by improved successive ionic layer adsorption and reaction (SILAR) processes. The as-prepared QD-sensitized electrodes were combined with a cobalt complex redox couple [Co(o-phen)3]2+/3+ to make a regenerative liquid-type photovoltaic cell. The optimized PbS QD-sensitized solar cells exhibited promising incident photon-to-current conversion efficiency (IPCE) of over 50% and an overall conversion efficiency of 2% at 0.1 sun in a regenerative mode. The overall photovoltaic performance of the PbS QD-sensitized cells was observed to be dependent on the final turn of the SILAR process, giving a better result when the final deposition was Pb2+, not S2-. However, in the case of CdS QD-sensitized cells, S2- termination was better than that of Cd2+. The cobalt complex herein used as a regenerative redox couple was found to be more efficient in generating photocurrents from PbS QD cells than the typical hole scavenger Na2S in a three-electrode configuration. The CdS-sensitized cell with this redox mediator also showed better defined current-voltage curves and an IPCE reaching 40%.

Electrochemistry of conductive polymers 37. Nanoscale monitoring of electrical properties during electrochemical growth of polypyrrole and its aging.

Electrical and morphological properties of polypyrrole (PPy) films were studied during and after their electrochemical growth under various experimental conditions on a nanometer scale using a current-sensing atomic force microscope (CS-AFM). Of acetonitrile (ACN) solutions containing various amounts of water, one that contained 1.0% water produced the best quality films in their electrical and morphological properties in terms of homogeneities. The degree of doping, as well as time evolution of the film structure and its conductivity, of the PPy films was investigated during their growth in water and ACN with 1.0% water by obtaining the current images at a few designated growing stages, and the results were compared. Well-doped, conductive films were obtained from the very early stage during the electrodeposition of PPy in the ACN solution, while the films were poorly doped in water. As the film deposition progressed further in both aqueous and nonaqueous media, the doped areas spread over the whole surface leading to a more homogeneously conducting film. The current-voltage traces were obtained at each growing stage, which showed that the conductivity increases in both media as the PPy grows; the conductivity of the film grown in ACN is much higher than that of the film grown in water at all growing stages. The electrical properties of the PPy film deteriorated gradually upon exposure to air.