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CdS has been known to be one of the best junction partners for Cu(In,Ga)Se2 (CIGS) in CIGS solar cells. However, the use of thick CdS buffer decreases the short-circuit current density of CIGS solar cells. There are two obstacles that limit the use of ultrathin CdS. The first is plasma damage to CIGS during the preparation of transparent conducting windows and the second is a low shunt resistance due to the direct contact between the window and CIGS via pinholes in the thin CdS buffer. In other words, to avoid plasma damage and shunt paths, we may have to use a CdS buffer that is thicker than necessary to form a high-quality CdS/CIGS junction. This work aims to determine how thin the CdS buffer can be employed without sacrificing device performance while also eliminating the above two obstacles. We investigate the effect of CdS thickness on the performance of CIGS solar cells with silver nanowire-based window layers, which can eliminate both obstacles. An approximately 13 nm thick CdS buffer allows us to achieve high short-circuit current density and fill factor values. To attain an even high open-circuit voltage, an additional CdS buffer with a thickness of 13 nm is needed. The data from this study imply that an approximately 26 nm thick CdS buffer is sufficient to form a high-quality CdS/CIGS junction.

Optimally designed Si nanostructures can serve as effective light trapping structures for flexible crystalline ultrathin Si solar cells. In this study, we develop a unique quasi-hexagonal inverted nano-pyramid in a hexagonal array, fabricated by a combined process of nanosphere lithography and wet etching. Self-assembled silica nanoparticles were deposited on Si wafers by spin coating, followed by deposition of triangular metal nanodisks in a hexagonal array. The metal nanodisks were used as a wet etch mask in an alkaline solution to create the quasi-hexagonal Si nanostructures. We investigated a temporal evolution of the Si nanostructures with increasing the etch time to optimize optical performances. The newly developed nanostructures take a quasi-hexagonal inverted pyramid, which provides geometrically high compatibility with the self-assembled monolayers in a hexagonal array. We incorporated these quasi-hexagonal nanostructures to the flexible crystalline ultrathin Si solar cells, and the novel nanostructures exhibited optical performances comparable to conventional micro-pyramid textures while showing the enhanced mechanical flexibility of the ultrathin Si-based solar cells.

The effect of the temperature ramping rate of vapor transport deposition (VTD) on the morphology, crystallinity and orientation of SnS-absorber layers and their impact on SnS/CdS heterojunction thi...

The highest efficiency of 4.225% for vapor-transport-deposited (VTD) SnS absorber/CdS heterojunction solar cells with good long-term stability over two years is reported. These improved characteristics are attributed to the reduction in interface defects of the heterojunction, which can occur either during the deposition of transparent electrodes or direct annealing of the SnS/CdS heterojunction at 300 °C. The enhanced heterojunction interface quality is supported by the substantially reduced dark saturation current density and shunt conductance of the fabricated devices measured under dark conditions. Although the SnS/CdS device exhibits efficiency over 4%, significant short-circuit current loss mainly due to recombination was revealed by quantum efficiency and optical analysis. Admittance analysis shows the presence of numerous defect densities of Sn and S vacancies (>1017 cm−3) in the VTD-grown SnS absorber. Minimizing bulk and interface defect densities of SnS absorbers will be a key issue in achieving high efficiency (>5%) of SnS-based thin-film solar cells.

We report high efficiency cell processing technologies for the ultra-thin Si solar cells based on crystalline Si thin foils (below a 50 µm thickness) produced by the proton implant exfoliation (PIE) technique. Shallow textures of submicrometer scale is essential for effective light trapping in crystalline Si thin foil based solar cells. In this study, we report the fabrication process of random Si nanohole arrays of ellipsoids by a facile way using low melting point metal nanoparticles of indium which were vacuum-deposited and dewetted spontaneously at room temperature. Combination of dry and wet etch processes with indium nanoparticles as etch masks enables the fabrication of random Si nanohole arrays of an ellipsoidal shape. The optimized etching processes led to effective light trapping nanostructures comparable to conventional micro-pyramids. We also developed the laser fired contact (LFC) process especially suitable for crystalline Si thin foil based PERC solar cells. The laser processing parameters were optimized to obtain a shallow LFC contact in conjunction with a low contact resistance. Lastly, we applied the random Si nanohole arrays and the LFC process to the crystalline Si thin foils (a 48 µm thickness) produced by the PIE technique and achieved the best efficiency of 17.1% while the planar PERC solar cell without the Si nanohole arrays exhibit 15.6%. Also, we demonstrate the ultra-thin wafer is bendable to have a 16 mm critical bending radius.

We demonstrate the ability to fabricate high-quality nanoscale electrical contact between silver nanowires (AgNWs) and underlying semiconducting layers in chalcogenide thin film solar cells. AgNW electrodes have attracted many interests due to their ability for low temperature solution processing. However, they have a drawback that the interfacial defects can be generated between AgNWs and underlying rugged semiconductor layers making it difficult to form high-quality junction. To enhance the junction properties, conducting matrix layers have been adapted. Yet, the issues regarding the AgNW/semiconductor junction have not been fully resolved. We developed a facile method to form robust nanoscale contact between AgNWs and semiconducting thin films to achieve high performance chalcogenide thin film solar cells. The method is to deposit an ultra-thin semiconductor layer on devices using aqueous chemical bath deposition. The chemical bath deposition has capability to effectively fill even nanoscale gap and to form chemically stable bonds as well as an intimate junction. As a proof of concept, a CdS layer (~ 10 nm) was deposited using the chemical bath deposition on Cu(In,Ga)Se2 (CIGS) solar cells with a structure of AgNW/CdS/CIGS/Mo/Glass. We also identified that the key factor governing the current-voltage characteristic is the electrical contact between the AgNW electrode and the CdS buffer layer in CIGS thin film solar cells. The power conversion efficiency of the CIGS cell was dramatically improved from 4.9% to 14.2% owing to high-quality AgNW-CdS electrical contact produced by chemical bath deposition of the additional CdS layer as thin as 10 nm.

We quantitatively and analytically investigate the properties of buffer/window junctions and their effects on the energy band alignment and the current-voltage characteristics of Cu(In,Ga)Se2 (CIGS) thin film solar cells with solution processed silver nanowire (AgNW) composite window layers. AgNWs are generally embedded in a moderately conductive matrix layer to ensure lateral collection efficiency of charge carriers photogenerated in the lateral gaps present between AgNWs. Studies on the junctions between a buffer and AgNW-composite window layers and their effects on the performances of CIGS thin film solar cells have seldom been addressed. Here, we show that solution processed AgNW-composite window layers could induce defect states at the buffer/window interface, resulting in poor energy band alignment impeding carrier transport in the solar cells. On the basis of our analysis, we suggest an analytical expression of nmatrixDi2≥3.46×10−5e cm to avoid losses in the power conversion efficiency of the solar cells. nmatrix is the carrier concentration in a matrix layer embedding AgNWs, Di is the negative defect density at the buffer/window interface, and e is the relative dielectric constant of the matrix layer embedding AgNWs.

Noble metal-free mesoscopic perovskite solar cell based on low-cost molybdenum (Mo) cathode has been developed for the first time. By optimizing the thickness of Mo electrode and combination with high quality perovskite layer, the Mo cathode-based perovskite solar cell exhibited a best power conversion efficiency as high as 15.06% with invariance of current density–voltage curves at different scan rates and very small hysteresis according to scan direction. In addition to photovoltaic performances, importance of mechanical durability of a cathode material for perovskite solar cell was highlighted and results from nano-indentation and scratch test indicated that Mo electrode has superior resistance and restoration capability against external scratch or deformation compared to Au electrode. The Mo cathode-based perovskite solar cells have great potential for realizing low cost and high performance as well as mechanical durability.

Highly efficient planar perovskite optoelectronic devices are realized by amine-based solvent treatment on compact TiO2 and by optimizing the morphology of the perovskite layers. Amine-based solvent treatment between the TiO2 and the perovskite layers enhances electron injection and extraction and reduces the recombination of photogenerated charges at the interface.

The olivine Fe2GeS4 compound has attracted much attention as a thermodynamically stable derivative of pyrite FeS2, which has been studied extensively as an earth-abundant light-absorbing candidate material. Nevertheless, reports on nanocrystalline Fe2GeS4 and its optoelectronic properties are limited. Herein, Fe2GeS4 nanocrystals are synthesized via a solvent-free mechanochemical process. This process not only reduces the synthesis time, but also avoids the use of hazardous solvents, thereby mitigating environmental concerns. The crystallinity of the synthesized nanocrystals is significantly enhanced by a post-heat treatment in a sulfur-containing atmosphere, showing no phase decomposition. Lattice-resolved micrographs reveal that the post-annealed nanocrystals have a hexagonal-faceted platelet structure with (002) base planes. The oxide layer near the surface region is removed by the post-annealing process, most likely due to the replacement of oxygen with sulfur in the controlled atmosphere. The post-annealed Fe2GeS4 nanocrystals clearly exhibit an optical band gap of 1.43 eV and near-band-edge photoluminescent emission at 1.41 eV. This is the first experimental demonstration of the Fe2GeS4 nanocrystals having optoelectronic properties that are suitable for solar applications.

Preparation of well-interconnected TiO2 electrodes at low temperature is critical for the fabrication of highly efficient dye-sensitized solar cells (DSCs) on plastic substrates. Herein we explore a synergistic approach using a combination of chemical and physical sintering. We formulate a binder-free TiO2 paste based on “nanoglue” as the chemical sintering agent, and use it to construct a photoelectrode on plastic by low-temperature physical compression to further improve the connectivity of TiO2 films. We systematically investigated the factors affecting the photovoltaic performance and found the conditions to achieve electron diffusion lengths as long as 25 mm and charge collection efficiencies as high as 95%, as electrochemical impedance spectroscopy measurements indicate. We apply this approach to obtain a DSC deposited on plastic displaying 6.4% power conversion efficiency based on commercial P25 titania particles

We demonstrated the effect of the field dependency of charge carrier mobility on roll-off characteristic of current efficiency. Field dependent factor in Poole-Frenkel model is controlled to describe charge balance of electron and hole concentration at high field. It is well established that roll-off characteristic is dependent upon mobility match which results in charge balance in EML. We exhibited the improvement of the roll-off characteristic of current efficiency and explained how charge balance is induced through this description.

In this study, we demonstrated the effective morphological control of polymer:fullerene blends using three separate solvent systems: chloroform (CF), CF:1,8-diiodooctane (DIO), and CF:o-dichlorobenzene (ODCB). The polymer:fullerene blends are composed of two diketopyrrolopyrrole (DPP)-based polymers of P(DPP-alt-QT) and P(DPP-alt-DTBSe) and a fullerene derivative of [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM), i.e., P(DPP-alt-QT):PC71BM or P(DPP-alt-DTBSe):PC71BM. The CF:ODCB binary solvent exhibited the best photovoltaic performance among the three solvent systems for both polymer-based devices, although the CF:DIO also exhibited an improved performance compared to the CF system. By examining film morphology of the blend films, we found that the CF:ODCB enabled the most optimal nanoscale phase separation and the morphological features were strongly affected by the solubility of each material in the high boiling-point (BP) solvent. Specifically, the polymers have limited but slightly higher solubility in ODCB than in DIO, while the PC71BM molecules have a high solubility in both DIO and ODCB. Therefore, this work highlights that the optimally asymmetric solubility of each photoactive component in the high BP solvent is a critical factor to form the nanoscale, bicontinuous domains in the blend films and thereby to determine the performance of photovoltaic devices.

Highly efficient copper-zinc-tin-selenide (Cu2ZnSnSe4 ; CZTSe) thin-film solar cells are prepared via the electrodepostion technique. A metallic alloy precursor (CZT) film with a Cu-poor, Zn-rich composition is directly deposited from a single aqueous bath under a constant current, and the precursor film is converted to CZTSe by annealing under a Se atmosphere at temperatures ranging from 400 °C to 600 °C. The crystallization of CZTSe starts at 400 °C and is completed at 500 °C, while crystal growth continues at higher temperatures. Owing to compromises between enhanced crystallinity and poor physical properties, CZTSe thin films annealed at 550 °C exhibit the best and most-stable device performances, reaching up to 8.0 % active efficiency; among the highest efficiencies for CZTSe thin-film solar cells prepared by electrodeposition. Further analysis of the electronic properties and a comparison with another state-of-the-art device prepared from a hydrazine-based solution, suggests that the conversion efficiency can be further improved by optimizing parameters such as film thickness, antireflection coating, MoSe2 formation, and p-n junction properties.

We fabricated metallic Cu–Zn–Sn (CZT) precursor thin films via electrochemical deposition from aqueous metal salt solution on Mo-coated soda-lime glass substrates, and the influence of the subsequent sulfurization condition on the morphology, composition and structure of the final Cu2ZnSnS4 (CZTS) thin films was investigated. A rapid thermal annealing equipment was used for a systematic control of the sulfurization process parameters. The as-deposited films are composed of binary metallic alloys, which can be converted to the highly crystalline CZTS phase after sulfurization at temperatures above 500 °C. The composition of the CZT film barely changes during the sulfurization, and a small amount of CuS-based secondary phases exists even at 550 °C. However, a quick post-annealing KCN treatment effectively and selectively removes the secondary phase, evidenced by the Raman spectroscopy and elemental.

The open-circuit voltage of bulk heterojunction polymer solar cells utilizing 1,8-diiodooctane (DIO) as a processing additive was greatly improved by using an organic layer coated TiO 2 nanoparticle interfacial layer inserted between the active layer and the Al electrode. The transient photovoltage measurement revealed that there was significant non-geminate recombination at the DIO-processed active layer/Al electrode interface. Reduced open-circuit voltage ( V OC ) of the photovoltaic devices and high water contact angle of the DIO-processed active layer showed that the DIO-processed active layer has an undesirable surface composition for the electron collection. The organic layer coated TiO 2 nanoparticle interfacial layer effectively prevented the non-geminate recombination at the active layer/Al interface. As a result, we were able to significantly improve the V OC and power conversion efficiency from 0.46 V and 2.13% to 0.62 V and 3.95%, respectively.

We report a promising approach to fabricate organic–inorganic hybrid tandem photovoltaic devices with a reversed configuration. High bandgap hydrogenated amorphous silicon (a-Si:H) was deposited with plasma-enhanced chemical vapor deposition onto a solution-processed low bandgap organic photovoltaic (OPV) subcell. Two important factors for efficient tandem solar cells, interfacial series resistance (RS,int) and balanced photocurrents, were investigated. The intimate interfacial contact eliminated the RS,int, and sufficient transmittance of the OPV front subcell led to the well-balanced photocurrents. As a result, this reversed hybrid tandem device showed an enhanced efficiency of 3.3% and an open-circuit voltage of 1.51 V.

We designed and synthesized a new low band gap donor–acceptor copolymer (PDTDPP-Oct) composed of alternating dithieno[3,2- b :2′,3′- d ]thiophene and bis-thienyl-diketopyrrolo[3,4- c ]pyrrole units. The polymer films showed a very broad absorption band that extended up to 950 nm. Thermogravimetric analysis revealed good thermal stability and a high glass transition temperature of 128 °C. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the polymer were estimated to be −5.01 and −3.70 eV, respectively. Bulk heterojunction polymer solar cells were fabricated with the structure: ITO/PEDOT:PSS/polymer:PCBM/Al. The introduction of 1,8-octanedithiol as a processing additive to the polymer/PCBM blend solution significantly improved the device performance relative to devices prepared from the blend solution without the additive. This cell gave a short circuit current of −1.8 mA/cm 2 , an open circuit voltage of 0.60 V, and a fill factor of 0.52, yielding a power conversion efficiency of 0.55%. The performance improvements were mainly attributed to the fine morphology of the blend film.

Chalcopyrite CIS or CIGS have been regarded as promising absorbing materials for thin-film solar cells with widespread commercialization prospects. The most critical material properties of a CIS absorption layer that affect the overall PV performance include its microstructure and composition at a given bandgap energy. In this study, dense CISe films with high crystallinity and uniform, flat surfaces were fabricated on In2Se3/ITO employing single bath electrochemical deposition by adjusting the deposition parameters, such as the precursor concentration, pH, and applied potential. A simple formula is presented based on Faraday's law to quantitatively estimate the density of the electrodeposited thin films; from this, it was found that the as-deposited films had a very high relative density of 0.73. The high green density of the as-deposited film led to the full densification of the CISe film with ca. 10 μm sized grains. The binary selenide phase remaining in the sintered film was subsequently etched out using a KCN solution, resulting in an overall Cu-deficient composition in the film of [Cu]/[In] = 0.95.

Highlights: ► This work enhanced power conversion efficiency of the hybrid tandem solar cell from 1.0% to 2.6%. ► The interfacial series resistance of the tandem solar cell was eliminated by inserting ITO layer. ► This work shows the feasibility of the highly efficient hybrid tandem solar cells. -- Abstract: We demonstrate hybrid tandem photovoltaic devices with a transparent conductive interconnecting recombination layer. The series-connected hybrid tandem photovoltaic devices were developed by combining hydrogenated amorphous silicon (a-Si:H) and polymer-based organic photovoltaics (OPVs). In order to enhance the interfacial connection between the subcells, we employed highly transparent and conductive indium tin oxide (ITO) thin layer. By using the ITO interconnecting layer, the power conversion efficiency of the hybrid tandem solar cell was enhanced from 1.0% (V{sub OC} = 1.041 V, J{sub SC} = 2.97 mA/cm{sup 2}, FF = 32.3%) to 2.6% (V{sub OC} = 1.336 V, J{sub SC} = 4.65 mA/cm{sup 2}, FF = 41.98%) due to the eliminated interfacial series resistance.

Two low band gap copolymers (PQTDPP and PQTVTDPP) having quaterthiophene (QT) or bithiophene-vinylene-bithiophene (QTVT) as donor unit and diketopyrrolopyrrole (DPP) as acceptor unit have been synthesized via Stille cross-coupling polymerization. The polymers showed high thermal stability and broad light absorption with optical band gaps around 1.3 eV. Cyclic voltammetry measurements revealed that the HOMO and LUMO energy levels of QT and DPP copolymer (PQTDPP) were found to be −5.19 and −3.64 eV, respectively and those of PQTVTDPP −5.05 and −3.66 eV, respectively. X-ray diffraction patterns showed highly crystalline phase in the PQTDPP film and nearly amorphous in the PQTVTDPP film. This dramatic difference in crystallinity was attributed to the structural isomerization around vinyl groups in the PQTVTDPP polymer. Field-effect transistor measurement revealed that the PQTDPP showed high hole mobility of 0.06 cm 2 /Vs and on/off ratio of 10 6 while the PQTVTDPP showed hole mobility of 3.57×10 −4 cm 2 /Vs and on/off ratio of 10 5 , which is consistent with X-ray diffraction results. Photovoltaic devices were also fabricated using polymer:PCBM blends in the structure of ITO/PEDOT:PSS/blend/Al. The PQTDPP devices exhibited an open circuit voltage ( V oc ) of 0.58 V, a short circuit current ( J sc ) of 7.16 mA/cm 2 , a fill factor ( FF ) of 0.55 and a power conversion efficiency ( PCE ) of 2.28%, and the PQTVTDPP devices exhibited an V oc of 0.50 V, a J sc of 7.60 mA/cm 2 , a FF of 0.51 and a PCE of 1.97% under AM 1.5 illumination.

Thin-film solar cells based on hydrogenated amorphous silicon (a-Si:H) and conjugated polymers have been studied extensively. However, organic–inorganic hybrid tandem solar cells incorporating the two materials as subcells are yet to be extensively studied. Here, a computational study on the optimal design of organic–inorganic hybrid tandem solar cells to achieve the maximum possible efficiency is presented. The optical simulations predict the optimal design of an organic–inorganic hybrid tandem solar cell, desirable for a wide range of spectral response and high efficiency. The optimum combination of thicknesses of a-Si:H and organic photovoltaic (OPV) subcells to achieve the highest possible efficiency in terms of short circuit current (J sc) is determined. Thicknesses of 400 and 140 nm for a-Si:H and OPV subcells, respectively, are suggested for the optimised tandem solar cell to achieve current matching and a maximum power conversion efficiency of 11.57%.

It has long been believed as a law that electrons and mobile ions migrate independently in a mixed ionic electronic conductor compound. We have experimentally found that it is only an exception: the interference effect between electrons and ions upon their transfer is by no means negligible depending on the thermodynamic state of the system. We have also experimentally verified, with the highest ever precision, the Onsager reciprocity in the phenomenon of mixed conduction in solid state.

Flexible organic film speaker (FOFS) was fabricated with ion-assisted-reaction (IAR) treated poly(vinylidene fluoide) (PVDF) as active layer and poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS), indium tin oxide (ITO), or copper (Cu) as electrode. The PEDOT/PSS materials were screen printed on the PVDF surface. The dc conductivity ( σ dc ) of pristine PEDOT/PSS increases from 0.8 to ∼80 S/cm by adding various organic solvents. The sound pressure level (SPL) of PVDF-based FOFS with a highly conducting PEDOT/PSS (dimethyl sulfoxide, DMSO) electrode is 27 dB higher than that with a low conducting PEDOT/PSS (H 2 O) at 1 kHz. The highly conducting PEDOT/PSS (DMSO) as electrode is more suitable to PVDF-based FOFS compared to Cu or ITO because of the stable and more flat SPL, the flexibility, easy patterning, and coating process.

We have designed and manufactured a flanged coaxial line as a sample holder for measuring the electromagnetic interference (EMI) shielding efficiency (SE) of planar materials in broadband frequency ranges up to 18 GHz. Connecting the samples holder to a vector network analyzer (50 MHz⩽M⩽13.5 GHz), we measured the S (scattering)-parameters and the EMI SE of copper (Cu) as a highly conducting material and emeraldine salt form of polyaniline (PAN–ES) as an intermediately conducting one. The measured EMI SEs of the materials from 50 MHz to 13.5 GHz were compared with those obtained from the conventional ASTM D4935-99 method and theoretical simulation using dc conductivity. We observed that the EMI SEs measured by using both experimental techniques agree with each other in the common frequency range (50 MHz∼1.5 GHz). The EMI shielding characteristics of samples such as the contribution of absorption and reflection to total EMI SE were analyzed through the measured S parameters.

The DC conductivity ( σ DC ) of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(4-styrenesulfonate) (PSS) with various organic solvents was measured. The solvents used were dimethyl sulfoxide (DMSO), N , N -dimethyl formamide (DMF), tetrahydrofuran (THF), and H 2 O (as pristine solvent). Room temperature DC conductivity [ σ DC (RT)] of a free standing film of PEDOT/PSS with H 2 O was measured to be ∼0.8 S/cm. Through a change of solvents used, σ DC (RT) of the samples increases from ∼0.8 to ∼80 S/cm. The temperature dependence of DC conductivity [ σ DC ( T )] of PEDOT/PSS with H 2 O followed a quasi one-dimensional variable range hopping model, while that of PEDOT/PSS prepared from DMSO, DMF, and THF followed a power law ( σ DC ∝ T β ). From X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) experiments, the doping concentration of the systems with different solvents was approximately the same. We analyzed that the screening effect of the solvent plays an important role for the variation of σ DC of the PEDOT/PSS systems.

Electromagnetic interference (EMI) shielding materials of complex type of conductive polypyrrole (PPy) as an intrinsically conducting polymer and silver-palladium (AgPd) metal compound coated on woven or non-woven fabrics are synthesized. From dc conductivity and SEM photographs of PPy/fabric complexes, we discuss charge transport mechanism and the homogeneity of coating on the fabrics. The EMI shielding efficiency of PPy/fabric and AgPd/fabric complexes is in the range of 8 ∼ 80 dB depending on the conductivity and the additional Ag vacuum evaporation. The highest EMI shielding efficiency of PPy/fabric complexes vacuum-evaporated by Ag is ∼80 dB, indicating potential materials for military uses. We propose that PPy/fabrics are excellent RF and microwave absorber because of the relatively high absorbance and low reflectance of the materials. Copyright © 2002 John Wiley & Sons, Ltd.

Enhanced optical absorption of Poly(3-hexylthiophene) films deposited on the gold nanoparticle arrays was investigated. Highly dense arrays of gold nanoparticles were produced using the amphiphilic poly(styrene-block-4-vinylpyridine) diblock copolymer. The local electric field enhancement due to the localized surface plasmon resonance excitation of novel metal nanoparticles can increase the absorption of light from nearby photoactive materials. This result can be applicable to improve the solar harvesting in organic photovoltaics.

We have prepared transparent dielectric thick films for the plasma display panel (PDP) by adding Nd2O3 into transparent dielectric materials and investigated their optical properties. The experimental results revealed that, owing to absorptions originating in the intratransition within the 4f shell of the Nd3+ ion, the neodymium-containing transparent dielectrics act not only as dielectrics, but also as a band rejection color filter. As a result, introduction of the neodymium-containing transparent dielectrics to PDP device yields a wider color gamut and higher color purity.

In order to improve the primary color purity of the plasma display panel (PDP), inorganic (SiO2)1−x(Nd2O3)x alloy films have been fabricated by the rf-magnetron sputtering method, and their optical properties have been investigated as functions of Nd2O3 contents in films and thickness of films. The study has revealed that absorption in (SiO2)1−x(Nd2O3)x films is due to intratransition within the 4f shell of the Nd3+ ion, and that it becomes larger with increasing Nd3+ ion concentrations in films and film thickness. In the PDP devices with our band rejection color filters, luminances from neon gas discharge itself and sidebands of phosphors are sufficiently reduced, resulting in wider color gamut and higher color purity.

Electrical conductivity and oxygen nonstoichiometry (delta) have been measured, respectively, by a dc 4-probe technique and coulometric titrometry on the system of polycrystalline Ti0.99Ga0.01O1.995-delta against oxygen activity in the range of -20log aO2or = 0 at different temperatures in the range of 1073or =T/Kor = 1373. It is found that isothermal conductivity varies as sigma alpha aO2m with m approximately -1/4, -1/5, -1/4, +1/4, in order of increasing aO2, finally exhibiting an n-type (m = -1/4) to p-type (m = +1/4) transition crossing the stoichiometric composition (delta = 0), in perfect agreement with the oxygen nonstoichiometry variation. The electrical conductivity and oxygen nonstoichiometry isotherms are combined to evaluate the ionic partial conductivity and transference number, the intrinsic electronic excitation equilibrium constant, and eventually both mobilities of electrons and holes without employing any assumption at all. The partial molar enthalpy and entropy of the component oxygen are also evaluated as functions of nonstoichiometry.

Low-cost and printable chalcopyrite thin-film solar cells were fabricated by a precursor solution-based coating method with a multi-step heat-treatment process (oxidation, sulfurization, and selenization). The high-band-gap (1.57 eV) Cu(InxGa1−x)S2 (CIGS) solar cell showed a high open-circuit voltage of 787 mV, whereas the low-band-gap (1.12 eV) Cu(InxGa1−x)(S1−ySey)2 (CIGSSe) cell exhibited a high short-circuit current density of 32.6 mA cm−2. The energy conversion efficiencies were 8.28% for CIGS and 8.81% for CIGSSe under standard irradiation conditions. Despite similar efficiencies, the two samples showed notable differences in grain size, surface morphology, and interfacial properties. Low-temperature transport and admittance characteristics of the samples clearly revealed how their structural differences influenced their photovoltaic and electrical properties. Such analyses provide insight into the enhanced solar cell performance of the solution-processed chalcopyrite thin films.

An interparticle binding agent, or nanoglue, was synthesized by a sol-gel process, which facilitated the preparation of well-interconnected TiO2 electrodes at low-temperatures for plastic dye-sensitized solar cells. The viscosity of the nanoglue-based pastes was seven times higher than that obtained in pastes without any nanoglue. The increased viscosity was sufficiently high enough for coating thick films to fabricate TiO2 electrodes. The structural and photovoltaic properties of the films were extensively investigated by varying the amounts of nanoglue. A reduced pore size and greatly enhanced surface area were observed in the nanoglue-based films. Improved interparticle connectivity, resulting in faster electron transport, was confirmed by photocurrent transient spectroscopy and electrochemical impedance measurements of the nanoglue-based films. The electron diffusion length and charge collection efficiency were also enhanced in these nanoglue-based films. A maximum conversion efficiency of 5.43% was achieved in films containing 20 wt% nanoglue fabricated on a plastic substrate under one-sun illumination, even without any additional treatment.

We demonstrate series-connected hybrid tandem multijunction photovoltaics by combining hydrogenated amorphous silicon (a-Si:H) and polymer-based organic photovoltaics (OPVs). To utilize the wide solar spectrum with cost-effective processes, we employed a solution-processed low band gap OPV subcell onto the a-Si:H subcell. The interfacial contact between the subcells strongly affects the photovoltaic performance of the tandem cells. By using MoO3 as an efficient hole transporting intermediate layer instead of the conventional conducting polymer, we obtained power conversion efficiency of 1.84% and open-circuit voltage (VOC) of 1.50 V which corresponds closely to the sum of VOCs of the subcells.

An interparticle-binding agent, or “nanoglue,” was prepared for the fabrication of well-interconnected TiO2 photoelectrodes in dye-sensitized solar cells (DSSCs) sintered at low temperature. This nanoglue consisted of pure anatase particles approximately 5 nm in diameter dispersed in alcoholic solvent. When mixed with TiO2 particles 21 nm in diameter, the nanoglue induced interparticle chemical bridging via the condensation of hydroxyl groups on surfaces of TiO2 particles. The efficiency of nanoglue-based DSSCs was improved by approximately 25% compared to non-nanoglue-based DSSCs. This improvement was mainly ascribed to enhanced interparticle connections due to the presence of the 5 nm TiO2 particles in nanoglue.

We have investigated effect of thin TiO2 layers deposited on an indium tin oxide (ITO)/fluorine-doped tin oxide (FTO) double-layered transparent conductive oxide on the performance of dye-sensitized solar cell. FTO is deposited on an ITO-coated glass, followed by TiO2 deposition using a radio frequency magnetron sputtering technique. The thicknesses of the sputtered-TiO2 layers are varied from 10 nm to 20 nm, while the ITO and FTO are fixed to be 150 nm and 70 nm, respectively. Atomic force microscopy (AFM) shows that the surface roughness is similar but the surface morphology is altered by thin TiO2 layer deposition. The sheet resistance of the ITO/FTO conductive glass is hardly changed by thin TiO2 layer deposition. Photovoltaic performance is significantly enhanced after introduction of thin TiO2 underlayer. The 15 nm thick TiO2 underlayer leads to the increases of photocurrent density from 9 mA cm−2 to 10.3 mA cm−2 and fill factor from 0.715 to 0.747, as a result, the overall conversion efficiency is improved from 5.28% to 6.37%, corresponding to 20.6% increase. Photovoltage, however, remains almost unchanged. Photocurrent is improved over the entire wavelength. The increased transmittance at wavelength ranging from 300 to 600 nm contributes in part to increase in photocurrent. Improvement of charge collection efficiency from ∼90% to ∼97% is also attributed to the increased photocurrent, where the increased transport rate is responsible for the improved charge collection, indicating that the thin TiO2 underlayer has influence on opto-electronic property in the dye-adsorbed bulk TiO2 film.

A crystallographic cage structure endows mayenite (Ca(12)Al(14)O(33) or 12CaO.7Al(2)O(3); C(12)A(7)) with remarkable properties, making it either an oxygen solid electrolyte or an inorganic electride upon reduction. In order to better understand the transport properties of C(12)A(7), we measured the equilibrium total conductivity as well as the electronic partial conductivity of single crystal mayenite as functions of activity of oxygen or water vapor at different temperatures in the range 1073or =T/Kor = 1273. A point defect model based on the assumption that the framework [Ca(12)Al(14)O(32)](2+) acts as a pseudo-donor describes well the isothermal conductivity vs. oxygen activity, enabling us to deconvolute the ionic and electronic partial conductivities. The ionic transference number evaluated therefrom clearly demonstrates how C(12)A(7) is converted from a solid electrolyte to an electride depending on the oxygen content. In addition, besides the well known degradation of ionic conductivity by water uptake, a short-term increase of conductivity upon abrupt hydration was recognized and interpreted as due to the transient increase in the concentration of oxygen interstitial along with proton in the initial stage of hydration. For the fully hydrated C(12)A(7), the conductivity relaxation curves upon switching of oxygen activity in a fixed water vapor pressure appear non-monotonic showing the extrema only in the plateau conductivity regime. A defect structure based hypothesis is proposed to explain the 2-fold re-equilibration kinetics.