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The Eu3+ ion is not only an efficient red-emitting activator, but also a well-known spectral probe. In this work, a series of Cs2Mg2Mo3O12:2xEu3+ (x = 0–0.1) phosphors are successfully synthesized using the solid-state reaction. Rietveld refinements confirmed the cubic structure of Eu3+-doped Cs2Mg2Mo3O12 with the P213 space group (no: 198), in which the activators substituted for the Cs+ lattice positions. The phosphor exhibited a sharp luminescence line at 613 nm (5D0 to 7F2 of Eu3+) with a half-bandwidth of approximately 1 nm. The remarkable CIE chromaticity coordinates (x = 0.66, y = 0.33) are close to the ideal red chromaticity specified by the NTSC. Unfortunately, the optimal luminescence of Cs2Mg2Mo3O12:2xEu3+ was quenched at a low concentration of 5.0 at% (x = 0.05). The quenching mechanism was analyzed through the Eu3+-site occupations and the corresponding dynamic spectra were obtained using the laser site-selective spectroscopy technique. In the samples with low doping levels of Cs2Mg2Mo3O12:2xEu3+ (x ≦ 0.05), only one Eu3+ center was regularly arranged on Cs(2) sites. Beyond this level of doping in Cs2Mg2Mo3O12:2xEu3+ (x = 0.07, 0.1), Eu3+ began to occupy Cs(1) sites in the lattices in addition to Cs(2). The site-selective luminescence and decay characteristics confirmed that the two Eu3+ centers occupying Cs(1) and Cs(2) sites had sufficient energy transfer (ET) between them. In this case, the excitation energy was easily lost during the excitation process. This study demonstrates that the substitution position of the Eu3+ activator in the lattice can greatly affect the quenching performance of red emission. [ABSTRACT FROM AUTHOR]

Oxide semiconductors with mixed-valence states generally exhibit excellent optoelectronic and photochemical properties due to facile charge transfer in redox reactions. In this work, we investigate the effects of mixed alkali on the optical absorption, luminescence spectra and photocatalytic abilities of (Na1−xKx)Sb3O7 nanoparticles. All the samples are fabricated using a simple one-step hydrothermal method. The structural studies show that the largest substitution of K+ ions in (Na1−xKx)Sb3O7 is at x = 0.3. In hydrothermal synthesis, the mixed arrangement of K+ and Na+ in (Na1−xKx)Sb3O7 has an influence on the crystal shape of particles. NaSb3O7 develops into a regular cube shape. With the increase of K+ ions in (Na1−xKx)Sb3O7, the edges and corners of the cube are further ground off, resulting in irregularly spherical particles. This mixed-alkali antimonite belongs to a p-type indirect allowed transition semiconductor, and the optical band gap is 2.71 eV (x = 0.3). The intrinsic luminescence of NaSb3O7 is detected at 540 nm, which is nearly quenched in Na0.7K0.3Sb3O7. It is demonstrated that the substitution of K+ in NaSb3O7 significantly increases the photodegradation of RhB solutions. There are two types of Sb cations, i.e., Sb5+ and Sb3+ mixed in the structure. The improved photocatalysis is attributed to the charge mediators between Sb5+/Sb3+ couples. The experiment shows that co-doping cations in antimonite oxides may be one of the strategies to improve photochemical properties. [ABSTRACT FROM AUTHOR]

We developed an ionic energy harvester based on polymer hydrogels, which was designed to harvest low-frequency mechanical vibrations by taking advantage of the slow diffusion of ions. Our ionic devices are composed of three-layered polymer hydrogels with different stiffnesses and ion selectivities. Under mechanical compression, the inhomogeneous volume changes of the component hydrogels induced massive and directional ion transport, while the ion selectivities of the hydrogels allowed charge separation of the transporting ions into cations and anions through the stacked hydrogels. Consequently, an electric potential difference was built within the layered hydrogels, allowing the conversion of mechanical energy into electricity. This mechanical-to-electrical energy conversion was engineered under a number of experimental conditions. Under the optimized conditions, our hydrogel devices produced an open-circuit voltage of 12 mV and a short-circuit current density of 72.5 μA cm−2 at 0.008 Hz. We further demonstrated the synthesis of inorganic nanoparticles and energy generation from human walking by implanting the prepared ionic devices into a metal precursor solution and shoes, respectively. Collectively, this study provides a blueprint for the future development of hydrogel-based ionic energy harvesters as soft and flexible power sources for many self-powered systems. [ABSTRACT FROM AUTHOR]

In polymer solar cells (PSCs), electrolytes as the cathode interlayer are responsible for generating an interface dipole, which reduces the charge collection barrier at the cathode interface. In this study, small-molecule electrolytes were designed and synthesized as the cathode interlayer in inverted PSCs to overcome high processing costs caused by complicated synthesis procedures. Moreover, the proposed design strategy allows changing the ion size and number of ionic functionalities to tune the magnitude of the interface dipole. The structure of ((benzene-1,2,4,5-tetrayltetrakis(methylene))tetrakis(triphenylphosphonium) bromide) (4PBr) comprises a phenyl core with four benzyl triphenylphosphonium salts and (N,N′-(1,2-phenylenebis(methylene))bis(N,N-diethylethanaminium) bromide) (2EBr) has two benzyl trialkyl ammonium salts. The device based on 4PBr exhibited a power conversion efficiency of 10.63% (Jsc = 20.2 mA cm−2, Voc = 0.79 V, and FF = 66.6%), which is superior to that based on 2EBr (PCE = 9.56%, Jsc = 19.7 mA cm−2, Voc = 0.80 V, and FF = 61.1%). Thus, we demonstrated the possibility of maximizing performances without complicated synthesis procedures. [ABSTRACT FROM AUTHOR]

To investigate the effect of the electron-withdrawing cyano (CN) substituent on the photovoltaic properties of polymers, three quinoxaline (Qx)-based polymers are designed and synthesized. The reference polymer (PTB-FQx) was prepared via polymerization between benzodithiophene (BDT) and mono-fluorinated Qx monomers, and the fluorine atom of PTB-FQx was replaced by a CN substituent to create the target polymer PTB-CNQx. In addition, another target polymer PTBF-CNQx was prepared by incorporating additional fluorine atoms on the two thiophene side chains of the BDT unit in PTB-CNQx. The photovoltaic performances of all polymers were comprehensively examined by fabricating both fullerene and nonfullerene polymer solar cells (PSCs). Owing to the affirmative contributions of the CN substituent, PSCs based on CN-substituted PTB-CNQx exhibit higher power conversion efficiencies (PCEs) than the corresponding devices with the fluorinated PTB-FQx reference. Moreover, further increases in the PCE of up to 9.2 and 14.0% were achieved for the devices based on PTBF-CNQx with fullerene and nonfullerene acceptors, respectively. To the best of our knowledge, this study can offer not only the first direct comparison of the photovoltaic properties of the F and CN substituents of conjugated polymers but also the highest PCEs among the reported CN-substituted polymers in both categories of fullerene and nonfullerene PSCs. [ABSTRACT FROM AUTHOR]

We fabricated and tested inverted polymer solar cells (PSCs) that use a blend of PTB7-Th and PC71BM as the active layer and poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dihexylfluorene)] (PFN) with different amounts and types of acid derivatives as the cathode buffer layer to systematically study the effect of amounts and types of acid additives such as acetic acid (AA), 4-trifluoromethyl benzoic acid (CF3BA), trifluoroacetic acid (CF3AA), and 4-toluene sulfonic acid (TsOH) on the device performances. Consequently, a significant improvement was obtained for the device based on ZnO/PFN with 1.0 equivalent (eq.) of acid derivatives. The PCE of the device with 1.0 equivalent of AA, CF3BA, CF3AA, and TsOH was 9.9, 10.3, 10.3, and 10.6% respectively, whereas the power conversion efficiency (PCE) of the device with pristine ZnO was 8.7%. The performances of the devices followed the trend of the acid dissociation constant of acid derivatives. In addition, we discovered that the most effective acid derivative is TsOH. Furthermore, we observed that the devices based on PFN with acid derivatives exhibited reduced trap-assisted recombination and interfacial bimolecular recombination. Furthermore, reduced trap-assisted recombination of the devices agreed well with the trend of the PCEs of PSCs and followed the trend of the acid dissociation constant of acid derivatives. [ABSTRACT FROM AUTHOR]

The performance of polymer–fullerene bulk heterojunction (BHJ) solar cells is highly affected by the morphology of the blend film. Though the structure of the BHJ morphology is well-understood, the relationship between relevant material interactions and BHJ morphological evolutions is poorly understood and seldom explored. In this report, we discuss the impact of polymer molecular weight (MW) on thermodynamic and kinetic phenomena which have a drastic influence on the nanoscale BHJ morphology. The blend film comprises a highly aggregating low bandgap diketopyrrolopyrrole-based polymer PDPP3T and the fullerene electron acceptor molecule PC71BM, cast from a 1,2-dichlorobenzene (DCB) solution with and without the additive 1,8-diiodooctane (DIO). The pair-wise interactions among the components were evaluated by Flory–Huggins interaction parameters (χ). The BHJ blend of PDPP3T and PC71BM exhibited liquid–liquid (L–L) phase separation as a result of strong polymer–fullerene interactions (large χPDPP3T–fullerene) in DCB solution. In contrast, addition of 3% DIO into the DCB solution is found to stimulate polymer aggregation which gives rise to liquid–solid (L–S) phase separation. Large χPDPP3T–fullerene and χPDPP3T–solvent were observed as a result of increasing polymer MW, and these changes promote strong L–L phase separation and polymer aggregation in the blend solution, respectively. The latter interactions have led to low molecular mobility, with an end result of reduced crystallinity and smaller domain size of the BHJ films. The observed dramatic MW-dependent morphological changes were also manifested in solar cell outputs as well as charge carrier dynamics calculated by transient absorption measurements. [ABSTRACT FROM AUTHOR]

Non-fullerene acceptors (NFAs) are becoming a serious contender to fullerene-based electron acceptors in organic photovoltaics, due to their structural versatility and easily tunable optical and electronic properties. However, NFA-based solar cells often have a decreased short-circuit current (Jsc) and fill factor (FF) compared to their fullerene-based counterparts. Here, we investigate the fundamental causes of this decrease in the performance of solar cells using a non-fullerene acceptor (SF-PDI2) paired with two polymer donors, FTAZ and PyCNTAZ, compared with their fullerene-based counterparts. Through a number of experimental techniques and morphological studies, we show that the SF-PDI2-based solar cells suffer from insufficient charge generation, transport, and collection when compared with the PCBM-based solar cells. The SF-PDI2-based solar cells show increased bimolecular recombination, which, together with other recombination loss mechanisms in these cells, causes a significant decrease in their Jsc and FF. Notably, the less pure domains, low electron mobility (on the order of 10−5 cm2 V−1 s−1), and imbalanced mobility (in regard to the hole mobility) further explain the low FF. On the other hand, the higher open-circuit voltage (Voc) in the SF-PDI2 devices is mainly due to the increase in the CT state energy. It is worth mentioning that the PyCNTAZ-based devices show an ultralow charge separation energy (ΔECS), close to 0 eV. Our results demonstrate that further increasing the mobility (both of electrons and holes) in these NFA-based solar cells would be a viable approach to further enhance the efficiency of these new types of solar cells, ideally, without losing the high Voc of such cells. [ABSTRACT FROM AUTHOR]

We demonstrate the dual advantages of graded photoabsorbers in mesoporous metal oxide-based hetero interfacial photoanodes in improving photogenerated charge carrier (e−/h+) separation for the solar light-driven water-oxidation process. The pre-deposition of sol–gel-derived, tungsten-doped bismuth vanadate (W:BiVO4) onto a primary BiVO4 water oxidation layer forms graded interfaces, which facilitate charge transfer from the primary photoabsorber to the charge transport layer, thereby superseding the thickness-controlled charge recombination at the BiVO4 water oxidation catalyst. As a result, the WO3/BiVO4 hetero photoanode containing the photoactive W:BiVO4 interfacial layer showed 130% higher photocurrent than that of the interfacial layer-free hetero photoelectrode owing to the enhanced charge separation led water oxidation process. [ABSTRACT FROM AUTHOR]

Sn is a promising anode material for sodium ion batteries due to its high capacity. However, the fast capacity fading caused by large volume changes limits the employment of Sn anodes. Graphene has been considered as a host for Sn anode materials to improve the cycle performance. However, graphene scaffold preparation with large free spaces is challenging due to the need for a sacrificial template and etching process. Here, we prepared a porous scaffold composed of both reduced graphene oxide and graphene via a camera flash reduction as the host for Sn. The camera flash induces the reduction of the graphene oxide and pores generated by the c-axis popping of the graphene. The mechanical strength of the scaffold is also achieved by adjusting the concentration of graphene which does not react with the flash light. The porosity and mechanical properties of the reduced graphene oxide–graphene scaffold could be controlled by flash irradiation conditions and the mixing ratio between the graphene oxide and graphene. The porous scaffold enables a uniform Sn loading and an improvement in the sodium ion battery performance due to a sufficient free space for accommodating the Sn volume change and mechanical stability. [ABSTRACT FROM AUTHOR]

We first demonstrate a facile and effective strategy to directly deposit a Nafion nanoweb onto a sulfur cathode to address the challenges underlying in Li–S batteries. The Nafion nanoweb not only blocks the diffusion of polysulfides by electrostatic repulsion but also allows fast Li-ion exchange with the sulfur cathode through the selective protection layer. The Nafion nanoweb-sulfur cathode retained an excellent cycle performance over 200 cycles and delivered an improved rate capability, as compared to a sulfur cathode and a Nafion layer-sulfur cathode. [ABSTRACT FROM AUTHOR]

Here a series of isoindigo (ID) and quaterthiophene (T4)-based donor–acceptor copolymers are synthesized and compared. The polymer with fluorination on the donor unit exhibits the strongest extent of temperature-dependent aggregation, which leads to a higher hole mobility of the polymer and PSCs with efficiencies up to 7.0% without using any processing additives. Our results provide important insights into how fluorination affects the aggregation properties and performance of isoindigo-based polymers. [ABSTRACT FROM AUTHOR]

We report a stackable all-solid-state supercapacitor based on three dimensional PPy–NiO/RGO–CNT electrodes. The electrodes were prepared by growing NiO nanowalls (NWs) on both sides of a freestanding RGO–CNT film with the hydrothermal method, followed by coating with conductive polypyrrole. The double-sided architecture of the NiO NWs on a carbon-based current collector suggests that the novel approach addresses the issue of low areal capacitance in supercapacitors. Furthermore, conductive polypyrrole renders fast electron transport through the two-dimensional structure of NiO NWs. With our 3D-designed electrodes, we successfully fabricated a stackable all-solid-state supercapacitor and thus achieved a high areal capacitance of 1948 mF cm−2. [ABSTRACT FROM AUTHOR]

Hydroxylated multi-walled carbon nanotubes were introduced into sulfur cathodes to utilize the hydrophilic attraction between the OH group and polysulfides as well as to increase the utilization of sulfur. This approach shows a promising strategy for diminishing the polysulfides shuttling behavior and improving the electrochemical performance of lithium–sulfur batteries. [ABSTRACT FROM AUTHOR]

A non-conjugated polymer with a polar hydroxyl group as a side group, poly(vinyl alcohol) (PVA), is applied to polymer solar cells (PSCs) and polymer light-emitting diodes (PLEDs) as a buffer layer at the active layer/cathode interface. The best power conversion efficiency (PCE) of PSCs with the PVA film as a cathode buffer layer is 3.27%, which is a 27% increase compared to that of PSCs without the PVA film (2.58%). The PCE improvement is due to enhancement of the short circuit current, the fill factor, and the open circuit voltage, simultaneously. Also, the performances of polymer light-emitting diodes with the PVA film as a cathode buffer layer are better than those of the devices without PVA. Improvement of the performances of the devices is due to the fact that the PVA film reduces a Schottky barrier by the formation of favorable interface dipoles and improves the interface properties. [ABSTRACT FROM AUTHOR]

Here, we report the preparation of well-controlled nanoscale morphologies in photoactive thin films. The fabrication of bulk heterojunction structures in blend films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) employed two steps to achieve first the in situformation of self-organized P3HT nanowires using a marginal solvent, and second, phase separation viamild thermal annealing. Morphological changes in the active layers that had been spin-cast from a marginal solvent, with varying annealing temperatures, were systematically studied and compared to the morphologies of films spin-cast from a good solvent. The interpenetrating nanowire structure yielded power conversion efficiencies as high as 4.07% due to the enhanced charge transport. Hole and electron mobilities increased substantially to 1.6 × 10−3cm2V−1s−1and 1.4 × 10−3cm2V−1s−1, respectively, due to the two step process of P3HT crystallization by nanowire formation and subsequent phase separation. Photovoltaic performances improved with increasing film thickness up to 300 nm as a result of the interpenetrating donor/acceptor network structure. [ABSTRACT FROM AUTHOR]

Here, we report the preparation of well-controlled nanoscale morphologies in photoactive thin films. The fabrication of bulk heterojunction structures in blend films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) employed two steps to achieve first the in situformation of self-organized P3HT nanowires using a marginal solvent, and second, phase separation viamild thermal annealing. Morphological changes in the active layers that had been spin-cast from a marginal solvent, with varying annealing temperatures, were systematically studied and compared to the morphologies of films spin-cast from a good solvent. The interpenetrating nanowire structure yielded power conversion efficiencies as high as 4.07% due to the enhanced charge transport. Hole and electron mobilities increased substantially to 1.6 × 10−3cm2V−1s−1and 1.4 × 10−3cm2V−1s−1, respectively, due to the two step process of P3HT crystallization by nanowire formation and subsequent phase separation. Photovoltaic performances improved with increasing film thickness up to 300 nm as a result of the interpenetrating donor/acceptor network structure. [ABSTRACT FROM AUTHOR]

A new π-conjugated polymer, poly(2,5-dioctyloxyphenylene vinylene-alt-3,3-dioctylquater thiophene) (PPVQT-C8), consisting of alternating p-divinylene phenylene and 3,3-dialkylquater thiophene units, was synthesized for use in organic solar cell devices. The crystallinity of poly(quaterthiophenes) (PQTs) was reduced by introducing p-divinylene phenylene units between pairs of quaterthiophene units. A well-mixed nanoscale morphology of PPVQT-C8:PCBM photoactive layer resulted from this modification, which increased the power conversion efficiency relative to devices based on highly crystalline PQTs. Bulk heterojunction solar cells based on PPVQT-C8:PC60BM blends with a 1 : 3 ratio presented the best photovoltaic performances, with a short-circuit current density (Jsc) of 6.7 mA cm−2, an open-circuit voltage (Voc) of 0.67 V, a fill factor (FF) of 0.62 and a power conversion efficiency (PCE) of 2.8% under illumination of AM 1.5 with light intensity of 100 mW cm−2. The charge carrier mobility and morphology studies indicated that an optimized interpenetration network composed of PPVQT-C8: PCBM could be achieved in a blend ratio of 1 : 3. [ABSTRACT FROM AUTHOR]

Oxide semiconductors with mixed-valence states generally exhibit excellent optoelectronic and photochemical properties due to facile charge transfer in redox reactions. In this work, we investigate the effects of mixed alkali on the optical absorption, luminescence spectra and photocatalytic abilities of (Na1−xKx)Sb3O7 nanoparticles. All the samples are fabricated using a simple one-step hydrothermal method. The structural studies show that the largest substitution of K+ ions in (Na1−xKx)Sb3O7 is at x = 0.3. In hydrothermal synthesis, the mixed arrangement of K+ and Na+ in (Na1−xKx)Sb3O7 has an influence on the crystal shape of particles. NaSb3O7 develops into a regular cube shape. With the increase of K+ ions in (Na1−xKx)Sb3O7, the edges and corners of the cube are further ground off, resulting in irregularly spherical particles. This mixed-alkali antimonite belongs to a p-type indirect allowed transition semiconductor, and the optical band gap is 2.71 eV (x = 0.3). The intrinsic luminescence of NaSb3O7 is detected at 540 nm, which is nearly quenched in Na0.7K0.3Sb3O7. It is demonstrated that the substitution of K+ in NaSb3O7 significantly increases the photodegradation of RhB solutions. There are two types of Sb cations, i.e., Sb5+ and Sb3+ mixed in the structure. The improved photocatalysis is attributed to the charge mediators between Sb5+/Sb3+ couples. The experiment shows that co-doping cations in antimonite oxides may be one of the strategies to improve photochemical properties. [ABSTRACT FROM AUTHOR]

Oxide semiconductors with mixed-valence states generally exhibit excellent optoelectronic and photochemical properties due to facile charge transfer in redox reactions. In this work, we investigate the effects of mixed alkali on the optical absorption, luminescence spectra and photocatalytic abilities of (Na 1- x K x )Sb 3 O 7 nanoparticles. All the samples are fabricated using a simple one-step hydrothermal method. The structural studies show that the largest substitution of K + ions in (Na 1- x K x )Sb 3 O 7 is at x = 0.3. In hydrothermal synthesis, the mixed arrangement of K + and Na + in (Na 1- x K x )Sb 3 O 7 has an influence on the crystal shape of particles. NaSb 3 O 7 develops into a regular cube shape. With the increase of K + ions in (Na 1- x K x )Sb 3 O 7 , the edges and corners of the cube are further ground off, resulting in irregularly spherical particles. This mixed-alkali antimonite belongs to a p-type indirect allowed transition semiconductor, and the optical band gap is 2.71 eV ( x = 0.3). The intrinsic luminescence of NaSb 3 O 7 is detected at 540 nm, which is nearly quenched in Na 0.7 K 0.3 Sb 3 O 7 . It is demonstrated that the substitution of K + in NaSb 3 O 7 significantly increases the photodegradation of RhB solutions. There are two types of Sb cations, i.e. , Sb 5+ and Sb 3+ mixed in the structure. The improved photocatalysis is attributed to the charge mediators between Sb 5+ /Sb 3+ couples. The experiment shows that co-doping cations in antimonite oxides may be one of the strategies to improve photochemical properties.

We demonstrate the dual advantages of graded photoabsorbers in mesoporous metal oxide-based hetero interfacial photoanodes in improving photogenerated charge carrier (e - /h + ) separation for the solar light-driven water-oxidation process. The pre-deposition of sol-gel-derived, tungsten-doped bismuth vanadate (W:BiVO 4 ) onto a primary BiVO 4 water oxidation layer forms graded interfaces, which facilitate charge transfer from the primary photoabsorber to the charge transport layer, thereby superseding the thickness-controlled charge recombination at the BiVO 4 water oxidation catalyst. As a result, the WO 3 /BiVO 4 hetero photoanode containing the photoactive W:BiVO 4 interfacial layer showed 130% higher photocurrent than that of the interfacial layer-free hetero photoelectrode owing to the enhanced charge separation led water oxidation process.