Additive Engineering by Bifunctional Guanidine Sulfamate for Highly Efficient and Stable Perovskites Solar Cells.

High efficiency and good stability are the challenges for perovskite solar cells (PSCs) toward commercialization. However, the intrinsic high defect density and internal nonradiative recombination of perovskite (PVK) limit its development. In this work, a facile additive strategy is devised by introducing bifunctional guanidine sulfamate (GuaSM; CH6 N3 + , Gua+ ; H2 N-SO3 - , SM- ) into PVK. The size of Gua+ ion is suitable with Pb(BrI)2 cavity relatively, so it can participate in the formation of low-dimensional PVK when mixed with Pb(BrI)2 . The O and N atoms of SM- can coordinate with Pb2+ . The synergistic effect of the anions and cations effectively reduces the trap density and the recombination in PVK, so that it can improve the efficiency and stability of PSCs. At an optimal concentration of GuaSM (2 mol%), the PSC presents a champion power conversion efficiency of 21.66% and a remarkably improved stability and hysteresis. The results provide a novel strategy for highly efficient and stable PSCs by bifunctional additive.

Counter electrodes in dye-sensitized solar cells.

Dye-sensitized solar cells (DSSCs) are regarded as prospective solar cells for the next generation of photovoltaic technologies and have become research hotspots in the PV field. The counter electrode, as a crucial component of DSSCs, collects electrons from the external circuit and catalyzes the redox reduction in the electrolyte, which has a significant influence on the photovoltaic performance, long-term stability and cost of the devices. Solar cells, dye-sensitized solar cells, as well as the structure, principle, preparation and characterization of counter electrodes are mentioned in the introduction section. The next six sections discuss the counter electrodes based on transparency and flexibility, metals and alloys, carbon materials, conductive polymers, transition metal compounds, and hybrids, respectively. The special features and performance, advantages and disadvantages, preparation, characterization, mechanisms, important events and development histories of various counter electrodes are presented. In the eighth section, the development of counter electrodes is summarized with an outlook. This article panoramically reviews the counter electrodes in DSSCs, which is of great significance for enhancing the development levels of DSSCs and other photoelectrochemical devices.

Carbon-reinforced Ni3S2/Ti3C2Tx MXene composite as an anode for superior-performance lithium-ion capacitors.

Lithium ion capacitors (LICs) are a new generation of energy storage devices that combine the super energy storage capability of lithium ion batteries with the satisfactory power density of supercapacitors. The development of high-performance LICs still faces great challenges due to the unbalanced reaction kinetics at the anode and cathode. Therefore, it is an inevitable need to enhance the electron/ion transfer capability of the anode materials. In this paper, to obtain a superior-rate and high-capacity Ni3S2-based anode, highly conductive Ti3C2Tx MXene sheets were introduced to sever as the carrier of Ni3S2 nanoparticles and simultaneously an amorphous carbon layer which coats onto the surface of Ni3S2 nanoparticles was in-situ generated by the carbonization of dopamine reactant. The as-synthesized Ni3S2/Ti3C2Tx/C composite exhibits a high specific surface area (112.6 m2/g) because of the addition of Ti3C2Tx that can reduce the aggregation of Ni3S2 nanoparticles and the in-situ generated amorphous carbon layer that can suppress the growth of Ni3S2 nanoparticles. The Ni3S2/Ti3C2Tx/C anode possesses a remarkable reversible discharge specific capacity (626.0 mAh/g under 0.2 A/g current density), which increases to 1150.8 mAh/g after 400-cycle charge/discharge measurement at the same measurement condition indicating eminent cyclability, along with superior rate capability. To construct a superior-performance LIC device, a sterculiae lychnophorae derived porous carbon (SLPC) cathode with an average discharge specific capacity of 73.4 mAh/g@0.1A/g was prepared. The Ni3S2/Ti3C2Tx/C//SLPC LIC device with optimal cathode/anode mass ratio has a satisfactory energy density ranging from 32.8 to 119.1 Wh kg-1 at the corresponding power density of 8799.4 to 157.5 W kg-1, together with a prominent capacity retention (95.5 %@1 A/g after 10,000 cycles).

Poly(3-hexylthiophene)/perovskite Heterointerface by Spinodal Decomposition Enabling Efficient and Stable Perovskite Solar Cells.

The best research-cell efficiency of perovskite solar cells (PSCs) is comparable with that of mature silicon solar cells (SSCs); However, the industrial development of PSCs lags far behind SSCs. PSC is a multiphase and multicomponent system, whose consequent interfacial energy loss and carrier loss seriously affect the performance and stability of devices. Here, by using spinodal decomposition, a spontaneous solid phase segregation process, in situ introduces a poly(3-hexylthiophene)/perovskite (P3HT/PVK) heterointerface with interpenetrating structure in PSCs. The P3HT/PVK heterointerface tunes the energy alignment, thereby reducing the energy loss at the interface; The P3HT/PVK interpenetrating structure bridges a transport channel, thus decreasing the carrier loss at the interface. The simultaneous mitigation of energy and carrier losses by P3HT/PVK heterointerface enables n-i-p geometry device a power conversion efficiency of 24.53% (certified 23.94%) and excellent stability. These findings demonstrate an ingenious strategy to optimize the performance of PSCs by heterointerface via Spinodal decomposition.

A reversible redox strategy for SWCNT-based supercapacitors using a high-performance electrolyte.

In order to achieve pesudocapacitive performance of single-wall carbon nanotube (SWCNT) electrodes, a high-efficient and reversible redox strategy utilizing a redox-mediated electrolyte for SWCNT-based supercapacitors is reported. In this novel redox-mediated electrolyte, the single-electrode specific capacitance of the supercapacitor is heightened four times, reaching C=162.66 F g(-1) at 1 A g(-1). The quick charge-discharge ability of the supercapacitor is also enhanced, and the relaxation time is as low as 0.58 s. Furthermore, the supercapacitor shows an excellent cycling performance of 96.51 % retention after 4000 cycles. The remarkable results presented here illustrate that the redox strategy is a facile and straightforward approach to improve the performances of SWCNT electrodes.

Amorphous Co-Mo-S nanospheres fabricated via room-temperature vulcanization for asymmetric supercapacitors.

Ternary metal sulfides employed in supercapacitors exhibit better electrochemical performances than their counterpart oxides due to their superior conductivity. However, the insertion/extraction of electrolyte ions can lead to a significant volume change in electrode materials, which can result in poor cycling stability. Herein, novel amorphous Co-Mo-S nanospheres were fabricated through a facile room-temperature vulcanization method. It involves the conversion of crystalline CoMoO4 by reacting it with Na2S at room temperature. In addition to the conversion of the crystalline state into an amorphous structure with more grain boundaries, which is beneficial for the transport of electron/ion and can accommodate the volume change generated by the insertion/extraction of electrolyte ions, the production of more pores led to an increased specific surface area. The electrochemical results indicate that the as-prepared amorphous Co-Mo-S nanospheres had a specific capacitance of up to 2049.7F/g@1 A/g together with good rate capability. The amorphous Co-Mo-S nanospheres can be used as the cathode of supercapacitors and assembled with an activated carbon anode into an asymmetric supercapacitor possessing a satisfactory energy density of 47.6 Wh kg-1@1012.9 W kg-1. One of the prominent features exhibited by this asymmetric device is its remarkable cyclic stability, with a capacitance retention of 107% after 10,000 cycles.

Poly[diaqua-tris(µ(4)-isophthalato)dilanthanum(III)].

In the title coordination polymer, [La(2)(C(8)H(4)O(4))(3)(H(2)O)(2)](n), there are two independent La(III) atoms which are coordinated differently in slightly distorted penta-gonal-bipyramidal and slightly disorted bicapped trigonal-prismatic environments. The La(III) ions are bridged by µ(4)-isophthalate ligands, forming two-dimensional layers. In the crystal structure, these layers are connected by inter-molecular O-H⋯O hydrogen bonds into a three-dimensional network.

Poly[[diaqua-bis-(µ(3)-isonicotinato-κN:O:O')bis-(µ(2)-isonicotinato-κN:O)gadolinium(III)disiliver(I)] nitrate monohydrate].

In the title compound, {[Ag(2)Gd(C(6)H(4)NO(2))(4)(H(2)O)(2)]NO(3)·H(2)O}(n), the Gd(III) ion is coordinated by eight O atoms from six isonicotinate ligands and two water mol-ecules in a distorted square anti-prismatic geometry. Two Ag(I) ions are each bonded to two N atoms from two isonicotinate ligands in a linear or bow-like fashion [N-Ag-N angles = 178.6 (2) and 147.1 (2)°]. These metal ions are connected by the isonicotin-ate ligands into a layer parallel to (010). O-H⋯O hydrogen bonds donated by the coordinated and uncoordinated water mol-ecules and intra-layer π-π stacking inter-actions between the pyridine rings [centroid-centroid distances = 3.551 (4) and 3.555 (4) Å] are observed. The layers inter-act with each other by inter-layer Ag⋯O(aqua) contacts [2.731 (4) Å] and π-π stacking inter-actions between the pyridine rings [centroid-centroid distances = 3.466 (3) and 3.516 (3) Å], resulting in the formation of a three-dimensional supra-molecular structure.

Synthesis of MoIn2S4@CNTs Composite Counter Electrode for Dye-Sensitized Solar Cells.

A ternary and composite MoIn2S4@CNTs counter electrode (CE) with a hedgehog ball structure was synthesized by using a facile one-step hydrothermal method. The composite MoIn2S4@CNTs film possesses large specific surface area through N2 adsorption-desorption isotherms test, which is advantageous to adsorb more electrolyte and provide larger active contact area for the electrode. In addition, the composite MoIn2S4@CNTs CE exhibits low charge transfer resistance and fine electrocatalytic ability made from a series of electrochemical tests including cyclic voltammetry, electrochemical impedance, and Tafel curves. Under optimal conditions, the DSSC based on the MoIn2S4@CNTs-2 composite CE achieves an impressive power conversion efficiency as high as 8.38%, which remarkably exceeds that of the DSSCs with the MoIn2S4 CE (7.44%) and the Pt electrode (8.01%). The current work provides a simplified preparation process for the DSSCs.

Bis(µ-N,N-dimethyl-dithio-carbamato-κS,S':S)bis-[(N,N-dimethyl-dithio-carbamato-κS,S')copper(II)].

In the centrosymmetric dimeric title compound, [Cu(2)(C(3)H(6)NS(2))(4)], the Cu(II) atom is five-coordinate in a square-pyramidal environment. The basal coordination positions are occupied by four S atoms from two dimethyl-dithio-carbamate ligands and the apical coordination position is occupied by an S atom also bonded to the other Cu atom.

(N,N-Diethyl-dithio-carbamato-κS,S')iodido(1,10-phenanthroline-κN,N')copper(II).

The copper(II) atom in the title compound, [Cu(C(5)H(10)NS(2))I(C(12)H(8)N(2))], is chelated by the N-heterocycle and the dithio-carbamate anion in a slightly distorted tetragonal coordination. The tetragonal-pyramidal coorination is completed by the iodine atom in the apical position. One ethyl group is disordered over two positions with site occupancies of 0.31 (2) and 0.69 (2).

Iodido(1,10-phenanthroline-κN,N')(piperine-1-carbodithioato-κS,S')copper(II).

In the title compound, [Cu(C(6)H(10)NS(2))I(C(12)H(8)N(2))], the Cu(II) ion is coordinated by one iodide ion, two N atoms of the phenanthroline ligand and two S atoms from the piperidyl-dithio-carbamate ligand in a distorted square-pyramidal environment.

(2,2'-Bipyridine-κN,N')iodido(piperidine-1-carbodithio-ato-κS,S')copper(II).

In the title compound, [Cu(C(6)H(10)NS(2))I(C(10)H(8)N(2))], the Cu(II) ion is coordinated by one iodide ion, two N atoms of the bipyridine ligand and two S atoms from the piperidine-carbodithio-ate ligand in a distorted square-pyramidal environment. π-π stacking inter-actions, with centroid-centroid distances of 3.643 (4) Å, between pyridyl rings of the bipyridyl ligands of neighbouring mol-ecules lead to chains propagating parallel to the a axis.

(2,2'-Bipyridine-κN,N')iodido(pyrrol-idine-1-dithio-carboxyl-ato-κS,S')copper(II).

In the title compound, [Cu(C(5)H(8)NS(2))I(C(10)H(8)N(2))], the Cu(II) ion is coordinated by one iodide ion, two N atoms of the bipyridine ligand and two S atoms from the pyrrolidine-1-dithio-carboxyl-ate ligand in a distorted square-pyramidal environment.

Annealing-Free Cr2 O3 Electron-Selective Layer for Efficient Hybrid Perovskite Solar Cells.

The electron-selective layer (ESL) plays a pivotal role in the performance of perovskite solar cells (PSCs). In this study, amorphous dispersible chromium oxide (Cr2 O3 ) nanosheets are synthesized by a facile solvothermal reaction, and a Cr2 O3 ESL is prepared by spin-coating Cr2 O3 ink on fluorine-doped tin oxide substrates without need for further annealing. By using Cr2 O3 as the electron-selective layer and Cs0.05 (MA0.17 FA0.83 )0.95 Pb(I0.83 Br0.17 )3 as the light-absorption layer, a planar hybrid perovskite solar cell is fabricated. The spin-coating speed is optimized, the structure and morphology of samples are observed, the photoelectrical properties of ESLs are characterized, and the photovoltaic behaviors of devices are measured. Results show that the as-prepared Cr2 O3 layer has high optical transmittance and superb electron extraction and carrier transport property. The planar hybrid PSC based on the optimized Cr2 O3 ESL achieves a power conversion efficiency of 16.23 %, which is comparable to devices based on a conventional high-temperature-calcined TiO2 ESL. These results demonstrate a low-cost and facile route to highly effective perovskite solar cells.

Cadmium sulfide as an efficient electron transport material for inverted planar perovskite solar cells.

Dispersible cadmium sulfide (CdS) nanoparticles are synthesized by a facile solvothermal reaction and are used for the first time as an electron transport layer (ETL) in inverted planar perovskite solar cells. The CdS ETL has superb electron extraction and transport properties, leading to a solar cell with light hysteresis and a high efficiency of 13.36%.

Improved performance of a CoTe//AC asymmetric supercapacitor using a redox additive aqueous electrolyte.

Cobalt telluride (CoTe) nanosheets as supercapacitor electrode materials are grown on carbon fiber paper (CFP) by a facile hydrothermal process. The CoTe electrode exhibits significant pseudo-capacitive properties with a highest C m of 622.8 F g-1 at 1 A g-1 and remarkable cycle stability. A new asymmetric supercapacitor (ASC) is assembled based on CoTe (positive electrode) and activated carbon (negative electrode), which can expand the operating voltage to as high as 1.6 V, and has a specific capacitance of 67.3 F g-1 with an energy density of 23.5 W h kg-1 at 1 A g-1. The performance of the ASC can be improved by introducing redox additive K4Fe(CN)6 into alkaline electrolyte (KOH). The results indicate that the ASC with K4Fe(CN)6 exhibits an ultrahigh specific capacitance of 192.1 F g-1 and an energy density of 67.0 W h kg-1, which is nearly a threefold increase over the ASC with pristine electrolyte.

Hydrothermal Synthesis of Co-Doped NiSe2 Nanowire for High-Performance Asymmetric Supercapacitors.

Co@NiSe2 electrode materials were synthesized via a simple hydrothermal method by using nickel foam in situ as the backbone and subsequently characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and a specific surface area analyzer. Results show that the Co@NiSe2 electrode exhibits a nanowire structure and grows uniformly on the nickel foam base. These features make the electrode show a relatively high specific surface area and electrical conductivity, and thus exhibit excellent electrochemical performance. The obtained electrode has a high specific capacitance of 3167.6 F·g-1 at a current density of 1 A·g-1. To enlarge the potential window and increase the energy density, an asymmetric supercapacitor was assembled by using a Co@NiSe2 electrode and activated carbon acting as positive and negative electrodes, respectively. The prepared asymmetrical supercapacitor functions stably under the potential window of 0⁻1.6 V. The asymmetric supercapacitor can deliver a high energy density of 50.0 Wh·kg-1 at a power density of 779.0 W·kg-1. Moreover, the prepared asymmetric supercapacitor exhibits a good rate performance and cycle stability.

Nickel selenide/reduced graphene oxide nanocomposite as counter electrode for high efficient dye-sensitized solar cells.

Nickel selenide/reduced graphene oxide (Ni0.85Se/rGO) nanosheet composite is synthesized by a facile hydrothermal process and used as counter electrode (CE) for dye-sensitized solar cells (DSSC). The Ni0.85Se/rGO film spin-coated on FTO show prominent electrocatalytic activity toward I3-/I-. The electrocatalytic ability of Ni0.85Se/rGO film is verified by photocurrent-voltage curves, cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization curves. On account of its decent electrical conductivity and superior electrocatalytic activity, the DSSC using optimal Ni0.85Se/rGO CE achieves a power conversion efficiency (PCE) of 9.75%, while the DSSC based on sputtered Pt CE only obtains a PCE of 8.15%.