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Although the efficiency of perovskite solar cells is over 25%, there is still a big difference between the open-circuit voltage and its theoretical value, which is ascribed to defects in the perovskite films.

Traditional P-i-N perovskite solar cells have achieved high efficiency over 25%, but the device structure is relatively complex, and generally requires expensive low-conductivity p-type organic semiconductors as hole transport materials. As a typical semiconductor, it is very important to realize the bipolar doping of methylamine lead iodine (CH3NH3PbI3) that is the light-absorbing layer of perovskite solar cell. Also, it is significant to develop perovskite cells with new device structure. Here, we chose lithium iodide (LiI) as the dopant and successfully grow p-type Li+ doped CH3NH3PbI3 (MAPbI3:Li) perovskite films with low resistivity (103 Ω•cm). The temperature-dependent photoluminescence, Hall effect and Kelvin probe force microscope (KPFM) results strongly confirmed that Li+ doping promotes the transformation of pristine weak n-type MAPbI3 to intentionally doped p-type film. Subsequently, the p-type MAPbI3 film is used as both the light absorption layer and hole transport layer, and form a PN heterojunction with n-type titanium dioxide (TiO2), which is used as the electron transport layer, to construct the heterostructural perovskite cell with a photoelectric conversion efficiency (PCE) of 10.43%. The electron beam induced current (EBIC) signal also strongly confirms the existence of the PN heterojunction and the new working mechanism of such new solar cells.

Improvements in the light-harvesting capacity and the carrier extraction are both significant to improve the photovoltaic performance of perovskite solar cells (PSCs). It has been proved that local...

Passivating defects to suppress recombination is a valid tactic to improve the performance of third-generation perovskite-based solar cells. Pb0 is the primary defect in Pb-based perovskites. Here,...

Perovskite solar cells (PSCs) have attracted considerable attention as a prominent photovoltaic technology, yet the state-of-the-art PSCs still contain thermally unstable methylammonium (MA) cation...

In this report, cobalt telluride (CoTe) is synthesized in a water-oil heterogeneous system, and CoTe film fabricated by spin-coating method is applied as platinum (Pt) -free counter electrode for dye-sensitized solar cells. Field emission scanning electron microscopy finds that CoTe counter electrode exhibits porous structure. Cyclic voltammogram and electrochemical impedance spectroscopy demonstrate that CoTe has admirable electro catalytic activity toward the reduction of triiodide. The dye-sensitized solar cell based on CoTe counter electrode obtains a power conversion efficiency of 8.59%, which is higher than that with conventional platinum (Pt) counter electrode (8.19%). The impressive efficiency along with simple preparation of CoTe highlights the potential substitute for conventional noble metal Pt.

The introduction of upconversion materials as spectral converter into photovoltaic devices to harvest and convert near infrared photons to visible photons that can thus be absorbed by perovskite layer is a promising strategy for enhancing the performance of perovskite solar cells. Hence, β-NaYF4:Yb3+/Er3+/Sc3+@NaYF4 rare-earth doped upconversion nanoparticles with core-shell structure are synthesized. The doped rare-earth ions Yb3+ and Er3+ convert near infrared light to red and green light, and the Sc3+ ions enhance the upconversion luminescence efficiency, which broaden the absorption range of solar irradiation and generate extra photocurrent in the solar cells. The surface defects of β-NaYF4:Yb3+/Er3+/Sc3+ is passivated by the even NaYF4 shell, which results in the obvious enhancement in upconversion emission intensity. Consequently, the perovskite solar cell based on the rare-earth doped upconversion nanoparticle mesoporous layer achieves a high power conversion efficiency of 20.19%, while the device based on TiO2 mesoporous layer gets an efficiency of 17.44%.

Organic–inorganic hybrid halide perovskite solar cells have attracted considerable attention owing to their high power conversion efficiency. Up to now, anti-solvent assisted one-step spin-coating crystallization method is still a major process to achieve high quality perovskite film. However, the toxicity of commonly used anti-solvents and the nonrepeatability of corresponding solar cell still obstruct the potential of commercial applications. Here, high-quality perovskite film, fabricated with anti-solvent engineering, is successfully developed by using a green mixed anti-solvent of ethylacetate with isopropanol as additive. Compared with pure ethylacetate anti-solvent, the mixed anti-solvent can significantly improve the surface morphology and passivate the grainboundary/surface defects of perovskite film, distinctly enhancing the photovoltaic property and the repeatability of P-i-N planar devices. The best-performing device exhibits a remarkable efficiency of 18.98% with negligible hysteresis and praiseworthy stability over 30 days in dry conditions. Our findings provide an avenue for high efficiency and stable planar perovskite devices with low cost and environmental-friendly manufacturing.

Perovskite solar cells assembled with titanium dioxide electron transport layer exhibited brilliant photovoltaic properties due to titanium dioxide having a high electron mobility, appropriate energy level alignment and easy fabrication procedure. However, inherent instability exists in titanium dioxide-based perovskite solar cells because of the ultraviolet photocatalytic activity of titanium dioxide. This results in recombination at the interface of titanium dioxide/perovskite. In this report, the down-conversion nanocrystals film made of europium-doped sodium yttrium fluoride was deposited on the non-conducting side of the conducting glass. The down-conversion nanocrystal layer could absorb high energy ultraviolet photons and converted them to visible light. The layer not only extended the spectral response range for perovskite solar cells but also alleviated the photocatalytic activity of titanium dioxide. The perovskite solar cells with the down-conversion nanocrystals film generated average power conversion efficiency yield of 19.99%, which is much better than that of the device without the down-conversion nanocrystals film (16.99%). The best power conversion efficiency for the device with the down-conversion nanocrystals film was 20.17%. In addition, perovskite solar cells with the down-conversion nanocrystals film showed a small hysteresis.

A hollow rod-like hybrid of Co2CrO4/Co1−xS is synthesized via a facile two-step hydrothermal process, and the mass ratio for Co2CrO4–Co1−xS in the hybrid is optimized. The Co2CrO4/Co1−xS electrode exhibits excellent properties with high specific capacitance of 1580 F g−1 at current density of 1 A g−1 and possesses good rate performance. An asymmetric supercapacitor of Co2CrO4/Co1−xS//AC is assembled, which can be operated within a voltage range of 0–1.6 V, demonstrating specific capacitance of 92.3 F g−1, energy density of 32.8 Wh kg−1 and highest power density of 4003.3 W kg−1. Moreover, the specific capacitance of the device remains 88% after 5000 cycles. The good characteristics of Co2CrO4/Co1−xS//AC can be ascribed to the hollow rod-like structure and the positive synergistic effects of Co2CrO4 and Co1−xS components in the hybrid. The unique structure and superior performances render Co2CrO4/Co1−xS hybrid as a promising candidate for energy storage device.

Cobalt molybdate/non-stoichiometric cobalt sulfide (CoMoO4/Co1−xS) hybrid was in situ grown on nickel foam by a simple two-step hydrothermal process. The as-prepared CoMoO4/Co1−xS hybrid electrode possessed core-shell nanostructure, large surface area and high specific capacitance of 2250 F g−1 at a current density of 1 A g−1. Using the hybrid as anode and activated carbon (AC) as cathode, an asymmetric supercapacitor of CoMoO4/Co1−xS//AC was fabricated. The optimized supercapacitor had large potential window of 1.6 V and high capacitance of 112 F g−1, resulting in high power density of 804.5 W kg−1 and energy density of 39.8 Wh kg−1. Furthermore, the supercapacitor exhibited an excellent long cycle life along with 86.4% specific capacitance retained after 5000 cycles. The superior performances and good stability of the asymmetric supercapacitor can be attributed to the unique structure of the two components in hybrid, and the positive synergistic effects of the hybrid electrodes. The facile preparation process and excellent performance presented here render the CoMoO4/Co1−xS hybrid as a promising candidate for energy storage device.

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.

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%.

Overcoming the toxicity of organic–inorganic perovskite materials is one of the main challenges in applying them to commercial optoelectronic devices, despite the amazing power conversion efficiency (PCE) of organic–inorganic hybrid perovskite solar cells (PSCs). In this work, we demonstrate a low-toxicity Pb-Cu alloyed perovskite film prepared by simple two-step methods and its integration in inverted PSCs. The formation of iodine defects was suppressed through the hydrogen bonding of guanidinium (Gua) cation (CH6N3+), which greatly improves the quality of the film. It is demonstrated that introduction of GuaI additives leads to stronger photoluminescence (PL) intensity, and lower defects state density. The open circuit voltage (Voc) and PCE of Pb-Cu alloyed PSCs reached 0.95 V and 9.69%, respectively. This work helps to guide the preparation of efficient low-toxicity Pb-Cu alloyed optoelectronic devices.

Owing to the advantages of portability and flexibility, flexible perovskite solar cells have broad application prospects in the fields of portable wearable electronics and photovoltaic buildings. However, high temperature annealing process is often needed to improve the crystallinity and electron transport properties for electron transport layer, which restricts the development of flexible perovskite solar cells. In this work, well crystalline and monodisperse SnO2 nanocrystals are synthesized by facile solvothermal method with the assistance of oleic acid molecules. However, the presence of oleic acid molecules blocks the transportation of photogenerated electrons on account of the insulation of oleic acid molecules. To address the problem, the oleic acid ligands are ulteriorly peeled off by ligand exchange technique. Surprisingly, the resulted SnO2 electron transport layer exhibits superior electron extraction and transport capacity. The final power conversion efficiency comes to 17.96% from 13.71%.

A flexible electrode of nickel diselenide/carbon fiber cloth (NiSe 2 /CFC) is fabricated at room temperature by a simple and efficient electrodeposition method. Owing to NiSe 2 character of nanostructure and high conductivity, the as-synthesized electrodes possess perfect pseudocapacitive property with high specific capacitance and excellent rate capability. In three-electrode system, the electrode specific capacitance of the NiSe 2 /CFC electrode varies from 1058 F g -1 to 996.3 F g -1 at 2 A g -1 to 10 A g -1 respectively, which shows great rate capability. Moreover, the NiSe 2 electrode is assembled with an active carbon (AC) electrode to form an asymmetric supercapacitor with an extended potential window of 1.6 V. The asymmetric supercapacitor possesses an excellent energy density 32.7 Wh kg -1 with a power density 800 W kg -1 at the current density of 1 A g -1 . The nanosheet array on carbon fiber cloth with high flexibility, specific capacitance and rate capacitance render the NiSe 2 to be regarded as the promising material for the high performance superconductor.

CuI, as a promising hole transport material, possesses high hole mobility and is compatible with perovskite materials about band structure. Herein, CuI hole transport films are first fabricated by vacuum thermal evaporation procedure for n-i-p perovskite solar cell. The results show that vacuum thermal evaporated CuI films have no obvious influence on perovskite underlayer and 200 nm thick CuI film has the best carrier extraction ability. To further improve the stability of the device, reduced graphene oxides are introduced to avoid the accelerated attenuation caused by the reaction of CuI with Au. Finally, the power conversion efficiency of the dual-modified device improves to 8.69%, with the short circuit current density of 18.86 mA cm−2, the open circuit voltage of 0.832 V and the filling factor of 0.550. The work demonstrates a potential application of vacuum thermal evaporated CuI films in organic-inorganic hybrid perovskite solar cells.

Electron transport layer (ETL) plays an important role in improving charge transportation, suppressing current-voltage hysteresis and enhancing photovoltaic performance of perovskite solar cells (PSCs). Here we successfully synthesize anatase titania nanoparticles (TiO2 NPs) with an average diameter about 3.6 nm by a facile and low-cost solvothermal method. Using the as-synthesized TiO2 NPs as ETL, the planar perovskite solar cells exhibit good photovoltaic performance. Encouragingly, when the TiO2 NPs are modified with titanium acetylacetonate [TiO(acac)2], a pinhole-free, dense, low charge transfer resistance and high charge extraction TiO2 ETL is formed and the power conversion efficiency of the planar perovskite solar cell is enhanced from 17.25% to 19.21%, accompanied by a significant decrease of J-V hysteresis. The facile process and significant performance improvement suggest that acetylacetonate modified TiO2 nanoparticles could be good ETL candidates for high-performance planar perovskite solar cells with low hysteresis.

Cobalt diselenide (CoSe2) is endowed with excellent and stable photoelectrochemical properties. However, the preparations of CoSe2 usually need high pressure, high temperature, long reaction time or special devices. Here, CoSe2 counter electrodes are prepared by a facile electrochemical deposition method and controlling different deposition voltage. The influence of deposition voltage on the film quality and the performance of dye-sensitized solar cells is investigated, and the CoSe2 counter electrode with –1.1 V deposition voltage achieve a best power conversion efficiency of 10.17%, which has a 21.9% increase compared to the solar cell based on platinum counter electrode (8.35%). The impressive efficiency together with facile preparation highlights the potential for substitute for the noble metal platinum.

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%.

Nickel selenide (Ni0.85Se) was synthesized by a facile one-step hydrothermal reaction and Ni0.85Se film was prepared by spin-coating Ni0.85Se ink on FTO and used as counter electrode (CE) in dye-sensitized solar cells (DSSC). The Ni0.85Se CEs not only show high transmittance in visible range, but also possess remarkable electrocatalytic activity toward I−/I3−. The electrocatalytic ability of Ni0.85Se films was verified by cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization curves. The DSSC using Ni0.85Se CE exhibits a power conversion efficiency (PCE) of 8.96%, while the DSSC consisting of sputtered Pt CE only exhibits a PCE of 8.15%. When adding a mirror under Ni0.85Se CE, the resultant DSSC exhibits a PCE of 10.76%, which exceeds that of a DSSC based on sputtered Pt CE (8.44%) by 27.49%.

In this report, redispersable CdS nanoparticles are synthesized via a specific one-step solvothermal reaction and are employed as electron-selective materials for organometal halide perovskite solar cells. The as-synthesized CdS nanoparticles can be well re-dispersed in toluene to form a uniform and stable CdS ink. On this basis, a CdS electron-selective contact layer can be directly prepared by spin-coating CdS ink and without a further annealing process. The CdS electron-selective contact layer has high optical transmittance at visible wavelengths. Its electron extraction and transfer properties are also investigated using current density–voltage curves, incident photocurrent conversion efficiency, stabilized current density and photoluminescence spectra. The use of a CdS electron-selective contact layer in a planar perovskite solar cell equipped with a Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3 light-absorption layer results in a high power conversion efficiency of 16.5%.

Cobalt selenite dihydrate (CoSeO 3 ·2H 2 O) is spin-coated on conductive glass and used as counter electrode (CE) in dye-sensitized solar cells (DSSCs). Owing to CoSeO 3 ·2H 2 O electrode good electrocatalytic activity, high conductivity and low resistance, the DSSC based on optimal CoSeO 3 ·2H 2 O CE provides a power conversion efficiency of 8.90% under one sun irradiation from the front of DSSC, which is superior to the DSSC based on conventional Pt CE. Furthermore, when incorporating trace amounts of reduced graphene oxide (rGO) into CoSeO 3 ·2H 2 O CE, the DSSC device achieves an improved power conversion efficiency of 9.89%. The research presented here indicates that hydration oxysalt can be used as efficient, stable and free-Pt counter electrode material and shows excellent prospects for application in DSSCs.

A TiO 2 compact layer is crucial to a high-performance perovskite solar cell (PSC). Interestingly, there is a severe paucity of research on using one-dimensional nanostructure to fabricate the compact layer. In this study, anatase TiO 2 single-crystalline nanorods (NRs) with a length of 30 ± 10 nm and a diameter of 4 ± 1 nm are synthesized via a one-pot solvothermal approach. A pinhole-free and thickness-controllable compact layer on PSC is fabricated by spin-coating the TiO 2 nanorods on transparent conductive oxide substrate. Thanks to good electronic transport channel and less defects and interfaces, one-dimensional TiO 2 NRs, with longer electron lifetime, shorter transport time and higher charge collection efficiency than TiO 2 quantum dots (QDs) and TiO 2 nanoparticles (NPs), can improve the photovoltaic performance of the PSC based on TiO 2 -NR compact layer. As a result, the PSC based on TiO 2 NRs shows the best photovoltaic performance with a power conversion efficiency of 17.58%, which is enhanced by a factor of 1.16 and 1.30 respectively compared with the PSCs based on TiO 2 -QDs and TiO 2 -NPs.

Tin oxide (SnO 2 ), as electron transport material to substitute titanium oxide (TiO 2 ) in perovskite solar cells (PSCs), has aroused wide interests. However, the performance of the PSCs based on SnO 2 is still hard to compete with the TiO 2 -based devices. Herein, a novel strategy is designed to enhance the photovoltaic performance and long-term stability of PSCs by integrating rare-earth ions Ln 3+ (Sc 3+ , Y 3+ , La 3+ ) with SnO 2 nanospheres as mesoporous scaffold. The doping of Ln promotes the formation of dense and large-sized perovskite crystals, which facilitate interfacial contact of electron transport layer/perovskite layer and improve charge transport dynamics. Ln dopant optimizes the energy level of perovskite layer, reduces the charge transport resistance, and mitigates the trap state density. As a result, the optimized mesoporous PSC achieves a champion power conversion efficiency (PCE) of 20.63% without hysteresis, while the undoped PSC obtains an efficiency of 19.01%. The investigation demonstrates that the rare-earth doping is low-cost and effective method to improve the photovoltaic performance of SnO 2 -based PSCs.

Expanding the solar spectral response near-infrared wave range is undoubtedly an important strategy that can enhance the power conversion efficiency of perovskite solar cells. While, the up-conversion nanoparticles with only one sensitizer to absorb near-infrared photons cannot meet the needs. Hence, NaYF4:Nd3+/Yb3+/Er3+ rare earth doped up-conversion nanoparticles with dual-sensitizers are synthesized. By doping rare earth ions Nd3+, Yb3+ and Er3+, the photocurrent density of perovskite solar cells is increased from 20.87 mA cm−2 to 22.74 mA cm−2, and the power conversion efficiency is increased from 17.95% to 19.23%, an improvement of 7.13% compared with reference device.

Organic-inorganic lead halide perovskite solar cell is on the spotlight due to its low fabrication cost and excellent optoelectronic properties. SnO2 is considered as a promising alternative for TiO2 as the electron transport layer due to its high charge mobility. Here we report on a combustion method to prepare high-performance SnO2 extraction layer. Compared to SnO2 from the conventional solution-processed method, this SnO2 layer has a faster ability to extract and transfer the photoelectron. The device based on SnO2 from combustion method obtains a power conversion efficiency of 19.12%, which has a 24.8% increase compared to the device based on SnO2 from the conventional method. Further adding Nd3+ ion to the SnO2, the PCE comes to 20.92%.

In this Letter, we report the polarization-enhanced bulk photovoltaic effect (BPV) in pristine BiFeO3 (BFO) epitaxial film under standard 1 sun AM 1.5 G illumination. High-quality epitaxial BFO films are grown on (001)-oriented niobium doped-SrTiO3 substrates by pulsed laser deposition. The best BFO film based photovoltaic device achieves a power conversion efficiency of 0.0062% under standard illumination. Besides, it is found that the number of bipolar pulses plays a key role in improving the short-circuit current density and open-circuit voltage. These results are beneficial for further understanding of physical origin of the photovoltaic properties in ferroelectric oxides.

Metal dichalcogenide has a layered structure, which is endowed with versatile and tunable photoelectrochemical properties. In this paper, molybdenum diselenide (MoSe2) is synthesized by the solvothermal method, and the as-synthesized MoSe2 shows microsphere hierarchical architecture composed of 2-D nanosheets. The electrochemical characterization indicates that the MoSe2 electrode has lower resistances and better electrocatalytic activity toward triiodide/iodide redox reaction than the traditional Pt electrode. Using the MoSe 2 as a counter electrode in the dye-sensitized solar cell (DSSC), a high-power-conversion efficiency of 9.80% is achieved, outperforming the DSSC-based traditional Pt counter electrode (8.17%). Moreover, using the MoSe2 as an electrode in the supercapacitor, it displays a high specific capacitance of 272 F⋅g−1.

3,4-Ethylenedioxy thiophene (EDOT) precursor solution doped by Fe3O4 was spin-casted onto fluorine doped tin oxide (FTO) glass and formed poly(3,4-ethylenedioxy thiophene) (PEDOT)/Fe3O4 hybrid films by an in situ polyreaction. The films were utilized as the counter electrode in dye sensitized solar cells (DSSCs). Photoelectric conversion efficiency (PCE) for DSSCs based on PEDOT/Fe3O4 varied with the content of Fe3O4 in the precursor solution. When the content of Fe3O4 was 2 mg ml−1 in the precursor solution (PEDOT/Fe3O4-2), the best performance (8.69%) was obtained. In comparison, that of a DSSC with a Pt counter electrode is 8.35%. According to the surface microtopography and electrochemical analysis, large active areas, consecutive electronic transmission channels and lower charge transfer resistance could be responsible for the high PCE.

Cobalt selenide/molybdenum selenide/molybdenum oxide (Co 0.85 Se/MoSe 2 /MoO 3 ) ternary hybrid is synthesized by a facile hydrothermal method and used as efficient Pt-free counter electrode (CE) for dye-sensitized solar cells (DSSCs). Field emission scanning electron microscopy observes that Co 0.85 Se/MoSe 2 /MoO 3 possesses hierarchical architecture with one-dimensional (1D) nanorods, two-dimensional (2D) nanosheet and three-dimensional (3D) nanoparticle. Cyclic voltammogram indicates that Co 0.85 Se/MoSe 2 /MoO 3 hybrid have larger current density than sputtered Pt electrode. Electrochemical impedance spectroscopy shows that cooperation among Co 0.85 Se, MoSe 2 and MoO 3 reduces series resistance and charge transfer resistance. The DSSC based on Co 0.85 Se/MoSe 2 /MoO 3 CE achieves a power conversion efficiency of 7.10%, which is higher than that of the DSSC based on sputtered Pt CE (6.03%).

A cobalt telluride/reduced graphene oxide (CoTe/RGO) hybrid is synthesized by hydrothermal method and used as counter electrode in dye-sensitized solar cell (DSSC). The synthesized samples are characterized by field emission scanning electron microscopy and transmission electron microscope, which shows that CoTe/RGO has a larger specific surface area than CoTe. Cyclic voltammogram measurement indicates that CoTe/RGO electrode has larger current density and better electrocatalytic activity in the reduction of triiodidie than Pt electrode. Electrochemical impedance spectroscopy shows that CoTe/RGO electrode has lower charge-transfer resistance (2.94 Ω cm2). Owing to above advantages, the DSSC based on CoTe/RGO counter electrode achieves a high power conversion efficiency of 9.17%, outperforming that based on Pt counter electrode (8.17%). Therefore, inexpensive CoTe/RGO is a promising counter electrode to replace noble metal Pt.

Lithium-sulfur batteries are regarded as next generation energy storage systems because of their high theoretical specific capacity and low cost. However, the polysulfide shuttle effect, low electronic conductivity of sulfur/lithium sulfides and slow redox kinetics of polysulfide conversion still limit their practical application. Herein, we design a hollow nanosphere structure with CeO2 shell/ultrathin nitrogen-doped carbon shell as highly efficient sulfur host for lithium-sulfur batteries. The unique structure not only offers physical entrapment for sulfur species by CeO2/carbon shells, but also provides strong chemical adsorption and activation sites for chemical adsorption and catalytic conversion of polysulfides through CeO2 nanoparticles. Moreover, the unique hollow structure offers enough space for volume variations of sulfur during charge/discharge process and facilitates fast electron/ion transport to continuously activate active material, therefore improving the electrochemical performances of lithium-sulfur batteries. By combining these advantages, the obtained NC@H-CeO2/S cathodes exhibit high reversible capacity (1348 mAh g−1 at 0.2 C), excellent rate capability (548 mAh g−1 at 5 C) and superior cycle stability (632 and 458 mAh g−1 at 2 and 5 C after 500 cycles, respectively). Moreover, the cathodes with high sulfur loading of 3.5 mg cm−2 remain excellent rate capability and cycling stability. This work provides a new strategy to the design of advanced cathode materials for high-performance lithium-sulfur batteries.

In perovskite solar cells, the interface plays a critically important role in photovoltaic performance as the exciton dissociation and recombination occur here. In this report, In2O3 is developed as an efficient interlayer between TiO2 electron-transporting layer and perovskite light-absorption layer in planar perovskite solar cells. The modification of In2O3 interlayer results in a superb enhancement in average power conversion efficiency (from 16.71% to 18.93%). Meanwhile, the hysteresis phenomenon gets prominently improved. Based on this background, some other characterizations are performed. The results reveal that the improved photovoltaic performance through depositing In2O3 interlayer can be ascribed to better film morphology, decreased recombination center, improved conductivity, reduced trap-state density and enhanced electron extraction capacity. This study demonstrates that In2O3 can be an efficient interfacial material for TiO2-based perovskite solar cells.

Cobalt selenide/tin selenide (CoSe/SnSe) hybrid is successfully synthesized via a facile solvothermal method and used as an efficient Pt-free counter electrode (CE) for dye-sensitized solar cells (DSSCs). Field emission scanning electron microscopy observes that CoSe/SnSe hybrid is made up of nanosheets and nanoparticles; the nanosheets are CoSe, while the nanoparticles are SnSe. Cyclic voltammogram measurement indicates that CoSe/SnSe hybrid electrodes have larger current density than CoSe electrode and Pt electrode. Electrochemical impedance spectroscopy shows that the 3CoSe/SnSe hybrid has low charge-transfer resistance of 1.03 Ω cm2. Under simulated solar light irradiation with intensity of 100 mW cm−2 (AM 1.5), the DSSC based on the Co3SnSe4 hybrid CE achieves a power conversion efficiency of 7.71 %, which is higher than that the DSSC based on conventional Pt CE (6.89 %). The DSSCs with all as-prepared CoSe/SnSe hybrid CEs exhibit better photovoltaic performance than the DSSC with conventional Pt CE.

A transparent nickel selenide (Ni 0.85 Se) is prepared by a facile solvothermal reaction and used as an efficient Pt-free counter electrode (CE) for dye-sensitized solar cells (DSSCs). Field emission scanning electron microscopy observes that the as-prepared Ni 0.85 Se possesses porous structure. Cyclic voltammogram measurement indicates that Ni 0.85 Se electrode has larger current density than Pt electrode. Electrochemical impedance spectroscopy shows that the Ni 0.85 Se electrode has lower charge-transfer resistance than Pt electrode. Under simulated solar light irradiation with intensity of 100 mW cm −2 (AM 1.5), the DSSC based on the Ni 0.85 Se CE achieves a power conversion efficiency (PCE) of 8.88%, which is higher than the solar cell based on Pt CE (8.13%). Based on the transparency of Ni 0.85 Se, the DSSC with Ni 0.85 Se/mirror achieves a PCE of 10.19%.

Cobalt selenide (CoSe 2 ) nanorods are prepared by hydrothermal method and used as an efficient Pt-free counter electrode (CE) for dye-sensitized solar cells (DSSCs). Field emission scanning electron microscopy observes that CoSe 2 mostly exhibits a nanorod morphology, which facilitates change carrier transfer from their surface to redox electrolyte. Cyclic voltammogram measurement indicates that CoSe 2 electrode has larger current density than Pt electrode. Electrochemical impedance spectroscopy shows that the CoSe 2 electrode with optimal condition has low series resistance of 8.034 Ω × cm 2 and has low charge-transfer resistance of 0.097 Ω·cm 2 . Under simulated solar light irradiation with intensity of 100 mW·cm −2 (AM 1.5), the DSSC based on the CoSe 2 CE achieves a power conversion efficiency of 8.38 %, which is higher than the solar cell based on Pt CE (7.83%).

The electron-selective layer (ESL) plays a pivotal role in the performance of perovskite solar cells (PSCs). In this study, amorphous dispersible chromium oxide (Cr

The organic-inorganic lead halide perovskite layer is a crucial factor for the high performance perovskite solar cell (PSC). We introduce CH3NH3Br in the precursor solution to prepare CH3NH3PbI3−xBrx hybrid perovskite, and an uniform perovskite layer with improved crystallinity and apparent grain contour is obtained, resulting in the significant improvement of photovoltaic performance of PSCs. The effects of CH3NH3Br on the perovskite morphology, crystallinity, absorption property, charge carrier dynamics and device characteristics are discussed, and the improvement of open circuit voltage of the device depended on Br doping is confirmed. Based on above, the device based on CH3NH3PbI2.86Br0.14 exhibits a champion power conversion efficiency (PCE) of 18.02%. This study represents an efficient method for high-performance perovskite solar cell by modulating CH3NH3PbI3−xBrx film.

Iron objects excavated from the Dongheishan site provided a chance to systematically study the iron and steel making technology during the Warring States period and the Han dynasty in the Yan region, north China. According to the results of radiocarbon dating, metallographic and slag inclusions analysis, it was found that they were made of cast iron or cast iron subsequently processed into steel, and most radiocarbon dates of iron artefacts were consistent with the determination from their archaeological context. The technology in this region was as advanced as the Central Plain China, and it was probably a previously unknown centre of technological innovation during this period. Meanwhile, the results showed that the local craftsmen used different types of iron and steel and different technologies to produce different types of objects.