Ultraviolet-Visible-Short-Wavelength Infrared Broadband and Fast-Response Photodetectors Enabled by Individual Monocrystalline Perovskite Nanoplate.

Perovskite-based photodetectors exhibit potential applications in communication, neuromorphic chips, and biomedical imaging due to their outstanding photoelectric properties and facile manufacturability. However, few of perovskite-based photodetectors focus on ultraviolet-visible-short-wavelength infrared (UV-Vis-SWIR) broadband photodetection because of the relatively large bandgap. Moreover, such broadband photodetectors with individual nanocrystal channel featuring monolithic integration with functional electronic/optical components have hardly been explored. Herein, an individual monocrystalline MAPbBr3 nanoplate-based photodetector is demonstrated that simultaneously achieves efficient UV-Vis-SWIR detection and fast-response. Nanoplate photodetectors (NPDs) are prepared by assembling single nanoplate on adjacent gold electrodes. NPDs exhibit high external quantum efficiency (EQE) and detectivity of 1200% and 5.37 × 1012 Jones, as well as fast response with rise time of 80 µs. Notably, NPDs simultaneously achieve high EQE and fast response, exceeding most perovskite devices with multi-nanocrystal channel. Benefiting from the high specific surface area of nanoplate with surface-trap-assisted absorption, NPDs achieve high performance in the near-infrared and SWIR spectral region of 850-1450 nm. Unencapsulated devices show outstanding UV-laser-irradiation endurance and decent periodicity and repeatability after 29-day-storage in atmospheric environment. Finally, imaging applications are demonstrated. This work verifies the potential of perovskite-based broadband photodetection, and stimulates the monolithic integration of various perovskite-based devices.

Direct Surface Passivation of Perovskite Film by 4-Fluorophenethylammonium Iodide toward Stable and Efficient Perovskite Solar Cells.

Passivating the defective surface of perovskite films is becoming a particularly effective approach to further boost the efficiency and stability of their solar cells. Organic ammonium halide salts are extensively utilized as passivation agents in the form of their corresponding 2D perovskites to construct the 2D/3D perovskite bilayer architecture for superior device performance; however, this bilayer device partly suffers from the postannealing-induced destructiveness to the 3D perovskite bulk and charge transport barrier induced by the quantum confinement existing in the 2D perovskite. Hence, developing direct passivation of the perovskite layer by organic ammonium halides for high-performance devices can well address the above-mentioned issues, which has rarely been explored. Herein, an effective passivation strategy is proposed to directly modify the perovskite surface with an organic halide salt 4-fluorophenethylammonium iodide (F-PEAI) without further postannealing. The F-PEAI passivation largely inhibits the formation of the iodine vacancies and thus dramatically reduces the film defects, resulting in a much slower charge trapping process. Consequently, the F-PEAI-modified device achieves a much higher champion efficiency (21%) than that (19.5%) of the control device, which dominantly results from more efficient suppression of interfacial nonradiative recombination and the subsequent decreased recombination losses. Additionally, the F-PEAI-treated device maintains 90% of its initial efficiency after 720 h of humidity aging owing to the enhanced hydrophobicity and decreased trap states, highlighting good ambient stability. These results provide an effective passivation strategy toward efficient and stable perovskite solar cells.

Broadband Plasmonic Enhancement of High-Efficiency Dye-Sensitized Solar Cells by Incorporating Au@Ag@SiO2 Core-Shell Nanocuboids.

The introduction of plasmonic additives is a promising approach to boost the efficiency of the dye-sensitized solar cell (DSSC) since they may improve the light harvesting of a solar cell. Herein, we design broadband and strong plasmonic absorption Au@Ag@SiO2 nanocuboids (GSS NCs) as nanophotonic inclusions to achieve plasmon-enhanced DSSCs. These multiple-resonance absorptions arising from GSS NCs can be readily adjusted by altering their structures to complementarily match the absorption spectra of the dyes, especially in weak absorption zones. By subtly regulating the position of nanophotonic inclusions in the photoanodes, not only the plasmonic near-field enhancement but also far-field light scattering could be adequately developed to promote the light harvest and thus the efficiency of DSSCs. The resulting solar cells yield an average efficiency of 10.34%, with a champion value of 10.58%. The electromagnetic simulations are consistent with the experimental observations, further corroborating the synergistic effect of plasmonic improvement in these DSSCs.

Synthesis of Pt nanoparticles supported on a novel 2D bismuth tungstate/lanthanum titanate heterojunction for photoelectrocatalytic oxidation of methanol.

The combination of different semiconductors to form a heterojunction plays an important role for exploring new visible-light-driven electrocatalysts. Herein, a two-dimensional (2D) Bi2WO6/La2Ti2O7 (LTO) heterojunction has been synthesized and to be as carrier of Pt nanoparticles. Subsequently, electrocatalytic activity and stability of the as-obtained Pt-Bi2WO6/LTO has been evaluated in methanol oxidation reaction (MOR) under the action of visible light and electricity. Results indicate that Pt-Bi2WO6/LTO sample displays excellent catalytic performance and stability with assistance from visible light. Under identical conditions, the current intensity of MOR on the Pt-Bi2WO6/LTO modified electrode is found to reach 1409 mA mg-1Pt, which is 3.92 times higher than the measured Pt-Bi2WO6 modified electrode (359.8 mA mg-1Pt). In addition, the current density of MOR on Pt-Bi2WO6/LTO electrode decreases by 2.85% after scanning for 300 cycles. Furthermore, Pt-Bi2WO6/LTO is 6.99 times more resistant to poisoning than the Pt-Bi2WO6 electrode determines by chronopotentiometry under visible light illumination. The presented results indicate that a Pt-Bi2WO6/LTO nanocomposite is a viable alternative photo-electric catalyst, providing a potential new basis for the future development of catalysts in fuel cell reactions.

Highly efficient ethylene glycol electrocatalytic oxidation based on bimetallic PtNi on 2D molybdenum disulfide/reduced graphene oxide nanosheets.

In this paper, a two-dimensional (2D) hybrid material of molybdenum disulfide (MoS2)/reduced graphene oxide (RGO) is facilely synthesized and used as an ideal support for the deposition of Pt nanoparticles. The as-prepared Pt/MoS2/RGO composites are further worked as electrocatalysts towards ethylene glycol oxidation reaction (EGOR). In addition, when alloying with Ni, the composite shows obvious enhancement in electrocatalytic performance for EGOR. Specifically, the optimized molar ratio of Pt to Ni is 3:1, namely Pt3Ni/MoS2/RGO performs the strongest current density of 2062 mA mg-1Pt, which is 11.1, 5.80 and 2.40 times higher than those of Pt, Pt3Ni and Pt/MoS2/RGO electrodes, respectively. The systematically electrochemical measurements indicate that the largely promoted electrocatalytic performances of Pt3Ni/MoS2/RGO are mainly attributed to the synergistic effect of Ni and Pt, and 2D sheets of MoS2/RGO. This excellent performance indicates that the reported electrocatalytic material could be an efficient catalyst for the application in direct ethylene glycol fuel cell and beyond.

Facile fabrication of highly efficient ETL-free perovskite solar cells with 20% efficiency by defect passivation and interface engineering.

Tetramethylammonium hydroxide (TMAH) is employed to modify the surface and electrical properties of fluorine-doped tin oxide (FTO) electrodes in perovskite solar cells. Synchronously, owing to the flow of unbound TMA+ ions into the perovskite, the trap density of the perovskite overlayer is largely reduced. Conductivity of the grain boundaries in the perovskite layer is also greatly increased. A high efficiency of 20.1% along with a reduced J-V hysteresis in our champion perovskite solar cells without electron transport layers is achieved.

One-pot fabrication of Nitrogen-doped graphene supported binary palladium-sliver nanocapsules enable efficient ethylene glycol electrocatalysis.

Fuel cells hold great potential of replacing traditional fossil fuel to alleviate the energy crisis and increasing environmental concerns. Although great progresses have been achieved over decades, the sluggish reaction kinetics and poor durability of electrocatalysts in fuel cells have been the decisive bottleneck that limited their practical applications. Herein, we focus on the design and development of cost-efficient anode electrocatalysts for fuel cells and report the successful creation of an advanced class of N-doped graphene (NG) supported binary PdAg nanocapsules (PdAg NCPs). The well-defined nanocatalysts with highly open structure exhibit greatly improved electrocatalytic performances for ethylene glycol oxidation reaction (EGOR). In particular, the optimized PdAg NCPs/NG show the mass and specific activities of 6118.3 mA mg-1 and 13.8 mA cm-2, which are 5.8 and 6.9 times larger than those of the commercial Pd/C catalysts, respectively. More importantly, such PdAg NCPs/NG can also maintain at least 500 potential cycles with limited catalytic activity attenuation, showing an advanced class of electrocatalysts for fuel cells.

Transparent Indium Tin Oxide Electrodes on Muscovite Mica for High-Temperature-Processed Flexible Optoelectronic Devices.

Sn-doped In2O3 (ITO) electrodes were deposited on transparent and flexible muscovite mica. The use of mica substrate makes a high-temperature annealing process (up to 500 °C) possible. ITO/mica retains its low electric resistivity even after continuous bending of 1000 times on account of the unique layered structure of mica. When used as a transparent flexible heater, ITO/mica shows an extremely fast ramping (<15 s) up to a high temperature of over 438 °C. When used as a transparent electrode, ITO/mica permits a high-temperature annealing (450 °C) approach to fabricate flexible perovskite solar cells (PSCs) with high efficiency.

Organic-free Anatase TiO2 Paste for Efficient Plastic Dye-Sensitized Solar Cells and Low Temperature Processed Perovskite Solar Cells.

Recently, the synthesis of fine TiO2 paste with organic-free binder emerged as an indispensable technique for plastic photovoltaics due to the low temperature processing requirement. In this study, pure anatase TiO2 nanoparticles and organic-free TiO2-sol were successfully synthesized individually in organic-free solution. By mixing the pure anatase TiO2 with the newly developed TiO2-sol binder, mechanically robust and well-interconnected TiO2 films were prepared via UV-irradiation at low temperature for applications in plastic dye-sensitized solar cells (p-DSSCs). The structural, electrical, and photovoltaic properties of the films as well as the devices were investigated by various techniques. The dye-loading amount of the obtained film is 2.6 times that of the P25 electrodes. As revealed by electrochemical impedance spectroscopy results, the film derived from the as-prepared anatase TiO2 paste (A-TiO2) exhibits much smaller charge transport resistance and lower electron recombination rate than the P25 film, while the introduction of TiO2-sol into the paste can further remarkably decrease the resistance of the produced film (AS-TiO2). The p-DSSCs employing AS-TiO2 photoanode yield a high efficiency up to 7.51%, which is 86% higher than the P25 reference cells and also 31% higher than the A-TiO2 cell. As a proof of concept, the newly developed AS-TiO2 paste was also applied to low temperature processed perovskite solar cells (PSCs), and a promising high efficiency up to 9.95% was achieved.

Facile one-step synthesis of highly branched ZnO nanostructures on titanium foil for flexible dye-sensitized solar cells.

Highly branched ZnO (HBZ) nanostructures were prepared on titanium (Ti) foil using a facile, one-step vapor confined chemical vapor deposition technique. The as-prepared ZnO layer showed a good connection with the Ti foil even after 50 bending cycles, and the resultant HBZ/Ti electrode possessed high bendability. The HBZ/Ti electrode was composed of four different layers, including a highly branched ZnO layer, a ZnO compact layer, a Ti-Zn alloy layer and Ti foil. The good adhesion of the as-prepared ZnO layer to Ti foil was ascribed to the formation of a Ti-Zn alloy layer and a ZnO compact layer during the growth process. A flexible dye-sensitized solar cell was assembled using the D149-sensitized HBZ/Ti as a photoanode, and a power conversion efficiency (PCE) of 3.3% was achieved with an open-circuit photovoltage of 0.664 V, a short-circuit current density of 7.53 mA cm(-2), and a fill factor of 0.66 measured under rear-side illumination (AM 1.5, 100 mW cm(-2)). The power conversion efficiency of the device remained at 92% of the initial value even after 50 bending cycles. These results indicate that the vapor confined chemical vapor deposition method which does not necessarily use any catalyst or seed is a facile, one-step approach to obtain highly branched ZnO nanostructures with high bendability on Ti foil. The tight bonding between the highly branched ZnO layer and Ti substrate by a Ti-Zn alloy layer and a ZnO compact layer makes the vapor confined CVD method very attractive for the preparation of high-performance flexible photoanodes.

Facile synthesis of poly(3,4-ethylenedioxythiophene) film via solid-state polymerization as high-performance Pt-free counter electrodes for plastic dye-sensitized solar cells.

A high-performance Pt-free counter electrode (CE) based on poly(3,4-ethylenedioxythiophene) (PEDOT) film for plastic dye-sensitized solar cells (DSCs) has been developed via a facile solid-state polymerization (SSP) approach. The polymerization was simply initiated by sintering the monomer, 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT), at the temperature of 80 °C, which can be applied on the plastic substrate. The cyclic voltammetry measurements revealed that the catalytic activity of the SSP-PEDOT CE for triiodide reduction is comparable with that of the Pt CE. Under optimized conditions, the power conversion efficiency of a DSC with a N719-sensitized TiO2 photoanode and the SSP-PEDOT CE is 7.04% measured under standard 1 sun illumination (100 mW cm(-2), AM 1.5), which is very close to that of the device fabricated under the same conditions with a conventional thermally deposited Pt CE (7.35%). Furthermore, taking advantage of the compatibility of the SSP-PEDOT with the plastic substrates, a full plastic N719-sensitized TiO2 solar cell was demonstrated, and an efficiency of 4.65% was achieved, which is comparable with the performance of a plastic DSC with a sputter-deposited Pt CE (5.38%). These results demonstrated that solid-state polymerization initiated at low temperature is a facile and low-cost method of fabricating the high-performance Pt-free CEs for plastic DSCs.

High-performance plastic platinized counter electrode via photoplatinization technique for flexible dye-sensitized solar cells.

A photoplatinization technique was proposed to deposit Pt on a thin TiO(2) layer modified indium tin oxide-coated polyethylene naphthalate (ITO/PEN) substrate at low temperature (about 50 °C after 1 h of UV irradiation) for the first time. The fabrication process includes coating and hydrolyzing the tetra-n-butyl titanate to form a TiO(2)-modified layer and the photoplatinization of the modified substrate in H(2)PtCl(6)/2-propanol precursor solution under UV irradiation. The obtained platinized electrodes were used as counter electrodes (CE) for flexible dye-sensitized solar cells (FDSCs). The well-optimized platinized electrode showed high optical transmittance, up to 76.5% between 400 and 800 nm (T(av)), and the charge transfer resistance (R(ct)) was as low as 0.66 Ω cm(2). A series of characterizations also demonstrated the outstanding chemical/electrochemical durability and mechanical stability of the platinized electrode. The FDSCs with TiO(2)/Ti photoanodes and the obtained CEs achieved a power conversion efficiency (PCE) up to 8.12% under rear-side irradiation (AM 1.5 illumination, 100 mW cm(-2)). The obtained CEs were also employed in all-plastic bifacial DSCs. When irradiated from the rear side, the bifacial FDSC yielded a PCE of 6.26%, which approached 90% that of front-side irradiation (6.97%). Our study revealed that, apart from serving as a functional layer for deposition of Pt, the thin TiO(2) layer modification on ITO/PEN substrates also played an important role in improving the transparency and the mechanical properties of the CE. The effect of the thickness of the TiO(2) layer for Pt coating on the performance of the CE was also investigated.