Compositional Engineering of Hybrid Organic-Inorganic Lead-Halide Perovskite and PVDF-Graphene for High-Performance Triboelectric Nanogenerators.

Triboelectric nanogenerators (TENGs) have attracted a great deal of attention since they can convert ubiquitous mechanical energy into electrical energy and serve as a continuous power source for self-powered sensors. Optimization of the dielectric material composition is an effective way to improve the triboelectric output performance of TENGs. Herein, the hybrid organic-inorganic lead-iodide perovskite Cs0.05FA0.95-xMAxPbI3 was prepared by blade coating and used as a positive friction layer material. Moreover, PVDF-graphene (PG) nanofibers were prepared as negative friction layer materials by electrostatic spinning. The output performance of the TENG was enhanced by varying the MA content of the pervoskite films and the graphene content of the PG nanofibers. The champion output TENG based on Cs0.05FA0.9MA0.05PbI3/PG-0.15 achieved an open-circuit voltage of 245 V, a short-circuit current of 24 µA, and a charge transfer of 80.2 nC. Meanwhile, a maximum power density of 11.23 W m-2 was obtained at 100 MΩ. Moreover, the device exhibits excellent energy-harvesting properties, including excellent stability and durability, rapidly charges capacitors, and lights commercial LEDs and digital tubes.

Low-Temperature Solution-Processed Cu2AgBiI6 Films for High Performance Photovoltaics and Photodetectors.

Recently, Cu2AgBiI6 semiconductor has been investigated due to the high absorption coefficient, direct bandgap, and low exciton binding energy, which are promising for eco-friendly photoelectric devices. Herein, pyridine is introduced as solvent additive to completely dissolve the solutes and form clear Cu2AgBiI6 precursor solution, which results in high-quality films and may provide a general approach for high-quality film growth of other bismuth-based metal halide semiconductors. In addition, the electronic structure of Cu2AgBiI6 has been demonstrated for the first time and shows an intrinsically weak n-type semiconductor. Furthermore, phenethylammonium iodide for surface passivation significantly improves the film quality, slightly n-dopes the material, and shifts up the band level. Finally, the photovoltaics and photodetector performance for n-i-p planar heterojunction devices have been investigated. The efficiency is up to 1%, highest for Cu2AgBiI6 solar cells and comparable with other lead-free bismuth based metal halide solar cells. Moreover, photodetectors with fast speed of rising and decaying time, especially the excellent specific photodetectivity of ∼1012 Jones within the wavelength of ∼350-600 nm, are achieved, which paves an alternative and promising strategy for the design of future commercial photodetectors that are self-powered, stable, nontoxic, etc.

Potential Applications of Halide Double Perovskite Cs2AgInX6 (X = Cl, Br) in Flexible Optoelectronics: Unusual Effects of Uniaxial Strains.

The discovery of halide double perovskite Cs2AgInX6 (X = Cl, Br) has provided an efficient way to search promising solar cell absorbers. Here, theoretical calculations on strained Cs2AgInX6 (X = Cl, Br) not only comprehensively and firstly help understand their physical properties but also provide a guideline to extend their potential applications. Although Cs2AgInX6 possesses a similar structure, the variations of physical properties of strained Cs2AgInX6 are different. Only compressive Cs2AgInBr6 undergoes a direct-to-indirect transition, which enables it to be a good radiation detection material. Moreover, the mobility of Cs2AgInCl6 is reduced by strains, while that of Cs2AgInBr6 is enhanced (reduced) by compression (tension). That is because the contribution degrees of Ag-d z2, d x2- y2 and In-d z2, d x2- y2 on the band edges of Cs2AgInX6 (X = Cl, Br) are inconsistent. In addition, the absorption coefficients of Cs2AgInX6 (X = Cl, Br) are deteriorated negligibly by strain, making it a potential material for further applications of photovoltaics and flexible optoelectronics.

Solution-Processed Air-Stable Copper Bismuth Iodide for Photovoltaics.

Bismuth-based solar cells have been under intensive interest as an efficient non-toxic absorber in photovoltaics. Within this new family of semiconductors, we herein report a new, long-term stable copper bismuth iodide (CuBiI4 ). A solutionprocessed method under air atmosphere is used to prepare the material. The adopted HI-assisted dimethylacetamide (DMA) co-solvent can completely dissolve CuI and BiI3 powders with high concentration compared with other organic solvents. Moreover, the high vapor pressure of tributyl phosphate, selected for the solvent vapor annealing (SVA), enables complete low-temperature (≤70 °C) film preparation, resulting in a stable, uniform, dense CuBiI4 film. The average grain size increases with the precursor concentration, greatly improving the photoluminescence lifetime and hall mobility; a carrier lifetime of 3.03 ns as well as an appreciable hall mobility of 110 cm2 V-1 s-1 were obtained. XRD illustrates that the crystal structure is cubic (space group Fd3m) and favored in the [1 1 1] direction. Moreover, the photovoltaic performance of CuBiI4 was also investigated. A wide bandgap (2.67 eV) solar cell with 0.82 % power conversion efficiency is presented, which exhibits excellent long-term stability over 1008 h under ambient conditions. This air-stable material may give an application in future tandem solar cells as a stable short-wavelength light absorber.

Dependence of Acetate-Based Antisolvents for High Humidity Fabrication of CH3NH3PbI3 Perovskite Devices in Ambient Atmosphere.

High-efficiency perovskite solar cells (PSCs) need to be fabricated in the nitrogen-filled glovebox by the atmosphere-controlled crystallization process. However, the use of the glovebox process is of great concern for mass level production of PSCs. In this work, notable efficient CH3NH3PbI3 solar cells can be obtained in high humidity ambient atmosphere (60-70% relative humidity) by using acetate as the antisolvent, in which dependence of methyl, ethyl, propyl, and butyl acetate on the crystal growth mechanism is discussed. It is explored that acetate screens the sensitive perovskite intermediate phases from water molecules during perovskite film formation and annealing. It is revealed that relatively high vapor pressure and high water solubility of methyl acetate (MA) leads to the formation of highly dense and pinhole free perovskite films guiding to the best power conversion efficiency (PCE) of 16.3% with a reduced hysteresis. The devices prepared using MA showed remarkable shelf life stability of more than 80% for 360 h in ambient air condition, when compared to the devices fabricated using other antisolvents with low vapor pressure and low water solubility. Moreover, the PCE was still kept at 15.6% even though 2 vol % deionized water was added in the MA for preparing the perovskite layer.

Morphology modulating the wettability of a diamond film.

Control of the wetting property of diamond surface has been a challenge because of its maximal hardness and good chemical inertness. In this work, the micro/nanoarray structures etched into diamond film surfaces by a maskless plasma method are shown to fix a surface's wettability characteristics, and this means that the change in morphology is able to modulate the wettability of a diamond film from weakly hydrophilic to either superhydrophilic or superhydrophobic. It can be seen that the etched diamond surface with a mushroom-shaped array is superhydrophobic following the Cassie mode, whereas the etched surface with nanocone arrays is superhydrophilic in accordance with the hemiwicking mechnism. In addition, the difference in cone densities of superhydrophilic nanocone surfaces has a significant effect on water spreading, which is mainly derived from different driving forces. This low-cost and convenient means of altering the wetting properties of diamond surfaces can be further applied to underlying wetting phenomena and expand the applications of diamond in various fields.

Wafer-scale double-layer stacked Au/Al2O3@Au nanosphere structure with tunable nanospacing for surface-enhanced Raman scattering.

Fabricating perfect plasmonic nanostructures has been a major challenge in surface enhanced Raman scattering (SERS) research. Here, a double-layer stacked Au/Al2O3@Au nanosphere structures is designed on the silicon wafer to bring high density, high intensity "hot spots" effect. A simply reproducible high-throughput approach is shown to fabricate feasibly this plasmonic nanostructures by rapid thermal annealing (RTA) and atomic layer deposition process (ALD). The double-layer stacked Au nanospheres construct a three-dimensional plasmonic nanostructure with tunable nanospacing and high-density nanojunctions between adjacent Au nanospheres by ultrathin Al2O3 isolation layer, producing highly strong plasmonic coupling so that the electromagnetic near-field is greatly enhanced to obtain a highly uniform increase of SERS with an enhancement factor (EF) of over 10(7). Both heterogeneous nanosphere group (Au/Al2O@Ag) and pyramid-shaped arrays structure substrate can help to increase the SERS signals further, with a EF of nearly 10(9). These wafer-scale, high density homo/hetero-metal-nanosphere arrays with tunable nanojunction between adjacent shell-isolated nanospheres have significant implications for ultrasensitive Raman detection, molecular electronics, and nanophotonics.