Perovskite solar cells have recently attracted significant attention as the promising candidate of commercial photovoltaic devices with high power conversion efficiency, low cost and large-scale processing. Anatase-type TiO2 is often used as an electronic transport layer in a state-of-the-art perovskite solar cells due to its excellent optical transmittance, semiconductor characteristics, and chemical stability. However, its rough surface with a large number of surface defects leads to poor crystallization of the perovskite film and serious hysteresis effect. Recent studies have shown that suitable interfacial modification plays an important role in enhancing power conversion efficiency and long-term stability of the perovskite solar cells. Several fused-ring electron acceptors have been introduced into n-i-p perovskite solar cells as the interfacial modifications for the electronic transport layer, which dramatically improve the performance and the long-term stability of the devices. The fused-ring electron acceptors are widely used as the electron acceptors in organic solar cells, and their structures are based on an electron donating fused ring with strong electron withdrawing groups, which contributes to adjustable optical band gap and energy level structure, good electronic transfer capability, excellent thermal and photochemical stability. Therefore, a facile interface engineering method for all-solution-processed perovskite solar cells is reported in this paper. The fused-ring electron acceptor ITIC-Th containing alkylthiophene side chains is applied to modify TiO2 electronic transport layer to prepare the planar perovskite solar cells with excellent performance and stability. The main results and discussions are summarized as follows: (1) The ITIC-Th modified TiO2 film is much denser and smoother than the original TiO2 film. The images of scanning electron microscope show that the interfacial modification using ITIC-Th improves the morphology and increases the water contact angle of the electronic transport layer, which effectively enhances the quality and grain size of the perovskite crystals. (2) The characterizations of the electronic transport layer by UV-Vis transmission and photoluminescence spectroscopy indicate that ITIC-Th produces additional light absorption in the wavelength interval from 550 to 750 nm, so the transmittance of the modified electronic transport layer is slightly lower than that of ITO/TiO2 substrate; however, ITIC-Th has a strong fluorescence quenching effect, resulting in beneficial properties on the extraction, transportation and collection of photogenerated carriers for the modified electronic transport layer, which greatly reduces the surface recombination of charge carriers. (3) Planar solar cells with the structure of ITO/electronic transport layer/(FAPbI(3))(x)(MAPbCl(3))(1-x)/spiro-OMeTAD/Ag are successfully prepared. Consequently, the champion power conversion efficiency of the perovskite solar cells increases from 15.43% to 18.91% after the introduction of ITIC-Th. Moreover, the stability of the perovskite solar cells without encapsulation is investigated. As a result, the TiO2/ITIC-Th based device exhibits excellent stability with only 10% degradation after 1000 h in ambient humidity of 30% at room temperature, which is superior to that of the TiO2 based device. This work provides an important candidate in practical application for improving the performance of perovskite solar cells.

In this work, we report a novel kind of Si3N4/SiC composite fibers, which exhibit a controlled gradient Si3N4(shell)/SiC(core) structure. These composite fibers are fabricated through a controlled nitridation and pyrolysis process on electron irradiation-cured polycarbosilane fibers. Structural and chemical analysis based on Elemental Analyzer, FT-IR, Raman spectroscopy, electron probe micro-analyzer, X-ray photoelectron spectroscopy, and X-ray diffraction confirm the gradient structure of obtained fibers, which consist a shell with high Si3N4 content and a SiC core. The as-fabricated fibers exhibit dense and smooth surfaces, and no microscopic holes or defects were observed. The effects of nitridation temperature on mechanical properties and electrical resistivity were also investigated. Combined with high mechanical properties and lightweight, the present gradient Si3N4/SiC fibers open a new strategy to fabricate multifunctional and electromagnetic wave absorbing materials.

Different mass fraction of iron-containing silicon carbide(Fe/SiC)ceramics was successfully prepared by firstly synthesizing iron(Fe)-containing precursor via blending Fe colloids formed by the reaction of liquid polycarbosilane(PCS)and carbonyl iron with solid PCS and then the cross-linking and pyrolysis.The effects of the introduction of Fe on the component, structure, and magnetic and dielectric properties were systematically studied.When the mass fraction of iron is less than 8.94%, Fe element can significantly promote the decomposition of SiC xOyand generate β-SiC,and the crystallization peak of β-SiC is sharper with increased Fe.But when the Fe mass fraction increases to 11.78%, the main product is Fe3Si; Fe-SiC ceramics are all ferromagnetic,and their saturation magnetization increases exponentially with the increase of iron.Fe/SiC ceramic with 4.19%Fe has a minimum -9.4 dB reflection loss at 12.4 GHz.The bandwidths of less than -5 dB for Fe/SiC cermic with 4.19%and 8.94% Fe are 2.4 GHz and 3.7 GHz,respectively, which can be used as good microwave-absorption materials.

SiNO ceramic has very excellent comprehensive properties and is one of the best candidates for ceramic matrix composites.In this work,influences of pyrolysis and curing conditions on the SiNO ceramic prepared with pyrolysis nitridation are systematically studied.The results show that decarbonization is completed before 800 ℃ with carbon residue lower than 1%(by mass).After pyrolysis in N2,nitrogen content is as high as 35.65%(by mass).Oxidation curing before ammonolysis can improve ceramic yield.The ceramic yield is 61.84%(by mass)but the nitrogen content decreases significantly(below 20%)by mass,and the product is amorphous SiNO ceramic.Therefore,high-yield and low-carbon-content SiNO ceramic can be prepared with pyrolysis nitridation of polycarbosilane.