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The high-temperature stability of the SiC ultrafine fibers is limited by the massive amounts of oxygen introduced during the oxidative curing process. In this study, vinyl-modified polycarbosilane (Vi-PCS) was synthesized through the hydrosilylation reaction of PCS and divinyldimethylsilane at 320 °C. The electrospun ultrafine Vi-PCS fibers were cured by heating to 320 °C in an inert atmosphere, initiating a subsequent hydrosilylation reaction. Subsequent pyrolysis at 1200 °C yielded SiC ultrafine fibers with uniform diameters (1.6–2.5 μm) and low oxygen content (4.64 wt%). The fibers retained their smooth surface morphology and flexibility up to 1700 °C due to the significant reduction of the SiC x O y phase. The resulting SiC ultrafine fibrous mats are promising materials for applications in harsh environments because of their high-temperature stability and low preparation cost. [ABSTRACT FROM AUTHOR]

Precursor impregnation and pyrolysis (PIP) is an important process to fabricate fiber-reinforced SiC matrix composites, and a low viscous, curable, long-storable, and affordable liquid precursor is urgently needed. To meet the above requirements, a liquid two-component precursor system is proposed, which contains (1) the liquid by-product of polycarbosilane (b-PCS), and (2) organosilicon compound with double carbon bond. The b-PCS with the M ‾ w value of 635 is mainly composed of the oligomers of carbosilane with abundant amount of Si–H active groups. Four candidates of organosilicon compounds including tetramethyldivinyldisilazane (TMDS), methyltriallysilane (MTAS), Tetraallylsilane(TAS), and 1,3,5-Trivinyl-1,3,5-trimethylcyclotrisilazane (TVSN) were used, called crosslinkers. The effect of different crosslinkers on curing and pyrolysis process was investigated via TG-DSC, FTIR and TG-FTIR-MS, et al. Based on the results of the total ceramic yield, TVSN is the optimized crosslinker of four candidate organosilicon compounds. The ceramic product of corresponding two-component precursor was also characterized via element analysis, compositional element Si, C, N, and O account for 54.77 wt%, 36.23 wt%, 6.83 wt%, 2.07 wt%, respectively. Moreover, the two-component precursor has excellent storage stability at room temperature. [ABSTRACT FROM AUTHOR]

In recent years, the primary reasons for low efficiency Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells have been attributed to Sn Zn defects and related defect clusters, as well as the balance of absorption layer bandgap for short-circuit current density (J sc) and open-circuit voltage (V oc). Ge gradient has been theoretically proven to be an effective strategy to change traditional flat bandgap structure and suppress Sn Zn defects and related defect clusters for improving the device performance of CZTSSe solar cells. However, the potential of Ge gradient has not been fully verified. In this work, Ge doping effectively reduces the formation of Sn Zn defects and [2Cu Zn + Sn Zn ] defect clusters in the CZTSSe absorption layer. In addition, it can be found that the construction of the V-type bandgap is the best solution for balancing between V oc and J sc. By using the bandgap grading strategy, the disparity between the recombination barrier of the junction and the optical bandgap's minimum value is widened, thereby obtaining a large V oc. The V-type doped device has the highest efficiency when V oc is 0.45 V, which can reach 8.03%. This Ge graded substitution method provides an alternative absorption layer structure for improving V oc and the preparation of future high-efficiency kesterite photovoltaic devices. [ABSTRACT FROM AUTHOR]

Improving the performance of thermoelectric (TE) materials and fabricating TE devices with higher conversion efficiency remains a significant challenge in materials research. The low figure of merit (ZT) value of n -type bismuth telluride has seriously hindered the development of TE devices based on bismuth telluride. Element doping and nanostructured defect introduction have commonly been employed to improve TE properties. Herein, we utilized high-pressure synthesis to fabricate n -type Bi 2 Se 0.3 Te 2.7 bulk nanomaterials and enhance their TE performance by adjusting the fabrication pressure and titanium doping concentration. Through this process, titanium effectively substituted bismuth to decrease carrier concentration and improve carrier mobility. As a result, the thermal conductivity was significantly decreased. By employing a fabrication pressure of 2.5 GPa and 10 at % Ti doping, a remarkable ZT value of 0.96 was achieved at 333 K, which was 2.8 times the undoped counterparts. These findings demonstrate a successful design methodology and fabrication process to generate n -type Bi 2 Te 3 with outstanding TE performance. This study provided valuable insights into the synthesis of high-performance TE materials and contributed to advancements in TE device technology. [ABSTRACT FROM AUTHOR]

Crystallization growth occupies a crucially important role in terms of impacting the film microstructure and device characteristics of the kesterite Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cell. Previous studies frequently observed that the selenized CZTSSe film consists of a multiple-layer structure with a large-grained top layer and a fine-grained bottom layer. Herein, a novel strategy is proposed for adjusting spin-coated layers and conducting two-step selenization to promote the fine-grain layers growth of Bi-doped CZTSSe (CZTBiSSe) films for high-performance solar cells. This study systematically investigates the effects of spin-coated layers and the selenization process on growth kinetics of the CZTBiSSe films. By comparison, the optimal spin-coated layer can be identified as "7 + 3", the CZTBiSSe film has a bilayer large grain structure from up to down, which reduces the grain boundaries, thus reducing the charge recombination loss, and is more conducive to charge carrier transfer. Finally, a CZTBiSSe solar cell with the highest efficiency of 7.27 % was obtained, which increased by 36 % more than one prepared using traditional methods (5.34 %). [ABSTRACT FROM AUTHOR]

Bismuth telluride is a widely used commercial thermoelectric material with excellent thermoelectric performances near room temperature. Reducing thermal conductivity is one of the most effective ways to improve performances of thermoelectric materials. In this study, the thermal conductivity of the material was reduced by fabricating porous structures. Highly dense NaCl-(Bi,Sb) 2 Te 3 composites were fabricated by a high-pressure technology. The NaCl phase was then removed from the composites by ultrasonic washing to produce porous structures. The produced (Bi,Sb) 2 Te 3 porous materials possessed excellent thermoelectric properties. The porosity and pore size of the (Bi,Sb) 2 Te 3 porous materials increased with the increasing NaCl content, decreasing the thermal conductivity significantly. An ultra-low lattice thermal conductivity of 0.21 Wm−1K−1 at 493 K was achieved when the porosity was 39%, almost the lowest lattice thermal conductivity reported for (Bi,Sb) 2 Te 3 bulk materials. The figure of merit ZT value was enhanced to 1.05 at 493 K when the porosity was 25%. Compared with the most compacted samples (ZT = 0.79 and porosity of 10%) prepared under the same conditions, the ZT value of the porous samples increased by 33%. This study indicated that porous thermoelectric materials can be prepared simply, quickly and efficiently by high-pressure/ultrasonication washing to improve thermoelectric performances, which has evident reference values for preparing other thermoelectric pore materials with enhancing behaviors. [ABSTRACT FROM AUTHOR]

We report the ferromagnetic enhancement in a rare-earth and nitrogen co-doped ZnO thin film. To reveal the origin of ferromagnetism, we perform a comparative study on undoped, Nd-doped, N-doped and (Nd, N)-codoped ZnO thin films by combining experiments with first-principles calculations. Compared with the Nd-doped ZnO, the N incorporation into the Nd-doped ZnO to form 2Nd Zn -N O complex leads to the more stable ferromagnetic coupling between two Nd atoms, which is well supported by first-principles calculations. Our results suggest that the electronic structure alteration via codoping engineering plays a critical role in stabilizing the ferromagnetic orderings. [ABSTRACT FROM AUTHOR]

We fabricated high-quality n-type Ag 2 ZnSnSe 4 (AZTSe) film with kesterite structure by using a simple solution method. A Cu 2 ZnSnSe 4 (CZTSe)/AZTSe-based solar cell was designed and prepared by inserting AZTSe layer between CZTSe and CdS of the traditional CZTSe-based solar cell. Compared with the traditional device, an increase from 337 to 432 mV in open circuit voltage (V oc) and an accompanying rise from 3.40% to 4.72% in power conversion efficiency (PCE) were observed. To well understand the PCE improvement of the CZTSe/AZTSe-based solar cells, we calculated the band alignments of CZTSe/AZTSe and CZTSe/CdS heterojunctions using first-principles calculations, demonstrating that the CZTSe/AZTSe and CZTSe/CdS interfaces have type-II and type-I band alignments, respectively. Moreover, the band offset of AZTSe/CdS is lager than the one of CZTSe/CdS. Combined with the calculation results, the mechanism of influence of the AZTSe on the PCE improvement is discussed in detail. Our conclusions show that the addition of the AZTSe layer is a potentially applicable method to obtain CZTSe-based solar cells with higher V oc and PCE. [Display omitted] [ABSTRACT FROM AUTHOR]

Element doping into the Cu 2 ZnSn(S,Se) 4 (CZTSSe) absorber is an effective method to optimize the performance of thin film solar cells. In this study, the Cu 2 In x Zn 1-x Sn(S,Se) 4 (CIZTSSe) precursor film was deposited by magnetron cosputtering technique using indium (In) and quaternary Cu 2 ZnSnS 4 (CZTS) as targets. Meanwhile, the In content was controlled using the direct current (DC) power on In target (P In). A single kesterite CIZTSSe alloy was formed by successfully doping a small number of In3+ into the main lattice of CZTSSe. The partial Zn2+ cations were substituted by In3+ ions, resulting in improving properties of CZTSSe films. Morphological analysis showed that large grain CIZTSSe films could be obtained by doping In. The well-distributed, smooth, and dense film was obtained when the P In was 30 W. The band gap of CIZTSSe could be continuously adjusted from 1.27 to 1.05 eV as P In increased from 0 to 40 W. In addition, the CIZTSSe alloy thin film at P In = 30 W exhibited the best p-type conductivity with Hall mobility of 6.87 cm2V−1s−1, which is a potential material as the absorption layer of high-performance solar cells. [ABSTRACT FROM AUTHOR]

(Na 0.1 Cu 0.9) 2 ZnSn(S,Se) 4 thin films with a single kesterite phase were synthesized using a sol-gel spin-coating method accompanied by rapid post-annealing. In this study, we investigated the effect of selenization time on the crystal quality and photoelectric performance of the (Na 0.1 Cu 0.9) 2 ZnSn(S,Se) 4 films. It was found that the crystallinity and morphology of the films was enhanced, and some of bigger Se substituted for the S site in (Na 0.1 Cu 0.9) 2 ZnSn(S,Se) 4 with increasing the selenization time. The bandgap of the film can be regulated from 1.04 eV to 0.99 eV by varying the selenization time. In addition, all films showed p-type conductive characteristics, and films with optimal electrical performance could be obtained by optimizing the selenization time. Finally, the (Na 0.1 Cu 0.9) 2 ZnSn(S,Se) 4 thin film with the best crystal quality and optical-electrical characteristics was obtained at an optimized selenization time of 15 min. A high power conversion efficiency (PCE) of 3.92% was obtained for the (Na 0.1 Cu 0.9) 2 ZnSn(S,Se) 4 device, which is 42% higher compared to that of the undoped Cu 2 ZnSn(S,Se) 4 (CZTSSe) device. [ABSTRACT FROM AUTHOR]

Highly dense Al 2 O 3 Y 3 Al 5 O 12 (YAG) eutectic bulk ceramics are successfully prepared by spark plasma sintering (SPS) using fine ceramic particles with homogeneous eutectic structure. The fine ceramic particles are obtained by pulverizing the eutectic ceramic rods prepared with laser floating zone melting (LFZM). The densification and microstructural evolution of eutectic ceramic particles during SPS are investigated. The results show that the sintering process can be divided into four stages, and densification is mainly accomplished with a short time in the stage of 1450–1580 °C. High-temperature diffusions on grain surface and in lattice or grain boundary of fine particles are primary densification mechanisms. Three types of microstructural evolutions during sintering are revealed, in which large eutectic particles mainly consolidate with an indirect way due to fine particles between them. On the basis, the effects of sintering temperature on microstructure and mechanical properties are discussed. The results pave a feasible way to prepare bulk eutectic ceramics with enhanced toughness by sintering method. [ABSTRACT FROM AUTHOR]

Abstract We report an ultraviolet (UV) electroluminescence (EL) in n-SnO 2 /p-ZnO heterojunction light-emitting diodes with the nanostructural SnO 2 as an n-type layer and the Li-doped ZnO (ZnO:Li) synthesized by high-temperature high-pressure (HTHP) method as a high hole concentration p-type layer. Two kinds of SnO 2 nanostructures including nanobelts (NBs) and nanowires (NWs) were used to fabricate n-type layers in the heterojunctions. The two heterojunctions with different SnO 2 nanostructures demonstrate different light-emission feature in EL measurements. The SnO 2 NBs/p-ZnO heterojunction shows a blue emission band centered at 416 nm under forward-bias voltage. A strong UV emission peak located at 391 nm was observed for the SnO 2 NWs/p-ZnO heterojunction. Photoluminescence (PL) spectra indicate that the difference in EL is attributed to morphology-dependent light-emission feature in nanostructural SnO 2 layer. Our results suggest that the nanostructural SnO 2 /ZnO:Li heterojunction is a potential and promising system in the UV optoelectronic field. [ABSTRACT FROM AUTHOR]

We have synthesized Cu 2 Mg x Zn 1–x Sn(S,Se) 4 (0 ≤ x ≤ 0.6) thin films by a facile sol-gel method, and studied the influence of Mg concentration on the crystal structure, surface morphology and photoelectric performance of Cu 2 Mg x Zn 1–x Sn(S,Se) 4 thin films systematically. It was shown that the smaller Zn 2+ in Kesterite phase Cu 2 ZnSn(S,Se) 4 will be replaced by larger Mg 2+ , forming uniform pure phase Cu 2 Mg x Zn 1–x Sn(S,Se) 4 . The band gap of Cu 2 Mg x Zn 1–x Sn(S,Se) 4 films can be adjusted from 1.12 to 0.88 eV as the x value changes from 0 to 0.6. Furthermore, the Cu 2 Mg x Zn 1–x Sn(S,Se) 4 thin films with large grain size, smooth surface and less grain boundaries was obtained at an optimized condition of x = 0.2. The carrier concentration of Cu 2 Mg x Zn 1–x Sn(S,Se) 4 thin film reaches the maximum 6.47 × 10 18 cm −3 at x = 0.2, which is a potential material to be the absorption layer of high efficiency solar cells. [ABSTRACT FROM AUTHOR]

Bandgap engineering of Cu 2 In x Zn 1−x Sn(S,Se) 4 alloy films for photovoltaic application has been investigated. Cu 2 In x Zn 1−x Sn(S,Se) 4 (0 ≤ x ≤ 0.6) alloy films with different In contents and a single kieserite phase were fabricated by using a simple low-cost sol-gel method. The influence of In content on the structure, morphology, and optical and electrical properties of Cu 2 In x Zn 1−x Sn(S,Se) 4 films was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscope (TEM), X-Ray photoelectron spectroscopy (XPS), optical absorbance, and room-temperature Hall measurements. The results of XRD, TEM, and XPS demonstrated the substitution of some Zn atoms by In in Cu 2 In x Zn 1−x Sn(S,Se) 4 films. The Hall measurements show that the carrier concentration of the Cu 2 In x Zn 1−x Sn(S,Se) 4 (0 ≤ x ≤ 0.6) decreases with increasing In content and that the p-type Cu 2 In x Zn 1−x Sn(S,Se) 4 films with preferable electrical properties can be obtained by adjusting the In content during film deposition. The optical measurements indicate that the bandgap of Cu 2 In x Zn 1−x Sn(S,Se) 4 films with kesterite structure can be continuously tuned in the range of 1.13–1.01 eV as x is increased from 0 to 0.6. Our results show that the Cu 2 In x Zn 1−x Sn(S,Se) 4 alloy is a potentially applicable material for bandgap grading absorption layers in high-power-conversion-efficiency solar cells. [ABSTRACT FROM AUTHOR]

We reported a highly spectrum-selective ultraviolet photodiode based on In 2 O 3 with dipole-forbidden bandgap transition. The near-band-edge ultraviolet emission and absorption were observed in the hybrid In 2 O 3 films with the In 2 O 3 nanocrystals embedded into the amorphous In 2 O 3 matrix, indicating that the dipole-forbidden rule of bulk In 2 O 3 is broken. The hybrid In 2 O 3 film was deposited on the p-GaN/sapphire wafer to form an In 2 O 3 /p-GaN heterojunction photodiode. The photodiode showed an obvious rectifying behavior in a current–voltage measurement and a narrow-band ultraviolet photoresponse at the near-band-edge region under back-illumination conditions. Electronic structure calculations based on the first-principles method demonstrate that the breaking of dipole-forbidden transition rule is derived from the surface states of In 2 O 3 nanocrystals. Our results suggest that tailoring the In 2 O 3 nanocrystalline structure is an effective route to achieving novel optical properties and applying these properties to the ultraviolet optoelectronic field. [ABSTRACT FROM AUTHOR]

Transparent Mg-doped p-type conductive SnO 2 thin films were fabricated on quartz substrates by sol–gel method. Effect of Mg doping on structural, morphological, optical, and electrical properties of SnO 2 films were investigated. A single phase of tetragonal rutile structure was observed in Mg-doped SnO 2 films. The optical bandgap energy of the Mg-doped SnO 2 films showed a systematical redshift with respect to the undoped SnO 2 film, and the resistivity significantly increased with the increase of Mg concentration. A conduction type transform from n to p was also observed. The strong ultraviolet and comparatively weak blue/green emissions were observed in room temperature photoluminescence, suggesting the dipole-forbidden rule of bulk SnO 2 is broken in Mg-doped SnO 2 films. These results were supported by first-principles electronic structure calculations. [ABSTRACT FROM AUTHOR]