The effects of Ag on the microstructure and corrosion behavior of pre-soldering Sn-xAg lead-free solders,and on the formation of intermetallic layer of the solders with Cu substrate were investigated.The Ag contents(x...The effects of Ag on the microstructure and corrosion behavior of pre-soldering Sn-xAg lead-free solders,and on the formation of intermetallic layer of the solders with Cu substrate were investigated.The Ag contents(x)were 0,3.0,3.5,4.0,and5.0 wt.%.The Ag content played a role in the morphology of Ag3 Sn phase in the solders.The microstructure analysis showed that theβ-Sn phase was surrounded by eutectic networks in the 3.0 Ag and 3.5 Ag solders and large plate-like Ag3 Sn formed in the 4.0 Ag and5.0 Ag solders.Nonetheless,the Ag content slightly impacted the corrosion behavior of the as-cast solders as characterized using potentiodynamic polarization test.After soldering,only a single layer of a Cu6 Sn5 intermetallic compound formed at the Sn-xAg/Cu interface.By comparison,the Cu6 Sn5 intermetallic layer of the Ag-doped solders was thinner than that of the 0Ag solder.The fine Ag3 Sn particles in the eutectic networks precipitating in the 3.0 Ag and 3.5 Ag solders effectively hindered the growth of Cu6 Sn5 grains compared to large plate-like Ag3 Sn in the 4.0 and 5.0Ag solders.展开更多
A multi-grain phase field model coupled with thermodynamic calculation was adopted to describe the dendritic growth in pressurized solidification of Mg-A1 alloy during squeeze casting, in which the effects of the pres...A multi-grain phase field model coupled with thermodynamic calculation was adopted to describe the dendritic growth in pressurized solidification of Mg-A1 alloy during squeeze casting, in which the effects of the pressure on the Gibbs free energy and chemical potential of solid and liquid phases, the solute diffusion coefficient, and the solute partition coefficient were considered. The individual effect of solute diffusion coefficient, and the Gibbs free energy on the dendritic growth was studied. With the compar- ison of the dendritic growth under atmospheric and elevated pressures, the effect of pressure on the microstructure evolution was discussed. The results showed that the grains are refined, the dendritic growth rate tends to increase and the secondary dendrite arms are more developed as the pressure is increased from 0.1 to 100 MPa, which showed a good agreement with the experimental results of direct squeeze casting of Mg-AI alloy. As the pressure increases, the largest dendritic growth rate can be obtained under the pressure between 200 and 250 MPa, while the growth rate decreases with a further increase of pressure.展开更多
Phase transition and phase separation of formamidinium-cesium(FA-Cs)perovskite during the fabrication and operation processes reduce the efficiency and stability of perovskite solar cells(PSCs).Here,we develop an in s...Phase transition and phase separation of formamidinium-cesium(FA-Cs)perovskite during the fabrication and operation processes reduce the efficiency and stability of perovskite solar cells(PSCs).Here,we develop an in situ molecular self-assembly approach on perovskite surface using an amine nickel porphyrin(NiP).The NiP doped perovskite precursor solution was deposited on substrate by blade-coating under ambient condition.NiP molecules self-assemble into supramolecule bound on perovskite surface during the vacuum-assisted process.Such a modification controls the perovskite grain growth to generate the uniform perovskite film.The supramolecule can release the residual lattice strain to inhibit the phase transition of perovskite film,and promote the charge extraction and transport to suppress the phase separation of FA-Cs perovskite during long-term illumination condition.Consequently,the best efficiency of large-area NiP-based FA-Cs-PSCs with the active area of 1.0 cm2 is up to 20.3%(certified as 19.2%),which is close to the record efficiency(20.37%)by blade-coating.Unencapsulated NiP-doped device reveals the remarkably improved overall stabilities.This work affords a novel way to address the phase transition and phase separation in FA-Cs perovskite.展开更多
Molecular dielectric switches constitute a type of intelligent materials that are highly coveted for their distinctive advantages of switchable dielectric responses,lightweight,and mechanical flexibility.Twodimensiona...Molecular dielectric switches constitute a type of intelligent materials that are highly coveted for their distinctive advantages of switchable dielectric responses,lightweight,and mechanical flexibility.Twodimensional(2D)hybrid perovskites have demonstrated excellent promise for assembling dielectric switches,in which the dynamic motions of organic moieties afford driving force to trigger switchable dielectric phase transition.Here,we successfully assembled a new lead-free hybrid double perovskite,(CHA)4Cu Bi Br8(1,CHA=cyclohexylammonium),adopting a typical 2D structural motif,which shows dielectric anisotropy and bistable behaviors during the reversible phase transition near T_(c)=378 K(the Curie temperature).That is,its dielectric constants could be switched and tuned between high-dielectric and low-dielectric states.Structure analyses reveal that the ordered-disordered transformation of the organic CHA+moiety and distortion of inorganic framework account for its phase transition.This result will stimulate further exploration of molecular dielectric switches in this 2D environmentally friendly family.展开更多
CsPbBr_(3)inorganic perovskites have been regarded as the promising materials in the field of photo-voltaics because of the high tolerance against environment.The high energy barrier of phase transition from lead brom...CsPbBr_(3)inorganic perovskites have been regarded as the promising materials in the field of photo-voltaics because of the high tolerance against environment.The high energy barrier of phase transition from lead bromide(PbBr_(2))to CsPbBr_(3)perovskite and low solubility of perovskite in organic solvent impede the further improvement of device performance in terms of CsPbBr_(3)solar cells.Herein,an intermediate phase-assisted growth of CsPbBr_(3)perovskite was proposed by introducing tetraphenylphosphonium bromide(TPPB)as additive.The TPPB is expected to react with PbBr_(2)in organic solvent to form an intermediate phase of[TPPB.DMF]-PbBr_(2),which not only effectively improves the crystallinity of PbBr2 crystals,but also greatly reduces the phase transition energy barrier,leading to uniform and compact CsPbBr_(3)perovskite films with large grain size and high crystallinity.In combination with carbon electrode,the CsPbBr_(3)solar cells yield a champion device performance of 9.57%in comparison of pristine CsPbBr_(3)solar cells showing a low efficiency of 8.17%.Furthermore,the intermediate phaseassisted growth of CsPbBr_(3)-based solar cells displays an outstanding storage over720 h.展开更多
文摘The effects of Ag on the microstructure and corrosion behavior of pre-soldering Sn-xAg lead-free solders,and on the formation of intermetallic layer of the solders with Cu substrate were investigated.The Ag contents(x)were 0,3.0,3.5,4.0,and5.0 wt.%.The Ag content played a role in the morphology of Ag3 Sn phase in the solders.The microstructure analysis showed that theβ-Sn phase was surrounded by eutectic networks in the 3.0 Ag and 3.5 Ag solders and large plate-like Ag3 Sn formed in the 4.0 Ag and5.0 Ag solders.Nonetheless,the Ag content slightly impacted the corrosion behavior of the as-cast solders as characterized using potentiodynamic polarization test.After soldering,only a single layer of a Cu6 Sn5 intermetallic compound formed at the Sn-xAg/Cu interface.By comparison,the Cu6 Sn5 intermetallic layer of the Ag-doped solders was thinner than that of the 0Ag solder.The fine Ag3 Sn particles in the eutectic networks precipitating in the 3.0 Ag and 3.5 Ag solders effectively hindered the growth of Cu6 Sn5 grains compared to large plate-like Ag3 Sn in the 4.0 and 5.0Ag solders.
基金funded by the National Natural Science Foundation of China (Grant No.51175291)Tsinghua University Initiative Scientific Research Program(Grant No.2011Z02160)the State Key Laboratory of Automotive Safety and Energy,Tsinghua University under the contract 2013XC-A-01
文摘A multi-grain phase field model coupled with thermodynamic calculation was adopted to describe the dendritic growth in pressurized solidification of Mg-A1 alloy during squeeze casting, in which the effects of the pressure on the Gibbs free energy and chemical potential of solid and liquid phases, the solute diffusion coefficient, and the solute partition coefficient were considered. The individual effect of solute diffusion coefficient, and the Gibbs free energy on the dendritic growth was studied. With the compar- ison of the dendritic growth under atmospheric and elevated pressures, the effect of pressure on the microstructure evolution was discussed. The results showed that the grains are refined, the dendritic growth rate tends to increase and the secondary dendrite arms are more developed as the pressure is increased from 0.1 to 100 MPa, which showed a good agreement with the experimental results of direct squeeze casting of Mg-AI alloy. As the pressure increases, the largest dendritic growth rate can be obtained under the pressure between 200 and 250 MPa, while the growth rate decreases with a further increase of pressure.
基金We acknowledge the National Natural Science Foundation of China(No.22075116)Fundamental Research Funds for the Central Universities of China(No.lzujbky-2021-ey10)Science and Technology program of Gansu Province(No.20JR5RA305).
文摘Phase transition and phase separation of formamidinium-cesium(FA-Cs)perovskite during the fabrication and operation processes reduce the efficiency and stability of perovskite solar cells(PSCs).Here,we develop an in situ molecular self-assembly approach on perovskite surface using an amine nickel porphyrin(NiP).The NiP doped perovskite precursor solution was deposited on substrate by blade-coating under ambient condition.NiP molecules self-assemble into supramolecule bound on perovskite surface during the vacuum-assisted process.Such a modification controls the perovskite grain growth to generate the uniform perovskite film.The supramolecule can release the residual lattice strain to inhibit the phase transition of perovskite film,and promote the charge extraction and transport to suppress the phase separation of FA-Cs perovskite during long-term illumination condition.Consequently,the best efficiency of large-area NiP-based FA-Cs-PSCs with the active area of 1.0 cm2 is up to 20.3%(certified as 19.2%),which is close to the record efficiency(20.37%)by blade-coating.Unencapsulated NiP-doped device reveals the remarkably improved overall stabilities.This work affords a novel way to address the phase transition and phase separation in FA-Cs perovskite.
基金financially supported by National Natural Science Foundation of China(Nos.22125110,22205233,22193042,21833010,21921001,and U21A2069)the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(No.ZDBSLY-SLH024)+3 种基金the National Postdoctoral Program for Innovative Talents(No.BX2021315)the National Key Research and Development Program of China(No.2019YFA0210402)the China Postdoctoral Science Fund(No.2022TQ0337)Fujian Science&Technology Innovation Laboratory for Optoelectronic Information of China(No.2021ZR126)。
文摘Molecular dielectric switches constitute a type of intelligent materials that are highly coveted for their distinctive advantages of switchable dielectric responses,lightweight,and mechanical flexibility.Twodimensional(2D)hybrid perovskites have demonstrated excellent promise for assembling dielectric switches,in which the dynamic motions of organic moieties afford driving force to trigger switchable dielectric phase transition.Here,we successfully assembled a new lead-free hybrid double perovskite,(CHA)4Cu Bi Br8(1,CHA=cyclohexylammonium),adopting a typical 2D structural motif,which shows dielectric anisotropy and bistable behaviors during the reversible phase transition near T_(c)=378 K(the Curie temperature).That is,its dielectric constants could be switched and tuned between high-dielectric and low-dielectric states.Structure analyses reveal that the ordered-disordered transformation of the organic CHA+moiety and distortion of inorganic framework account for its phase transition.This result will stimulate further exploration of molecular dielectric switches in this 2D environmentally friendly family.
基金financially supported by the National Natural Science Foundation of China(No.U1632151)the Natural Science Foundation of Anhui Province,China(Nos.2108085ME149 and 2308085QE137)+2 种基金the State Key Laboratory of Pulsed Power Laser Technology,China(No.SKL2021ZR03)Anhui innovation and entrepreneurship support plan for Returned Overseas Students(No.2022LCX018)the Key Research and Development Plan of Anhui Province(No.212023t07020005)。
文摘CsPbBr_(3)inorganic perovskites have been regarded as the promising materials in the field of photo-voltaics because of the high tolerance against environment.The high energy barrier of phase transition from lead bromide(PbBr_(2))to CsPbBr_(3)perovskite and low solubility of perovskite in organic solvent impede the further improvement of device performance in terms of CsPbBr_(3)solar cells.Herein,an intermediate phase-assisted growth of CsPbBr_(3)perovskite was proposed by introducing tetraphenylphosphonium bromide(TPPB)as additive.The TPPB is expected to react with PbBr_(2)in organic solvent to form an intermediate phase of[TPPB.DMF]-PbBr_(2),which not only effectively improves the crystallinity of PbBr2 crystals,but also greatly reduces the phase transition energy barrier,leading to uniform and compact CsPbBr_(3)perovskite films with large grain size and high crystallinity.In combination with carbon electrode,the CsPbBr_(3)solar cells yield a champion device performance of 9.57%in comparison of pristine CsPbBr_(3)solar cells showing a low efficiency of 8.17%.Furthermore,the intermediate phaseassisted growth of CsPbBr_(3)-based solar cells displays an outstanding storage over720 h.
