The characteristics of turbulent boundary layer over streamwise aligned drag reducing riblet surface under zero-pressure gradient are investigated using particle image velocimetry. The formation and distribution of la...The characteristics of turbulent boundary layer over streamwise aligned drag reducing riblet surface under zero-pressure gradient are investigated using particle image velocimetry. The formation and distribution of large-scale coherent structures and their effect on momentum partition are analyzed using two-point correlation and probability density function. Compared with smooth surface, the streamwise riblets reduce the friction velocity and Reynolds stress in the turbulent boundary layer, indicating the drag reduction effect. Strong correlation has been found between the occurrence of hairpin vortices and the momentum distribution. The number and streamwise length scale of hairpin vortices decrease over streamwise riblet surface. The correlation between number of uniform momentum zones and Reynolds number remains the same as smooth surface.展开更多
Metal halide perovskite solar cells(PSCs)are anticipated to play a pivotal role in the next generation of photovoltaic technologies,but their unsatisfactory stability hinders further commercial applications.Particular...Metal halide perovskite solar cells(PSCs)are anticipated to play a pivotal role in the next generation of photovoltaic technologies,but their unsatisfactory stability hinders further commercial applications.Particularly,numerous interfacial defects and poor mechanical adhesion at the perovskite buried interface present a critical obstacle hindering power conversion efficiency(PCE)and longterm stability of PSCs.Here,different from conventional small-molecule or linear polymer interface modifiers,we introduce a star-shaped PMMA-b-PDMAEMA(S-MD,where PMMA=poly(methyl methacrylate)and PDMAEMA=poly(dimethylaminoethyl methacrylate))polymer as a multifunctional bridge-linking polymer for simultaneous defect passivation and mechanical reinforcement at the buried interface of inverted(p-i-n)PSCs.S-MD features a three-dimensional architecture with multiple extended conjugated arms,offering multiple Lewis base functional groups(e.g.,C=O and R-N(CH_(3))_(2))with a high density of multidentate coordination sites.These groups can effectively coordinate with electron-deficient defects at the perovskite buried interface,enabling improved crystallization,reduced defect density,and enhanced interfacial adhesion.As a result,the interfacial fracture strength increases from 0.13 to 1.66 MPa.The resultant device achieves a PCE of 26.35%(certified steady-state PCE of 25.96%).The flexible device retains over 90%of its initial efficiency after 3000 flexing cycles at a curvature radius of 6 mm(R=6 mm).This work highlights a multidentate coordinating,star-shaped polymer interface strategy that offers a promising pathway toward highly efficient and stable inverted PSCs.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 11721202 and 11672020)
文摘The characteristics of turbulent boundary layer over streamwise aligned drag reducing riblet surface under zero-pressure gradient are investigated using particle image velocimetry. The formation and distribution of large-scale coherent structures and their effect on momentum partition are analyzed using two-point correlation and probability density function. Compared with smooth surface, the streamwise riblets reduce the friction velocity and Reynolds stress in the turbulent boundary layer, indicating the drag reduction effect. Strong correlation has been found between the occurrence of hairpin vortices and the momentum distribution. The number and streamwise length scale of hairpin vortices decrease over streamwise riblet surface. The correlation between number of uniform momentum zones and Reynolds number remains the same as smooth surface.
基金supported by the National Natural Science Foundation of China(Nos.52125206,52433013,52273050,and 22409008)the Beijing Natural Science Foundation(No.Z240024)+3 种基金the National Key Research and Development Program of China(No.2023YFB4202502)the China Postdoctoral Science Foundation(No.2024T170023)the Qing Lan Project,the Tencent Foundation through the Xplorer Prize,the China National Petroleum Corporation-Peking University Strategic Cooperation Project of Fundamental Research,the Sinopec Seeding Programthe Yunnan Provincial Science and Technology Project at Southwest United Graduate School(No.202302AO370013).
文摘Metal halide perovskite solar cells(PSCs)are anticipated to play a pivotal role in the next generation of photovoltaic technologies,but their unsatisfactory stability hinders further commercial applications.Particularly,numerous interfacial defects and poor mechanical adhesion at the perovskite buried interface present a critical obstacle hindering power conversion efficiency(PCE)and longterm stability of PSCs.Here,different from conventional small-molecule or linear polymer interface modifiers,we introduce a star-shaped PMMA-b-PDMAEMA(S-MD,where PMMA=poly(methyl methacrylate)and PDMAEMA=poly(dimethylaminoethyl methacrylate))polymer as a multifunctional bridge-linking polymer for simultaneous defect passivation and mechanical reinforcement at the buried interface of inverted(p-i-n)PSCs.S-MD features a three-dimensional architecture with multiple extended conjugated arms,offering multiple Lewis base functional groups(e.g.,C=O and R-N(CH_(3))_(2))with a high density of multidentate coordination sites.These groups can effectively coordinate with electron-deficient defects at the perovskite buried interface,enabling improved crystallization,reduced defect density,and enhanced interfacial adhesion.As a result,the interfacial fracture strength increases from 0.13 to 1.66 MPa.The resultant device achieves a PCE of 26.35%(certified steady-state PCE of 25.96%).The flexible device retains over 90%of its initial efficiency after 3000 flexing cycles at a curvature radius of 6 mm(R=6 mm).This work highlights a multidentate coordinating,star-shaped polymer interface strategy that offers a promising pathway toward highly efficient and stable inverted PSCs.
