Based on a pseudo-spectral large eddy simulation (LES) model, an LES model with an anisotropy turbulent kinetic energy (TKE) closure model and an explicit multi-stage third-order Runge-Kutta scheme is established. The...Based on a pseudo-spectral large eddy simulation (LES) model, an LES model with an anisotropy turbulent kinetic energy (TKE) closure model and an explicit multi-stage third-order Runge-Kutta scheme is established. The modeling and analysis show that the LES model can simulate the planetary boundary layer (PBL) with a uniform underlying surface under various stratifications very well. Then, similar to the description of a forest canopy, the drag term on momentum and the production term of TKE by subgrid city buildings are introduced into the LES equations to account for the area-averaged effect of the subgrid urban canopy elements and to simulate the meteorological fields of the urban boundary layer (UBL). Numerical experiments and comparison analysis show that: (1) the result from the LES of the UBL with a proposed formula for the drag coefficient is consistent and comparable with that from wind tunnel experiments and an urban subdomain scale model; (2) due to the effect of urban buildings, the wind velocity near the canopy is decreased, turbulence is intensified, TKE, variance, and momentum flux are increased, the momentum and heat flux at the top of the PBL are increased, and the development of the PBL is quickened; (3) the height of the roughness sublayer (RS) of the actual city buildings is the maximum building height (1.5-3 times the mean building height), and a constant flux layer (CFL) exists in the lower part of the UBL.展开更多
In this study,large-area(6-cm diameter)Teflon polytetrafluoroethylene(PTFE)discs of different thicknesses(0.2-,0.5-and 1-mm)were negatively and positively charged by using the“modified single point-to-plane corona po...In this study,large-area(6-cm diameter)Teflon polytetrafluoroethylene(PTFE)discs of different thicknesses(0.2-,0.5-and 1-mm)were negatively and positively charged by using the“modified single point-to-plane corona poling rotating system”.The effects of some crucial parameters of the PTFE disc as well as the modified corona poling rotating system on the PTFE surface potential uniformity such as.(a)PTFE disc thickness,(b)PTFE disc polarity and(c)needle-to-PTFE disc distance were successfully reported.Accordingly,closer needle-to-PTFE disc distance,positive charging mode and thinner PTFE disc provided a better PTFE surface potential uniformity.However,the effects of PTFE charge polarity and needle distance on the electrostatic charge potential uniformity were much more remarkable in comparison with the effects of PTFE thickness.Additionally,the surface potential distribution profiles of charged PTFE discs were totally flat and independent of the PTFE thickness at 5-and 13-mm needle distances for the negative and positive charging modes,respectively.At the optimized charging conditions,large-area PTFE electret disc(0.5-mm-thick)with positive uniform surface charge potential especially at the edges up to1.8 kV with stability up to 77 days studied was produced by applying a new multiple heat treatment protocol to the PTFE disc for radon dosimetry.As also observed in this study,the sensitivity of PTFE electret dosimeters to a defined radon gas concentration increases as the PTFE thickness increases.Meanwhile,0.5-mm-thick PTFE electret disc produced was selected to be used as a high quality electret dosimeter with acceptable and superior parameters for different applications in particular medium-term radiation dosimetry in both low and high dose rate ionizing radiation fields.展开更多
The self-assembled monolayer(SAM)based on(2-(9H-carbazol-9-yl)ethyl)phosphonic acid(2PACz)deri-vatives is a promising alternative to poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate)(PEDOT:PSS)for application t...The self-assembled monolayer(SAM)based on(2-(9H-carbazol-9-yl)ethyl)phosphonic acid(2PACz)deri-vatives is a promising alternative to poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate)(PEDOT:PSS)for application to hole transport layers(HTLs)in organic solar cells(OSCs).Herein,based on MeO-4PACz,two new molecules of MeOF-4PACz and F-4PACz were designed and synthesized by replacing one or two methoxy groups of MeO-4PACz with fluorine atoms,respectively.The introduction of fluorine atoms enhances the dipole moments of SAMs,which is favorable to downshifting the work function(WF)of indium tin oxide(ITO)/SAM electrodes to achieve ideal energy-level alignment with the highest occupied molecular orbital(HOMO)energy level of the donor,and for increasing the intermolecular interaction that improves the arrangement of SAMs on the ITO surface.Compared with MeO-4PACz,the asymmetric molecule MeOF-4PACz with a methoxy substituent replaced by a fluorine atom exhibits a more uniform distribution on the ITO surface,which effectively reduces the contact defects with the active layer and suppresses the nonradiative recombination.In addition,the deeper WF of ITO/MeOF-4PACz reduces the voltage losses.The suitable WF compatibility and superior surface uniformity of the electrode of ITO/MeOF-4PACz to ITO/MeO-4PACz and ITO/F-4PACz lead to a lower hole-injection barrier and suppressed interfacial nonradiative recombination of the OSCs.Consequently,the OSCs based on PM6:Y6 with MeOF-4PACz as HTL exhibit a substantial improvement in power conversion efficiency(PCE)from 17.11%for the device with PEDOT:PSS as HTL to 19.14%.It is worth noting that PM6:Y6 is currently the most representative active layer,and 19.14%is a record high efficiency for the binary OSCs based on PM6:Y6 so far.In addition,the PCE values of the OSCs based on PM6:BTP-eC9 and PM6:CH1007 with MeOF-4PACz as HTL are also significantly improved to 19.48%(certified as 19.36%)and 18.33%,respectively,which indicates the broad compatibility of MeOF-4PACz HTL with various mainstream active layer systems of the OSCs.Overall,this work underscores the significant impact of designing and modifying the molecular structure of the SAM HTLs on further improving the photovoltaic performance of OSCs.展开更多
基金The research was supported by the National Natural Science Foundation of China under Grant Nos.40333027 and 40075004.
文摘Based on a pseudo-spectral large eddy simulation (LES) model, an LES model with an anisotropy turbulent kinetic energy (TKE) closure model and an explicit multi-stage third-order Runge-Kutta scheme is established. The modeling and analysis show that the LES model can simulate the planetary boundary layer (PBL) with a uniform underlying surface under various stratifications very well. Then, similar to the description of a forest canopy, the drag term on momentum and the production term of TKE by subgrid city buildings are introduced into the LES equations to account for the area-averaged effect of the subgrid urban canopy elements and to simulate the meteorological fields of the urban boundary layer (UBL). Numerical experiments and comparison analysis show that: (1) the result from the LES of the UBL with a proposed formula for the drag coefficient is consistent and comparable with that from wind tunnel experiments and an urban subdomain scale model; (2) due to the effect of urban buildings, the wind velocity near the canopy is decreased, turbulence is intensified, TKE, variance, and momentum flux are increased, the momentum and heat flux at the top of the PBL are increased, and the development of the PBL is quickened; (3) the height of the roughness sublayer (RS) of the actual city buildings is the maximum building height (1.5-3 times the mean building height), and a constant flux layer (CFL) exists in the lower part of the UBL.
文摘In this study,large-area(6-cm diameter)Teflon polytetrafluoroethylene(PTFE)discs of different thicknesses(0.2-,0.5-and 1-mm)were negatively and positively charged by using the“modified single point-to-plane corona poling rotating system”.The effects of some crucial parameters of the PTFE disc as well as the modified corona poling rotating system on the PTFE surface potential uniformity such as.(a)PTFE disc thickness,(b)PTFE disc polarity and(c)needle-to-PTFE disc distance were successfully reported.Accordingly,closer needle-to-PTFE disc distance,positive charging mode and thinner PTFE disc provided a better PTFE surface potential uniformity.However,the effects of PTFE charge polarity and needle distance on the electrostatic charge potential uniformity were much more remarkable in comparison with the effects of PTFE thickness.Additionally,the surface potential distribution profiles of charged PTFE discs were totally flat and independent of the PTFE thickness at 5-and 13-mm needle distances for the negative and positive charging modes,respectively.At the optimized charging conditions,large-area PTFE electret disc(0.5-mm-thick)with positive uniform surface charge potential especially at the edges up to1.8 kV with stability up to 77 days studied was produced by applying a new multiple heat treatment protocol to the PTFE disc for radon dosimetry.As also observed in this study,the sensitivity of PTFE electret dosimeters to a defined radon gas concentration increases as the PTFE thickness increases.Meanwhile,0.5-mm-thick PTFE electret disc produced was selected to be used as a high quality electret dosimeter with acceptable and superior parameters for different applications in particular medium-term radiation dosimetry in both low and high dose rate ionizing radiation fields.
基金supported by the National Key Research and Development Program of China(grant no.2019YFA0705900)the National Natural Science Foundation of China(grant nos.52203248,52103243,52173188)+3 种基金the Key Research Program of the Chinese Academy of Sciences(grant no.XDPB13)the Strategic Priority Research Program of the Chinese Academy of Sciences(grant no.XDB 0520102)the Basic and Applied Basic Research Major Program of Guangdong Province(grant no.2019B030302007)the Beijing National Laboratory for Molecular Science(grant no.2019BMS20017)。
文摘The self-assembled monolayer(SAM)based on(2-(9H-carbazol-9-yl)ethyl)phosphonic acid(2PACz)deri-vatives is a promising alternative to poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate)(PEDOT:PSS)for application to hole transport layers(HTLs)in organic solar cells(OSCs).Herein,based on MeO-4PACz,two new molecules of MeOF-4PACz and F-4PACz were designed and synthesized by replacing one or two methoxy groups of MeO-4PACz with fluorine atoms,respectively.The introduction of fluorine atoms enhances the dipole moments of SAMs,which is favorable to downshifting the work function(WF)of indium tin oxide(ITO)/SAM electrodes to achieve ideal energy-level alignment with the highest occupied molecular orbital(HOMO)energy level of the donor,and for increasing the intermolecular interaction that improves the arrangement of SAMs on the ITO surface.Compared with MeO-4PACz,the asymmetric molecule MeOF-4PACz with a methoxy substituent replaced by a fluorine atom exhibits a more uniform distribution on the ITO surface,which effectively reduces the contact defects with the active layer and suppresses the nonradiative recombination.In addition,the deeper WF of ITO/MeOF-4PACz reduces the voltage losses.The suitable WF compatibility and superior surface uniformity of the electrode of ITO/MeOF-4PACz to ITO/MeO-4PACz and ITO/F-4PACz lead to a lower hole-injection barrier and suppressed interfacial nonradiative recombination of the OSCs.Consequently,the OSCs based on PM6:Y6 with MeOF-4PACz as HTL exhibit a substantial improvement in power conversion efficiency(PCE)from 17.11%for the device with PEDOT:PSS as HTL to 19.14%.It is worth noting that PM6:Y6 is currently the most representative active layer,and 19.14%is a record high efficiency for the binary OSCs based on PM6:Y6 so far.In addition,the PCE values of the OSCs based on PM6:BTP-eC9 and PM6:CH1007 with MeOF-4PACz as HTL are also significantly improved to 19.48%(certified as 19.36%)and 18.33%,respectively,which indicates the broad compatibility of MeOF-4PACz HTL with various mainstream active layer systems of the OSCs.Overall,this work underscores the significant impact of designing and modifying the molecular structure of the SAM HTLs on further improving the photovoltaic performance of OSCs.
