We investigate the mechanism for the improvement of p-type doping efficiency in Mg-Al0.14Ga0.86N/GaN super- lattices (SLs). It is shown that the hole concentration of SLs increases by nearly an order of magnitude, f...We investigate the mechanism for the improvement of p-type doping efficiency in Mg-Al0.14Ga0.86N/GaN super- lattices (SLs). It is shown that the hole concentration of SLs increases by nearly an order of magnitude, from 1.1 × 1017 to 9.3×1017 cm-3, when an AlN interlayer is inserted to modulate the strains. SchrSdinger-Poisson self-consistent calculations suggest that such an increase could be attributed to the reduction of donor-like defects caused by the strain modulation induced by the AlN interlayer. Additionally, the donor-acceptor pair emission exhibits a remarkable decrease in intensity of the cathodoluminescence spectrumlfor SLs with an A1N interlayer. This supports the theoretical calculations and indicates that the strain modulation of SLs could be beneficial to the donor-like defect suppression as well as the p-type doping efficiency improvement.展开更多
Since a hole barrier was formed in back contact due to mismatch of work function, the back contact material for CdTe cell has been a significant research direction. The ZnTe:Cu is an ideal back contact material, which...Since a hole barrier was formed in back contact due to mismatch of work function, the back contact material for CdTe cell has been a significant research direction. The ZnTe:Cu is an ideal back contact material, which reduces the valence band discontinuity and can be used as the electron back reflection layer to inhibit interface recombination. The conductivity of ZnTe:Cu film is improved by applying RF-coupled DC sputtering and post-deposition heat treatment. The doping efficiency is computed as the ratio of free hole density and copper concentration, which can be correlated with performance for CdTe-based solar cell. The higher doping efficiency means that more copper atoms substitute for Zn sites in ZnTe lattices and less mobilized copper atoms remain which can enter into the CdTe absorber layer. Copper atoms are suspected as dominant element for CdTe-based cell degradation. After optimizing the ZnTe:Cu films, a systematic study is carried out to incorporate ZnTe:Cu film into CdTe solar cell. The EQE spectrum is kept relatively stable over the long wavelength range without decreasing. It is proved that the conduction band barrier of device with ZnTe:Cu/Au contact material has an effect on the EQE response, which works as free electron barrier and reduces the recombination rate of free carrier. According to the dark J-V data or the light J-V data in the linear region, the current indicates that the intercept gives the diode reverse saturation current. The results of ideality factor indicate that the dominant recombination occurs in the space charge region. In addition, the space charge density and depletion width of solar cell can be estimated by C-V profiling.展开更多
Molecular doping is one of the most important tools to manipulate the electrical properties of conjugated polymers for application in organic optoelectronics.The polymer crystallinity and distribution position of the ...Molecular doping is one of the most important tools to manipulate the electrical properties of conjugated polymers for application in organic optoelectronics.The polymer crystallinity and distribution position of the dopant crucially determine electrical conductivity of the doped polymer.However,in solution-mixed doping,the interplay between polymer and dopant leads to highly structural disorder of polymer and random arrangement of dopant.Here,we propose a strategy to ensure the dopant induced polarons have high charge dissociation and transport by letting the conjugated polymers aggregate in the marginal solvent solution by cooling it from higher temperature to room temperature.We select poly(3-hexylthiophene-2,5-diyl)(P3HT)solution doped by 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4TCNQ)as a model system.P3HT crystallizes in the marginal solvent,such as 1,1,2-trichloroethane(TCE)driven by the favorπ-πinteraction between planar polymer backbone.The dopant F4TCNQ enters the alkyl side chain region not theπ-πstacking region and thus guarantees high crystallinity and theπ-πinteraction of P3HT.This distribution of F4TCNQ which away from the polymer backbone to ensure higher charge dissociation and transport.Finally,we obtained a high conductivity value of 23 S/cm by doping P3HT with 20%F4TCNQ by using the marginal solvent,which is higher than doping P3HT with a disordered coil conformation in chlorobenzene(CB)of 7 S/cm,which the dopants enter both the alkyl side chain region and theπ-πstacking region.展开更多
Molecular doping is essential to improve the electrical conductivity of organic semiconductors for high-performance organic electronic devices. However, the doping efficiency is influenced by several factors, such as ...Molecular doping is essential to improve the electrical conductivity of organic semiconductors for high-performance organic electronic devices. However, the doping efficiency is influenced by several factors, such as the energy levels, energetic fluctuations, dielectric properties, and molecular packing structures of the doped films, and the underlying mechanisms for highefficiency doping are still unclear. Here, through multi-level theoretical simulations on a series of fullerene derivatives, we identify that the energetic fluctuations can play a decisive role in activating charge separation for molecular doping. In particular,the doping efficiency appears to be exponentially increased with the fluctuation of charge polarization energies. Therefore,although the charge mobility is somewhat decreased, the experimental electrical conductivity is improved with the increased energetic fluctuation. Moreover, it has been found that polarization energy fluctuation can be effectively enhanced by simply introducing side chains with greater flexibility into organic semiconductors. This article paves the way towards high-efficiency molecular doping of organic semiconductors.展开更多
Ga-doped ZnO (GZO) films are prepared on amorphous glass substrates at room temperature by radio frequency magnetron sputtering. The results reveal that the gallium doping efficiency, which will have an important in...Ga-doped ZnO (GZO) films are prepared on amorphous glass substrates at room temperature by radio frequency magnetron sputtering. The results reveal that the gallium doping efficiency, which will have an important influence on the electrical and optical properties of the film, can be governed greatly by the deposition pressure and film thickness. The position shifts of the ZnO (002) peaks in X-ray diffraction (XRD) measurements and the varied Hall mobility and carrier concentration confirms this result. The low Hall mobility is attributed to the grain boundary barrier scattering. The estimated height of barrier decreases with the increase of carrier concentration, and the trapping state density is nearly constant. According to defect formation energies and relevant chemical reactions, the photoluminescence (PL) peaks at 2.46 eV and 3.07 eV are attributed to oxygen vacancies and zinc vacancies, respectively. The substitution of more Ga atoms for Zn vacancies with the increase in film thickness is also confirmed by the PL spectrum. The obvious blueshift of the optical bandgap with an increase of carrier concentration is explained well by the Burstein Moss (BM) effect. The bandgap difference between 3.18 eV and 3.37 eV, about 0.2 eV, is attributed to the metal-semiconductor transition.展开更多
By using two sections of erbium doped fiber and a fiber optical reflector, a novel, highly efficient L-band amplifier is demonstrated with significantly power-conversion-efficiency enhancement and the gain increasing ...By using two sections of erbium doped fiber and a fiber optical reflector, a novel, highly efficient L-band amplifier is demonstrated with significantly power-conversion-efficiency enhancement and the gain increasing of as much as 13 dB.展开更多
Recent theoretical predictions and experimental findings on the transport properties of n-type SnTe have triggered extensive researches on this simple binary compound,despite the realization of n-type SnTe being a gre...Recent theoretical predictions and experimental findings on the transport properties of n-type SnTe have triggered extensive researches on this simple binary compound,despite the realization of n-type SnTe being a great challenge.Herein,Cl as a donor dopant can effectively regulate the position of Fermi level in Sn_(0.6)Pb_(0.4)Te matrix and successfully achieve the n-type transport behavior in SnTe.An outstanding power factor of~14.7μW·cm^(-1)·K^(-2) at 300 K was obtained for Cl-doped Sn_(0.6)Pb_(0.4)Te sample.By combining the experimental analysis with theoretical calculations,the transport properties of n-type SnTe thermoelectrics doped with different halogen dopants(Cl,Br,and I)were then systematically investigated and estimated.The results demonstrated that Br and I had better doping efficiencies compared with Cl,which contributed to the well-optimized carrier concentrations of~1.03×10^(19)and~1.11×10^(19)cm^(-3)at 300 K,respectively.The improved n-type carrier concentrations effectively lead to the significant enhancement on the thermoelectric performance of n-type SnTe.Our study further promoted the experimental progress and deep interpretation of the transport features in n-type SnTe thermoelectrics.The present results could also be crucial for the development of n-type counterparts for SnTe-based thermoelectric devices.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61076012,61076013,and 51102003)the National High Technology Research and Development Program of China (Grant No. 2007AA03Z403)+1 种基金the Specialized Research Fund for the Doctoral Program of Higher Education,China (Grant No. 20100001120014)the National Basic Research Program of China (Grant No. 2012CB619304)
文摘We investigate the mechanism for the improvement of p-type doping efficiency in Mg-Al0.14Ga0.86N/GaN super- lattices (SLs). It is shown that the hole concentration of SLs increases by nearly an order of magnitude, from 1.1 × 1017 to 9.3×1017 cm-3, when an AlN interlayer is inserted to modulate the strains. SchrSdinger-Poisson self-consistent calculations suggest that such an increase could be attributed to the reduction of donor-like defects caused by the strain modulation induced by the AlN interlayer. Additionally, the donor-acceptor pair emission exhibits a remarkable decrease in intensity of the cathodoluminescence spectrumlfor SLs with an A1N interlayer. This supports the theoretical calculations and indicates that the strain modulation of SLs could be beneficial to the donor-like defect suppression as well as the p-type doping efficiency improvement.
基金Project supported by the Research Foundation of Institute of Electrical Engineering, Chinese Academy of Sciences, (Grant No. Y710411CSB)the Lujiaxi International Team Project of Chinese Academy of Sciences (Grant No. GJTD2018-05)+1 种基金the Chinese Academy of Sciences President’s International Fellowship Initiative (Grant No. 2020VEC0008)the Fund from the Institute of Electrical Engineering and Advanced Electromagnetic Drive Technology, Qilu Zhongke。
文摘Since a hole barrier was formed in back contact due to mismatch of work function, the back contact material for CdTe cell has been a significant research direction. The ZnTe:Cu is an ideal back contact material, which reduces the valence band discontinuity and can be used as the electron back reflection layer to inhibit interface recombination. The conductivity of ZnTe:Cu film is improved by applying RF-coupled DC sputtering and post-deposition heat treatment. The doping efficiency is computed as the ratio of free hole density and copper concentration, which can be correlated with performance for CdTe-based solar cell. The higher doping efficiency means that more copper atoms substitute for Zn sites in ZnTe lattices and less mobilized copper atoms remain which can enter into the CdTe absorber layer. Copper atoms are suspected as dominant element for CdTe-based cell degradation. After optimizing the ZnTe:Cu films, a systematic study is carried out to incorporate ZnTe:Cu film into CdTe solar cell. The EQE spectrum is kept relatively stable over the long wavelength range without decreasing. It is proved that the conduction band barrier of device with ZnTe:Cu/Au contact material has an effect on the EQE response, which works as free electron barrier and reduces the recombination rate of free carrier. According to the dark J-V data or the light J-V data in the linear region, the current indicates that the intercept gives the diode reverse saturation current. The results of ideality factor indicate that the dominant recombination occurs in the space charge region. In addition, the space charge density and depletion width of solar cell can be estimated by C-V profiling.
基金financially supported by the National Natural Science Foundation of China(No.51933010)。
文摘Molecular doping is one of the most important tools to manipulate the electrical properties of conjugated polymers for application in organic optoelectronics.The polymer crystallinity and distribution position of the dopant crucially determine electrical conductivity of the doped polymer.However,in solution-mixed doping,the interplay between polymer and dopant leads to highly structural disorder of polymer and random arrangement of dopant.Here,we propose a strategy to ensure the dopant induced polarons have high charge dissociation and transport by letting the conjugated polymers aggregate in the marginal solvent solution by cooling it from higher temperature to room temperature.We select poly(3-hexylthiophene-2,5-diyl)(P3HT)solution doped by 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4TCNQ)as a model system.P3HT crystallizes in the marginal solvent,such as 1,1,2-trichloroethane(TCE)driven by the favorπ-πinteraction between planar polymer backbone.The dopant F4TCNQ enters the alkyl side chain region not theπ-πstacking region and thus guarantees high crystallinity and theπ-πinteraction of P3HT.This distribution of F4TCNQ which away from the polymer backbone to ensure higher charge dissociation and transport.Finally,we obtained a high conductivity value of 23 S/cm by doping P3HT with 20%F4TCNQ by using the marginal solvent,which is higher than doping P3HT with a disordered coil conformation in chlorobenzene(CB)of 7 S/cm,which the dopants enter both the alkyl side chain region and theπ-πstacking region.
基金supported by the Beijing Natural Science Foundation (2244083)the National Natural Science Foundation of China (22173108)+1 种基金the Ministry of Science and Technology of China (2018YFA0703200)the Youth Innovation Promotion Association CAS (2023037)。
文摘Molecular doping is essential to improve the electrical conductivity of organic semiconductors for high-performance organic electronic devices. However, the doping efficiency is influenced by several factors, such as the energy levels, energetic fluctuations, dielectric properties, and molecular packing structures of the doped films, and the underlying mechanisms for highefficiency doping are still unclear. Here, through multi-level theoretical simulations on a series of fullerene derivatives, we identify that the energetic fluctuations can play a decisive role in activating charge separation for molecular doping. In particular,the doping efficiency appears to be exponentially increased with the fluctuation of charge polarization energies. Therefore,although the charge mobility is somewhat decreased, the experimental electrical conductivity is improved with the increased energetic fluctuation. Moreover, it has been found that polarization energy fluctuation can be effectively enhanced by simply introducing side chains with greater flexibility into organic semiconductors. This article paves the way towards high-efficiency molecular doping of organic semiconductors.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61076007 and 11174348)the National Basic Research Program of China (Grant Nos. 2009CB929404 and 2011CB302002)the Knowledge Innovation Project of the Chinese Academy of Sciences
文摘Ga-doped ZnO (GZO) films are prepared on amorphous glass substrates at room temperature by radio frequency magnetron sputtering. The results reveal that the gallium doping efficiency, which will have an important influence on the electrical and optical properties of the film, can be governed greatly by the deposition pressure and film thickness. The position shifts of the ZnO (002) peaks in X-ray diffraction (XRD) measurements and the varied Hall mobility and carrier concentration confirms this result. The low Hall mobility is attributed to the grain boundary barrier scattering. The estimated height of barrier decreases with the increase of carrier concentration, and the trapping state density is nearly constant. According to defect formation energies and relevant chemical reactions, the photoluminescence (PL) peaks at 2.46 eV and 3.07 eV are attributed to oxygen vacancies and zinc vacancies, respectively. The substitution of more Ga atoms for Zn vacancies with the increase in film thickness is also confirmed by the PL spectrum. The obvious blueshift of the optical bandgap with an increase of carrier concentration is explained well by the Burstein Moss (BM) effect. The bandgap difference between 3.18 eV and 3.37 eV, about 0.2 eV, is attributed to the metal-semiconductor transition.
文摘By using two sections of erbium doped fiber and a fiber optical reflector, a novel, highly efficient L-band amplifier is demonstrated with significantly power-conversion-efficiency enhancement and the gain increasing of as much as 13 dB.
基金supported by the National Natural Science Foundation of China(No.52002042)the National Postdoctoral Program for Innovative Talents(No.BX20200028)+3 种基金the National Key Research and Development Program of China(No.2018YFA0702100)China Postdoctoral Science Foundation(No.2021M690280)the Natural Science Foundation of Chongqing,China(No.cstc2019jcyj-msxmX0554)the support from the National Science Fund for Distinguished Young Scholars(No.51925101)。
文摘Recent theoretical predictions and experimental findings on the transport properties of n-type SnTe have triggered extensive researches on this simple binary compound,despite the realization of n-type SnTe being a great challenge.Herein,Cl as a donor dopant can effectively regulate the position of Fermi level in Sn_(0.6)Pb_(0.4)Te matrix and successfully achieve the n-type transport behavior in SnTe.An outstanding power factor of~14.7μW·cm^(-1)·K^(-2) at 300 K was obtained for Cl-doped Sn_(0.6)Pb_(0.4)Te sample.By combining the experimental analysis with theoretical calculations,the transport properties of n-type SnTe thermoelectrics doped with different halogen dopants(Cl,Br,and I)were then systematically investigated and estimated.The results demonstrated that Br and I had better doping efficiencies compared with Cl,which contributed to the well-optimized carrier concentrations of~1.03×10^(19)and~1.11×10^(19)cm^(-3)at 300 K,respectively.The improved n-type carrier concentrations effectively lead to the significant enhancement on the thermoelectric performance of n-type SnTe.Our study further promoted the experimental progress and deep interpretation of the transport features in n-type SnTe thermoelectrics.The present results could also be crucial for the development of n-type counterparts for SnTe-based thermoelectric devices.