The large volumetric variations experienced by metal selenides within conversion reaction result in inferior rate capability and cycling stability,ultimately hindering the achievement of superior electrochemical perfo...The large volumetric variations experienced by metal selenides within conversion reaction result in inferior rate capability and cycling stability,ultimately hindering the achievement of superior electrochemical performance.Herein,metallic Cu_(2)Se encapsulated with N-doped carbon(Cu_(2)Se@NC)was prepared using Cu_(2)O nanocubes as templates through a combination of dopamine polymerization and hightemperature selenization.The unique nanocubic structure and uniform N-doped carbon coating could shorten the ion transport distance,accelerate electron/charge diffusion,and suppress volume variation,ultimately ensuring Cu_(2)Se@NC with excellent electrochemical performance in sodium ion batteries(SIBs)and potassium ion batteries(PIBs).The composite exhibited excellent rate performance(187.7 mA h g^(-1)at 50 A g^(-1)in SIBs and 179.4 mA h g^(-1)at 5 A g^(-1)in PIBs)and cyclic stability(246,8 mA h g^(-1)at 10 A g^(-1)in SIBs over 2500 cycles).The reaction mechanism of intercalation combined with conversion in both SIBs and PIBs was disclosed by in situ X-ray diffraction(XRD)and ex situ transmission electron microscope(TEM).In particular,the final products in PIBs of K_(2)Se and K_(2)Se_(3)species were determined after discharging,which is different from that in SIBs with the final species of Na_(2)Se.The density functional theory calculation showed that carbon induces strong coupling and charge interactions with Cu_(2)Se,leading to the introduction of built-in electric field on heterojunction to improve electron mobility.Significantly,the theoretical calculations discovered that the underlying cause for the relatively superior rate capability in SIBs to that in PIBs is the agile Na~+diffusion with low energy barrier and moderate adsorption energy.These findings offer theoretical support for in-depth understanding of the performance differences of Cu-based materials in different ion storage systems.展开更多
The beneficial effect of the alkali metals such as Na and K on the Cu（In.Ga）Se2 （CIGS） and Cu2ZnSn（S,Se）4 （CZTSSe） solar cells has been extensively investigated in the past two decades, however, in most of the...The beneficial effect of the alkali metals such as Na and K on the Cu（In.Ga）Se2 （CIGS） and Cu2ZnSn（S,Se）4 （CZTSSe） solar cells has been extensively investigated in the past two decades, however, in most of the studies the alkali metals were treated as dopants. Several recent studies have showed that the alkali metals may not only act as dopants but also form secondary phases in the absorber layer or on the surfaces of the films. Using the first-principles calculations, we screened out the most probable secondary phases of Na and K in CIGS and CZTSSe, and studied their electronic structures and optical properties. We found that all these alkali chalcogenide compounds have larger band gaps and lower VBM levels than CIGS and CZTSSe, because the existence of strong p-d coupling in CIS and CZTS pushes the valence band maximum （VBM） level up and reduces the band-gaps, while there is no such p-d coupling in these alkali chalcogenides. This band alignment repels the photo-generated holes from the secondary phases and prevents the electron-hole recombination. Moreover, the study on the optical properties of the secondary phases showed that the absorption coefficients of these alkali chalcogenides are much lower than those of CIGS and CZTSSe in the energy range of 0-3.4eV, which means that the alkali chalcogenides may not influence the absorption of solar light. Since the alkali metal dopants can passivate the grain boundaries and increase the hole carrier concentration, and meanwhile their related secondary phases have innocuous effect on the optical absorption and band alignment, we can understand why the alkali metal dopants can improve the CIGS and CZTSSe solar cell performance.展开更多
Low-dimensional halide perovskites have become the most promising candidates for X-ray imaging,yet the issues of the poor chemical stability of hybrid halide perovskite,the high poisonousness of lead halides and the r...Low-dimensional halide perovskites have become the most promising candidates for X-ray imaging,yet the issues of the poor chemical stability of hybrid halide perovskite,the high poisonousness of lead halides and the relatively low detectivity of the lead-free halide perovskites which seriously restrain its commercialization.Here,we developed a solution inverse temperature crystal growth(ITCG)method to bring-up high quality Cs_(3)Cu_(2)I_(5)crystals with large size of centimeter order,in which the oleic acid(OA)is introduced as an antioxidative ligand to inhibit the oxidation of cuprous ions effieiently,as well as to decelerate the crystallization rate remarkalby.Based on these fine crystals,the vapor deposition technique is empolyed to prepare high quality Cs_(3)Cu_(2)I_(5)films for efficient X-ray imaging.Smooth surface morphology,high light yields and short decay time endow the Cs_(3)Cu_(2)I_(5)films with strong radioluminescence,high resolution(12 lp/mm),low detection limits(53 nGyair/s)and desirable stability.Subsequently,the Cs_(3)Cu_(2)I_(5)films have been applied to the practical radiography which exhibit superior X-ray imaging performance.Our work provides a paradigm to fabricate nonpoisonous and chemically stable inorganic halide perovskite for X-ray imaging.展开更多
CuIn（S,Se）2 thin films were prepared by thermal crystallization of co-sputtered Cu-In alloy precursors in S/Se atmosphere. In-depth compositional uniformity is an important prereq- uisite for obtaining device-qualit...CuIn（S,Se）2 thin films were prepared by thermal crystallization of co-sputtered Cu-In alloy precursors in S/Se atmosphere. In-depth compositional uniformity is an important prereq- uisite for obtaining device-quality CuIn（S,Se）2 absorber thin films. In order to figure out the influence of heat treatments on in-depth composition uniformity of CuIn（S,Se）2 thin films, two kinds of reaction temperature profiles were investigated. One process is ＂one step profile＂, referring to formation of CuIn（S,Se）2 thin films just at elevated temperature （e.g. 500 ℃）. The other is ＂two step profile＂, which allows for slow diffusion of S and Se elements into the alloy precursors at a low temperature before the formation and re-crystallization of CuIn（S,Se）2 thin films at higher temperature （e.g. first 250 ℃ then 500 ℃）. X-ray diffrac- tion studies reveal that there is a discrepancy in the shape of （112） peak. Samples annealed with ＂one step profile＂ have splits on （112） peaks, while samples annealed with ＂two step profile＂ have relatively symmetrical （112） peaks. Grazing incident X-ray diffraction and en- ergy dispersive spectrum measurements of samples successively etched in bromine methanol show that CuIn（S,Se）2 thin films have better in-depth composition uniformity after ＂two step profile＂ annealing. The reaction mechanism during the two thermal processing was also investigated by X-ray diffraction and Raman spectra.展开更多
The environmentally friendly Cu_(2)ZnSn(S,Se)_(4)(CZTSSe) compounds are promising direct bandgap materials for application in thin film solar cells, but the spontaneous surface defects disordering would lead to large ...The environmentally friendly Cu_(2)ZnSn(S,Se)_(4)(CZTSSe) compounds are promising direct bandgap materials for application in thin film solar cells, but the spontaneous surface defects disordering would lead to large open-circuit voltage deficit(V_(oc,deficit)) and significantly limit kesterite photovoltaics performance,primarily arising from the generated more recombination centers and insufficient p to n conversion at p-n junction. Herein, we establish a surface defects ordering structure in CZTSSe system via local substitution of Cu by Ag to suppress disordered Cu_(Zn) defects and generate benign n-type Zn_(Ag) donors. Taking advantage of the decreased annealing temperature of Ag F post deposition treatment(PDT), the high concentration of Ag incorporated into surface absorber facilitates the formation of surface ordered defect environment similar to that of efficient CIGS PV. The manipulation of highly doped surface structure could effectively reduce recombination centers, increase depletion region width and enlarge the band bending near p-n junction. As a result, the Ag F-PDT device finally achieves maximum efficiency of 12.34% with enhanced V_(oc) of 0.496 V. These results offer a new solution route in surface defects and energy-level engineering, and open the way to build up high quality p-n junction for future development of kesterite technology.展开更多
It is very important to understand why a small amount of alkali metal doping in Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)solar cells can improve the conversion efficiency.In this work,Na-doped CZTSSe is prepared by a simple soluti...It is very important to understand why a small amount of alkali metal doping in Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)solar cells can improve the conversion efficiency.In this work,Na-doped CZTSSe is prepared by a simple solution method,and then the effects on the surface properties of the absorber layer,the buffer layer growth,and the modifications of the solar cell performance induced by the Na doping are studied.The surface of the absorber layer is more Cu-depletion and less roughness due to the Na doping.In addition,the contact angle of the surface increases because of Na doping.As a consequence,the thickness of the CdS buffer layer is significantly reduced and the optical losses in the CdS buffer layer are decreased.The difference of quasi-Fermi levels(EFn-EFp) increases with a small amount of Na doping in the CZTSSe solar cell,so that open circuit voltage(VOC) increased significantly.This work offers new insights into the effects of Na doping on CZTSSe via a solution-based approach and provides a deeper understanding of the origin of the efficiency improvement of Na-doped CZTSSe thin film solar cells.展开更多
The nanoporous Cu_(2-x)Se with Cu(Se-5%)surface catalysts were prepared through in situ dynamic restructuring strategy during the electrochemical process,which achieves highly selective electrochemical CO_(2) reductio...The nanoporous Cu_(2-x)Se with Cu(Se-5%)surface catalysts were prepared through in situ dynamic restructuring strategy during the electrochemical process,which achieves highly selective electrochemical CO_(2) reduction to methanol.In situ and quasi-operando spectroscopic results provide a deep insight into the catalytic active centres of reconstructed heterogeneous catalysts for CO_(2) electroreduction.展开更多
Thin films of copper indium gallium selenide Cu（In,Ga）Se2 （CIGS） were prepared by sequential elemental layer deposition in vacuum at room temperature. The as-deposited films were heated in vacuum for compound form...Thin films of copper indium gallium selenide Cu（In,Ga）Se2 （CIGS） were prepared by sequential elemental layer deposition in vacuum at room temperature. The as-deposited films were heated in vacuum for compound formation, and were studied at temperature as high as 1250℃ for the first time. These films were concurrently studied for their structural properties by X-ray diffraction （XRD） technique. The XRD analyses include phase transition studies, grain size variation and microstrain measurements with the reaction temperature and time.It has been observed that there are three distinct regions of variation in all these parameters. These regions belong to three temperature regimes： 〈450℃, 450-950℃, and 〉950℃. It is also seen that the compound formation starts at 250℃, with ternary phases appearing at 350℃ or above. Whereas, there is another phase shift at 950℃ without any preference to the quaternary compound.展开更多
Photo-generated carrier recombination loss at the CZTSSe/Cd S front interface is a key issue to the opencircuit voltage(V_(OC)) deficit of Cu_(2)ZnSnS_(x)Se_(4-x)(CZTSSe) solar cells. Here, by the aid of an easy-handl...Photo-generated carrier recombination loss at the CZTSSe/Cd S front interface is a key issue to the opencircuit voltage(V_(OC)) deficit of Cu_(2)ZnSnS_(x)Se_(4-x)(CZTSSe) solar cells. Here, by the aid of an easy-handling spin-coating method, a thin PCBM([6,6]-phenyl-C61-butyric acid methyl ester) layer as an electron extraction layer has been introduced on the top of CdS buffer layer to modify CZTSSe/CdS/ZnO-ITO(In_(2)O_(3):Sn) interfacial properties. Based on Sn^(4+)/DMSO(dimethyl sulfoxide) solution system, a totalarea efficiency of 12.87% with a VOC of 529 m V has been achieved. A comprehensive investigation on the influence of PCBM layer on carrier extraction, transportation and recombination processes has been carried out. It is found that the PCBM layer can smooth over the Cd S film roughness, thus beneficial for a dense and flat window layer. Furthermore, this CZTSSe/Cd S/PCBM heterostructure can accelerate carrier separation and extraction and block holes from the front interface as well, which is mainly ascribed to the downward band bending of the absorber and a widened space charge region. Our work provides a feasible way to improve the front interfacial property and the cell performance of CZTSSe solar cells by the aid of organic interfacial materials.展开更多
基金The Natural Science Foundation of Henan Province(222300420083)the Opening Foundation of State Key Laboratory of Chemistry and Utilization of Carbon-based Energy Resource of Xinjiang University(KFKT2021004)。
文摘The large volumetric variations experienced by metal selenides within conversion reaction result in inferior rate capability and cycling stability,ultimately hindering the achievement of superior electrochemical performance.Herein,metallic Cu_(2)Se encapsulated with N-doped carbon(Cu_(2)Se@NC)was prepared using Cu_(2)O nanocubes as templates through a combination of dopamine polymerization and hightemperature selenization.The unique nanocubic structure and uniform N-doped carbon coating could shorten the ion transport distance,accelerate electron/charge diffusion,and suppress volume variation,ultimately ensuring Cu_(2)Se@NC with excellent electrochemical performance in sodium ion batteries(SIBs)and potassium ion batteries(PIBs).The composite exhibited excellent rate performance(187.7 mA h g^(-1)at 50 A g^(-1)in SIBs and 179.4 mA h g^(-1)at 5 A g^(-1)in PIBs)and cyclic stability(246,8 mA h g^(-1)at 10 A g^(-1)in SIBs over 2500 cycles).The reaction mechanism of intercalation combined with conversion in both SIBs and PIBs was disclosed by in situ X-ray diffraction(XRD)and ex situ transmission electron microscope(TEM).In particular,the final products in PIBs of K_(2)Se and K_(2)Se_(3)species were determined after discharging,which is different from that in SIBs with the final species of Na_(2)Se.The density functional theory calculation showed that carbon induces strong coupling and charge interactions with Cu_(2)Se,leading to the introduction of built-in electric field on heterojunction to improve electron mobility.Significantly,the theoretical calculations discovered that the underlying cause for the relatively superior rate capability in SIBs to that in PIBs is the agile Na~+diffusion with low energy barrier and moderate adsorption energy.These findings offer theoretical support for in-depth understanding of the performance differences of Cu-based materials in different ion storage systems.
基金supported by the National Natural Science Foundation of China(NSFC)under grant nos.61574059 and 61722402the National Key Research and Development Program of China(2016YFB0700700)+1 种基金Shu-Guang program(15SG20)CC of ECNU
文摘The beneficial effect of the alkali metals such as Na and K on the Cu（In.Ga）Se2 （CIGS） and Cu2ZnSn（S,Se）4 （CZTSSe） solar cells has been extensively investigated in the past two decades, however, in most of the studies the alkali metals were treated as dopants. Several recent studies have showed that the alkali metals may not only act as dopants but also form secondary phases in the absorber layer or on the surfaces of the films. Using the first-principles calculations, we screened out the most probable secondary phases of Na and K in CIGS and CZTSSe, and studied their electronic structures and optical properties. We found that all these alkali chalcogenide compounds have larger band gaps and lower VBM levels than CIGS and CZTSSe, because the existence of strong p-d coupling in CIS and CZTS pushes the valence band maximum （VBM） level up and reduces the band-gaps, while there is no such p-d coupling in these alkali chalcogenides. This band alignment repels the photo-generated holes from the secondary phases and prevents the electron-hole recombination. Moreover, the study on the optical properties of the secondary phases showed that the absorption coefficients of these alkali chalcogenides are much lower than those of CIGS and CZTSSe in the energy range of 0-3.4eV, which means that the alkali chalcogenides may not influence the absorption of solar light. Since the alkali metal dopants can passivate the grain boundaries and increase the hole carrier concentration, and meanwhile their related secondary phases have innocuous effect on the optical absorption and band alignment, we can understand why the alkali metal dopants can improve the CIGS and CZTSSe solar cell performance.
基金the financially support of the National Natural Science Foundation of China(12164051)the Joint Foundation of Provincial Science and Technology Department-Double First-class Construction of Yunnan University(2019FY003016)+4 种基金the Young Top Talent Project of Yunnan Province(YNWR-QNBJ-2018-229)the financially support by Yunnan Major Scientific and Technological Projects(202202AG050016)Advanced Analysis and Measurement Center of Yunnan University for the sample characterization service and the Postgraduate Research and Innovation Foundation of Yunnan University(2021Y036)the financially support of the National Natural Science Foundation of China(62064013)the Application Basic Research Project of Yunnan Province[2019FB130]。
文摘Low-dimensional halide perovskites have become the most promising candidates for X-ray imaging,yet the issues of the poor chemical stability of hybrid halide perovskite,the high poisonousness of lead halides and the relatively low detectivity of the lead-free halide perovskites which seriously restrain its commercialization.Here,we developed a solution inverse temperature crystal growth(ITCG)method to bring-up high quality Cs_(3)Cu_(2)I_(5)crystals with large size of centimeter order,in which the oleic acid(OA)is introduced as an antioxidative ligand to inhibit the oxidation of cuprous ions effieiently,as well as to decelerate the crystallization rate remarkalby.Based on these fine crystals,the vapor deposition technique is empolyed to prepare high quality Cs_(3)Cu_(2)I_(5)films for efficient X-ray imaging.Smooth surface morphology,high light yields and short decay time endow the Cs_(3)Cu_(2)I_(5)films with strong radioluminescence,high resolution(12 lp/mm),low detection limits(53 nGyair/s)and desirable stability.Subsequently,the Cs_(3)Cu_(2)I_(5)films have been applied to the practical radiography which exhibit superior X-ray imaging performance.Our work provides a paradigm to fabricate nonpoisonous and chemically stable inorganic halide perovskite for X-ray imaging.
文摘CuIn（S,Se）2 thin films were prepared by thermal crystallization of co-sputtered Cu-In alloy precursors in S/Se atmosphere. In-depth compositional uniformity is an important prereq- uisite for obtaining device-quality CuIn（S,Se）2 absorber thin films. In order to figure out the influence of heat treatments on in-depth composition uniformity of CuIn（S,Se）2 thin films, two kinds of reaction temperature profiles were investigated. One process is ＂one step profile＂, referring to formation of CuIn（S,Se）2 thin films just at elevated temperature （e.g. 500 ℃）. The other is ＂two step profile＂, which allows for slow diffusion of S and Se elements into the alloy precursors at a low temperature before the formation and re-crystallization of CuIn（S,Se）2 thin films at higher temperature （e.g. first 250 ℃ then 500 ℃）. X-ray diffrac- tion studies reveal that there is a discrepancy in the shape of （112） peak. Samples annealed with ＂one step profile＂ have splits on （112） peaks, while samples annealed with ＂two step profile＂ have relatively symmetrical （112） peaks. Grazing incident X-ray diffraction and en- ergy dispersive spectrum measurements of samples successively etched in bromine methanol show that CuIn（S,Se）2 thin films have better in-depth composition uniformity after ＂two step profile＂ annealing. The reaction mechanism during the two thermal processing was also investigated by X-ray diffraction and Raman spectra.
基金supported by the National Natural Science Foundation of China(61874159,62074052,61974173,52072327,51702085 and 51802081)the Joint Talent Cultivation Funds of NSFC-HN(U1704151 and U1904192)+1 种基金the Zhongyuan Thousand Talents(Zhongyuan Scholars)Program of Henan Province(202101510004)the Science and Technology Innovation Talents in Universities of Henan Province(21HASTIT023)。
文摘The environmentally friendly Cu_(2)ZnSn(S,Se)_(4)(CZTSSe) compounds are promising direct bandgap materials for application in thin film solar cells, but the spontaneous surface defects disordering would lead to large open-circuit voltage deficit(V_(oc,deficit)) and significantly limit kesterite photovoltaics performance,primarily arising from the generated more recombination centers and insufficient p to n conversion at p-n junction. Herein, we establish a surface defects ordering structure in CZTSSe system via local substitution of Cu by Ag to suppress disordered Cu_(Zn) defects and generate benign n-type Zn_(Ag) donors. Taking advantage of the decreased annealing temperature of Ag F post deposition treatment(PDT), the high concentration of Ag incorporated into surface absorber facilitates the formation of surface ordered defect environment similar to that of efficient CIGS PV. The manipulation of highly doped surface structure could effectively reduce recombination centers, increase depletion region width and enlarge the band bending near p-n junction. As a result, the Ag F-PDT device finally achieves maximum efficiency of 12.34% with enhanced V_(oc) of 0.496 V. These results offer a new solution route in surface defects and energy-level engineering, and open the way to build up high quality p-n junction for future development of kesterite technology.
基金supported by the National Key R&D Program of China(2019YFB1503500,2018YFB1500200,2018YEE0203400)the Natural Science Foundation of China(U1902218,11774187)the 111 project(B16027)。
文摘It is very important to understand why a small amount of alkali metal doping in Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)solar cells can improve the conversion efficiency.In this work,Na-doped CZTSSe is prepared by a simple solution method,and then the effects on the surface properties of the absorber layer,the buffer layer growth,and the modifications of the solar cell performance induced by the Na doping are studied.The surface of the absorber layer is more Cu-depletion and less roughness due to the Na doping.In addition,the contact angle of the surface increases because of Na doping.As a consequence,the thickness of the CdS buffer layer is significantly reduced and the optical losses in the CdS buffer layer are decreased.The difference of quasi-Fermi levels(EFn-EFp) increases with a small amount of Na doping in the CZTSSe solar cell,so that open circuit voltage(VOC) increased significantly.This work offers new insights into the effects of Na doping on CZTSSe via a solution-based approach and provides a deeper understanding of the origin of the efficiency improvement of Na-doped CZTSSe thin film solar cells.
基金supported by the National Natural Science Foundation of China(51771072)the Outstanding Youth Scientist Foundation of Hunan Province(2020JJ2006)+2 种基金the Youth 1000 Talent Program of ChinaFundamental Research Funds for the Central UniversitiesHunan University State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body Independent Research Project(71860007)。
文摘The nanoporous Cu_(2-x)Se with Cu(Se-5%)surface catalysts were prepared through in situ dynamic restructuring strategy during the electrochemical process,which achieves highly selective electrochemical CO_(2) reduction to methanol.In situ and quasi-operando spectroscopic results provide a deep insight into the catalytic active centres of reconstructed heterogeneous catalysts for CO_(2) electroreduction.
文摘Thin films of copper indium gallium selenide Cu（In,Ga）Se2 （CIGS） were prepared by sequential elemental layer deposition in vacuum at room temperature. The as-deposited films were heated in vacuum for compound formation, and were studied at temperature as high as 1250℃ for the first time. These films were concurrently studied for their structural properties by X-ray diffraction （XRD） technique. The XRD analyses include phase transition studies, grain size variation and microstrain measurements with the reaction temperature and time.It has been observed that there are three distinct regions of variation in all these parameters. These regions belong to three temperature regimes： 〈450℃, 450-950℃, and 〉950℃. It is also seen that the compound formation starts at 250℃, with ternary phases appearing at 350℃ or above. Whereas, there is another phase shift at 950℃ without any preference to the quaternary compound.
基金supported by the National Natural Science Foundation of China(U2002216,52172261,51627803,51972332,22075150,and U1902218)the National Key Research and Development Program of China(2019YFE0118100)。
文摘Photo-generated carrier recombination loss at the CZTSSe/Cd S front interface is a key issue to the opencircuit voltage(V_(OC)) deficit of Cu_(2)ZnSnS_(x)Se_(4-x)(CZTSSe) solar cells. Here, by the aid of an easy-handling spin-coating method, a thin PCBM([6,6]-phenyl-C61-butyric acid methyl ester) layer as an electron extraction layer has been introduced on the top of CdS buffer layer to modify CZTSSe/CdS/ZnO-ITO(In_(2)O_(3):Sn) interfacial properties. Based on Sn^(4+)/DMSO(dimethyl sulfoxide) solution system, a totalarea efficiency of 12.87% with a VOC of 529 m V has been achieved. A comprehensive investigation on the influence of PCBM layer on carrier extraction, transportation and recombination processes has been carried out. It is found that the PCBM layer can smooth over the Cd S film roughness, thus beneficial for a dense and flat window layer. Furthermore, this CZTSSe/Cd S/PCBM heterostructure can accelerate carrier separation and extraction and block holes from the front interface as well, which is mainly ascribed to the downward band bending of the absorber and a widened space charge region. Our work provides a feasible way to improve the front interfacial property and the cell performance of CZTSSe solar cells by the aid of organic interfacial materials.
