Alkali metal doping or sulfurization are commonly applied in Cu_(2)ZnSnSe_(4) (CZTSe) solar cell to improve the open-circuit voltage (VOC). However, alkali metal sulfide affording both alkali metal and sulfur is seldo...Alkali metal doping or sulfurization are commonly applied in Cu_(2)ZnSnSe_(4) (CZTSe) solar cell to improve the open-circuit voltage (VOC). However, alkali metal sulfide affording both alkali metal and sulfur is seldom to be studied, which restrains the development of kesterite solar cells. In this study, we evaporate Li_(2)S during selenization process and hope to provide both alkali metal and sulfur to CZTSe film. The result indicates that Li shows a gradient distribution near the surface of CZTSe film and the content of S is slight. The film quality is improved and the recombination at grain boundaries is decreased after Li_(2)S treatment. Besides, the bandgap of the absorber gets wider. Under the synergy of sulfur and lithium (mainly from lithium), the work function of the treated absorber gets higher and the conduction band offset (CBO) is in the ideal range. Combined with these contributions, the V_(OC) of the champion device treated by Li_(2)S dramatically increase by 120 mV. This study discloses that alkali metal brings the main effect on the performance of the kesterite solar cell even an alkali metal sulfide is evaporated, which deepens the understanding of sulfurization of CZTSe and also promote the progress of kesterite solar cells.展开更多
High-voltage organic solar cells(OSCs)have received increasing attention because of their promising applications in tandem devices and indoor photovoltaics,but the trade-off between energy loss and charge generation i...High-voltage organic solar cells(OSCs)have received increasing attention because of their promising applications in tandem devices and indoor photovoltaics,but the trade-off between energy loss and charge generation induced by exciton binding energy(E_(b))has become one of the biggest bottlenecks limiting the development of this field.Here,a wide bandgap(WBG)nonfullerene acceptor BTA503 with reduced E_(b) is designed by changing the phenyl side chain on the central core of Cl-BTA5 to an alkyl chain.The diverseπ-πinteractions and enhanced molecular stacking of BTA503 are responsible for its reduced E_(b).Furthermore,both the diminished charge recombination and the fast exciton dissociation caused by the small E_(b) favor the generation of more charge carriers for the PTQ10:BTA503 combination.The efficient Forster resonance energy transfer(FRET)and multiple π-π stacking patterns provide additional charge transfer and transport pathways.Ultimately,the PTQ10:BTA503-based OSC device achieves a V_(OC)of 1.112 V and a PCE of 12.70%,which is higher than that of PTQ10:Cl-BTA5(PCE=10.92%).Simultaneously,the thick film(~300 nm)binary device of PTQ10:BTA503 achieves a PCE of 10.13% with a V_(OC)of 1.102 V,which is the best result for thick film high-voltage OSCs.More importantly,the ternary device of PTQ10:BTA503:Cl-BTA5(1:0.9:0.1)realizes a champion PCE of 13.12% with a V_(OC)of 1.126 V.Our study demonstrates that it is an effective strategy to reduce E_(b) of A_(2)-A_(1)-D-A_(1)-A_(2) type WBG acceptors by modulating the side chains on D unit,which further favors the corresponding devices to obtain world-record PCE and improves their potential for commercial applications.展开更多
The development of kesterite photovoltaic solar cells has been hindered by large open-circuit voltage(V_(oc))deficit.Recently,Snzn deep point defect and associative defect cluster have been recognized as the main culp...The development of kesterite photovoltaic solar cells has been hindered by large open-circuit voltage(V_(oc))deficit.Recently,Snzn deep point defect and associative defect cluster have been recognized as the main culprit for the Voc losses.Therefore,manipulating the deep-level donor of Snzn antisite defects is crucial for breaking through the bottleneck of present Cu_(2) ZnSn(S,Se)_(4)(CZTSSe)photovoltaic technology.In this study,the Snzn deep traps in CZTSSe absorber layer are suppressed by incorporation of Ge.The energy levels and concentration of Snzn defects measured by deep-level transient spectroscopy(DLTS)decrease significantly.In addition,the grain growth of CZTSSe films is also promoted due to Ge implantation,yielding the high quality absorber layer.Consequently,the efficiency of CZTSSe solar cells increases from 9.15%to 11.48%,largely attributed to the 41 mV Voc increment.展开更多
The passivation of non-radiative states and inhibition of band tailings are desirable for improving the open-circuit voltage(V_(oc))of CZTSSe thin-film solar cells.Recently,alkali metal doping has been investigated to...The passivation of non-radiative states and inhibition of band tailings are desirable for improving the open-circuit voltage(V_(oc))of CZTSSe thin-film solar cells.Recently,alkali metal doping has been investigated to passivate defects in CZTSSe films.Herein,we investigate Li doping effects by applying Li OH into CZTSSe precursor solutions,and verify that carrier transport is enhanced in the CZTSSe solar cells.Systematic characterizations demonstrate that Li doping can effectively passivate non-radiative recombination centers and reduce band tailings of the CZTSSe films,leading to the decrease in total defect density and the increase in separation distance between donor and acceptor.Fewer free carriers are trapped in the band tail states,which speeds up carrier transport and reduces the probability of deep-level defects capturing carriers.The charge recombination lifetime is about twice as long as that of the undoped CZTSSe device,implying the heterojunction interface recombination is also inhibited.Besides,Li doping can increase carrier concentration and enhance build-in voltage,leading to a better carrier collection.By adjusting the Li/(Li+Cu)ratio to 18%,the solar cell efficiency is increased significantly to 9.68%with the fill factor(FF)of 65.94%,which is the highest FF reported so far for the flexible CZTSSe solar cells.The increased efficiency is mainly attributed to the reduction of V_(oc)deficit and the improved CZTSSe/Cd S junction quality.These results open up a simple route to passivate non-radiative states and reduce the band tailings of the CZTSSe films and improve the efficiency of the flexible CZTSSe solar cells.展开更多
We proposed a novel Al Ga N/Ga N enhancement-mode（E-mode） high electron mobility transistor（HEMT） with a dual-gate structure and carried out the detailed numerical simulation of device operation using Silvaco Atla...We proposed a novel Al Ga N/Ga N enhancement-mode（E-mode） high electron mobility transistor（HEMT） with a dual-gate structure and carried out the detailed numerical simulation of device operation using Silvaco Atlas. The dual-gate device is based on a cascode connection of an E-mode and a D-mode gate. The simulation results show that electric field under the gate is decreased by more than 70% compared to that of the conventional E-mode MIS-HEMTs（from 2.83 MV/cm decreased to 0.83 MV/cm）. Thus, with the discussion of ionized trap density, the proposed dual-gate structure can highly improve electric field-related reliability, such as, threshold voltage stability. In addition, compared with HEMT with field plate structure, the proposed structure exhibits a simplified fabrication process and a more effective suppression of high electric field.展开更多
基金This work was supported by the National Key R&D Program of China(2018YFB1500200,2019YFB1503500)the National Natural Science Foundation of China(U1902218,11774187)the 111 Project(B16027).
文摘Alkali metal doping or sulfurization are commonly applied in Cu_(2)ZnSnSe_(4) (CZTSe) solar cell to improve the open-circuit voltage (VOC). However, alkali metal sulfide affording both alkali metal and sulfur is seldom to be studied, which restrains the development of kesterite solar cells. In this study, we evaporate Li_(2)S during selenization process and hope to provide both alkali metal and sulfur to CZTSe film. The result indicates that Li shows a gradient distribution near the surface of CZTSe film and the content of S is slight. The film quality is improved and the recombination at grain boundaries is decreased after Li_(2)S treatment. Besides, the bandgap of the absorber gets wider. Under the synergy of sulfur and lithium (mainly from lithium), the work function of the treated absorber gets higher and the conduction band offset (CBO) is in the ideal range. Combined with these contributions, the V_(OC) of the champion device treated by Li_(2)S dramatically increase by 120 mV. This study discloses that alkali metal brings the main effect on the performance of the kesterite solar cell even an alkali metal sulfide is evaporated, which deepens the understanding of sulfurization of CZTSe and also promote the progress of kesterite solar cells.
基金supported by the National Natural Science Foundation of China(21875052,51873044)。
文摘High-voltage organic solar cells(OSCs)have received increasing attention because of their promising applications in tandem devices and indoor photovoltaics,but the trade-off between energy loss and charge generation induced by exciton binding energy(E_(b))has become one of the biggest bottlenecks limiting the development of this field.Here,a wide bandgap(WBG)nonfullerene acceptor BTA503 with reduced E_(b) is designed by changing the phenyl side chain on the central core of Cl-BTA5 to an alkyl chain.The diverseπ-πinteractions and enhanced molecular stacking of BTA503 are responsible for its reduced E_(b).Furthermore,both the diminished charge recombination and the fast exciton dissociation caused by the small E_(b) favor the generation of more charge carriers for the PTQ10:BTA503 combination.The efficient Forster resonance energy transfer(FRET)and multiple π-π stacking patterns provide additional charge transfer and transport pathways.Ultimately,the PTQ10:BTA503-based OSC device achieves a V_(OC)of 1.112 V and a PCE of 12.70%,which is higher than that of PTQ10:Cl-BTA5(PCE=10.92%).Simultaneously,the thick film(~300 nm)binary device of PTQ10:BTA503 achieves a PCE of 10.13% with a V_(OC)of 1.102 V,which is the best result for thick film high-voltage OSCs.More importantly,the ternary device of PTQ10:BTA503:Cl-BTA5(1:0.9:0.1)realizes a champion PCE of 13.12% with a V_(OC)of 1.126 V.Our study demonstrates that it is an effective strategy to reduce E_(b) of A_(2)-A_(1)-D-A_(1)-A_(2) type WBG acceptors by modulating the side chains on D unit,which further favors the corresponding devices to obtain world-record PCE and improves their potential for commercial applications.
基金financially supported by the National Natural Science Foundation of China(U1904192,62074052,52072327,61974173,61874159 and 51802081)the Key Science and Technology Research Project of Education Department of Henan Province(19A140003)+1 种基金the Key Science and Technology Program of Henan Province(192102210001)Zhongyuan Thousand Talents(Zhongyuan Scholars)Program of Henan Province(202101510004)。
文摘The development of kesterite photovoltaic solar cells has been hindered by large open-circuit voltage(V_(oc))deficit.Recently,Snzn deep point defect and associative defect cluster have been recognized as the main culprit for the Voc losses.Therefore,manipulating the deep-level donor of Snzn antisite defects is crucial for breaking through the bottleneck of present Cu_(2) ZnSn(S,Se)_(4)(CZTSSe)photovoltaic technology.In this study,the Snzn deep traps in CZTSSe absorber layer are suppressed by incorporation of Ge.The energy levels and concentration of Snzn defects measured by deep-level transient spectroscopy(DLTS)decrease significantly.In addition,the grain growth of CZTSSe films is also promoted due to Ge implantation,yielding the high quality absorber layer.Consequently,the efficiency of CZTSSe solar cells increases from 9.15%to 11.48%,largely attributed to the 41 mV Voc increment.
基金supported by the National Natural Science Foundation of China(62074037,52002073)the Science and Technology Department of Fujian Province(2020I0006)+3 种基金the Natural Science Foundation of Fujian Province(2019J01218)the Fujian Science&Technology Innovation Laboratory for Optoelectronic Information of China(2021ZZ124)the Education and Scientific Research Project of Fujian Province(JAT200372)the Scientific Research Project of Fujian Jiangxia University(JXZ2019006)。
文摘The passivation of non-radiative states and inhibition of band tailings are desirable for improving the open-circuit voltage(V_(oc))of CZTSSe thin-film solar cells.Recently,alkali metal doping has been investigated to passivate defects in CZTSSe films.Herein,we investigate Li doping effects by applying Li OH into CZTSSe precursor solutions,and verify that carrier transport is enhanced in the CZTSSe solar cells.Systematic characterizations demonstrate that Li doping can effectively passivate non-radiative recombination centers and reduce band tailings of the CZTSSe films,leading to the decrease in total defect density and the increase in separation distance between donor and acceptor.Fewer free carriers are trapped in the band tail states,which speeds up carrier transport and reduces the probability of deep-level defects capturing carriers.The charge recombination lifetime is about twice as long as that of the undoped CZTSSe device,implying the heterojunction interface recombination is also inhibited.Besides,Li doping can increase carrier concentration and enhance build-in voltage,leading to a better carrier collection.By adjusting the Li/(Li+Cu)ratio to 18%,the solar cell efficiency is increased significantly to 9.68%with the fill factor(FF)of 65.94%,which is the highest FF reported so far for the flexible CZTSSe solar cells.The increased efficiency is mainly attributed to the reduction of V_(oc)deficit and the improved CZTSSe/Cd S junction quality.These results open up a simple route to passivate non-radiative states and reduce the band tailings of the CZTSSe films and improve the efficiency of the flexible CZTSSe solar cells.
基金supported by the Key Technologies Support Program of Jiangsu Province(No.BE2013002-2)the National Key Scientific Instrument and Equipment Development Projects of China(No.2013YQ470767)
文摘We proposed a novel Al Ga N/Ga N enhancement-mode（E-mode） high electron mobility transistor（HEMT） with a dual-gate structure and carried out the detailed numerical simulation of device operation using Silvaco Atlas. The dual-gate device is based on a cascode connection of an E-mode and a D-mode gate. The simulation results show that electric field under the gate is decreased by more than 70% compared to that of the conventional E-mode MIS-HEMTs（from 2.83 MV/cm decreased to 0.83 MV/cm）. Thus, with the discussion of ionized trap density, the proposed dual-gate structure can highly improve electric field-related reliability, such as, threshold voltage stability. In addition, compared with HEMT with field plate structure, the proposed structure exhibits a simplified fabrication process and a more effective suppression of high electric field.
