CdSeS合金结构量子点的多激子俄歇复合过程
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摘要
多激子效应通常是指吸收单个光子产生多个激子的过程,该效应不仅可以为研究基于量子点的太阳能电池开拓新思路,还可以为提高太阳能电池的光电转换效率提供新方法.但是,超快多激子产生和复合机制尚不明确.这里以CdSeS合金结构量子点为研究对象,研究了其多激子生成和复合动力学.稳态吸收光谱显示, 510, 468和430 nm附近的稳态吸收峰,分别对应1S_(3/2)(h)-1S(e)(或1S), 2S_(3/2)(h)-1S(e)(或2S)和1P_P(3/2)(h)-1P(e)(或1P)激子的吸收带.通过飞秒时间分辨瞬态吸收光谱和纳秒时间分辨荧光光谱两种时间分辨光谱技术对CdSeS合金结构量子点的超快动力学进行了探究,结果显示, 1S激子的双激子复合时间大概是80 ps,这一时间比传统量子点的双激子复合时间(小于50 ps)延长了近一倍,结合最近发展的超快界面电荷分离技术,在激子湮灭之前将其利用起来,这一时间的延长将有很大的应用前景;其中,在2S和1P激子中除上述双激子复合外,还存在一个通过声子耦合路径的空穴弛豫过程,时间大概是5—6 ps.最后,利用纳秒时间分辨荧光光谱得到该样品体系单激子复合的时间约为200 ns.
Multiexciton generation is a process where multiple excitons are generated by absorbing single photons.Efficient multiexciton generation in quantum dots may be a revolutionary discovery, because it provides a new method to improve the solar-to-electric power conversion efficiency in quantum dots-based solar cells and to design novel quantum dots-based multielectron or hole photocatalysts. However, the mechanism of ultrafast multiexciton generation and recombination remain unclear. In this paper, alloy-structured quantum dots,CdSeS, are prepared by the hot injection method. The generation and recombination mechanism of charge carriers in quantum dots samples are discussed in detail. The bivalent band structure of alloy-structured quantum dots is determined by ultraviolet-visible absorption spectra. It is found that the 1 S_(3/2)(h)-1 S(e)(or 1 S),2 S_(3/2)(h)-1 S(e)(or 2 S) and 1 P_(3/2)(h)-1 P(e)(or 1 P) exciton absorption bands of these quantum dots are at 510 nm, 468 nm and 430 nm, respectively. Femtosecond transient absorption spectroscopy and nanosecond timeresolved photoluminescence spectroscopy are used to investigate the ultrafast exciton generation and recombination dynamics in the alloy-structured quantum dots. By fitting the transient kinetics of 1 S exciton bleach, an average biexciton decay time is obtained to be about 80 ps, which is almost twice the decay time of traditional quantum dots(less than 50 ps). Combined with the recently developed ultrafast interface charge separation technology that can extract multiple excitons before their annihilation, it will have a promising application prospect. Moreover, there is a hole relaxation on a the time scale of 5-6 ps via a phonon coupling pathway to lower-energy hole states in addition to the above-described ultrafast exciton-exciton annihilation process in 2 S and 1 P excitons. Furthermore, by nanosecond time-resolved photoluminescence spectroscopy, it can be concluded that the charge separated state is long-lived(200 ns). Our findings provide a valuable insight into the understanding of ultrafast multiexciton generation and recombination in quantum dots. These results are helpful to understand the intrinsic photo-physics of multiexciton generation in quantum dots, to implement the photovoltaic and optoelectronic applications, and to ascertain the exciton relaxation dynamics of quantum dots.
Multiexciton generation is a process where multiple excitons are generated by absorbing single photons.Efficient multiexciton generation in quantum dots may be a revolutionary discovery, because it provides a new method to improve the solar-to-electric power conversion efficiency in quantum dots-based solar cells and to design novel quantum dots-based multielectron or hole photocatalysts. However, the mechanism of ultrafast multiexciton generation and recombination remain unclear. In this paper, alloy-structured quantum dots,CdSeS, are prepared by the hot injection method. The generation and recombination mechanism of charge carriers in quantum dots samples are discussed in detail. The bivalent band structure of alloy-structured quantum dots is determined by ultraviolet-visible absorption spectra. It is found that the 1 S_(3/2)(h)-1 S(e)(or 1 S),2 S_(3/2)(h)-1 S(e)(or 2 S) and 1 P_(3/2)(h)-1 P(e)(or 1 P) exciton absorption bands of these quantum dots are at 510 nm, 468 nm and 430 nm, respectively. Femtosecond transient absorption spectroscopy and nanosecond timeresolved photoluminescence spectroscopy are used to investigate the ultrafast exciton generation and recombination dynamics in the alloy-structured quantum dots. By fitting the transient kinetics of 1 S exciton bleach, an average biexciton decay time is obtained to be about 80 ps, which is almost twice the decay time of traditional quantum dots(less than 50 ps). Combined with the recently developed ultrafast interface charge separation technology that can extract multiple excitons before their annihilation, it will have a promising application prospect. Moreover, there is a hole relaxation on a the time scale of 5-6 ps via a phonon coupling pathway to lower-energy hole states in addition to the above-described ultrafast exciton-exciton annihilation process in 2 S and 1 P excitons. Furthermore, by nanosecond time-resolved photoluminescence spectroscopy, it can be concluded that the charge separated state is long-lived(200 ns). Our findings provide a valuable insight into the understanding of ultrafast multiexciton generation and recombination in quantum dots. These results are helpful to understand the intrinsic photo-physics of multiexciton generation in quantum dots, to implement the photovoltaic and optoelectronic applications, and to ascertain the exciton relaxation dynamics of quantum dots.
引文
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[37]Liu C,Peterson J J,Krauss T D 2014 J.Phys.Chem.Lett.53032
[2]Werner J H,Kolodinski S,Queisser H J 1994 Phys.Rev.Lett.72 3851
[3]Beard M C,Luther J M,Nozik A J 2014 Nat.Nanotechnol.9951
[4]ten Cate S,Sandeep C S S,Liu Y,Law M,Kinge S,Houtepen A J,Schins J M,Siebbeles L D A 2015 Acc.Chem.Res.48 174
[5]Tahara H,Sakamoto M,Teranishi T,Kanemitsu Y 2017Phys.Rev.Lett.119 247401
[6]Tahara H,Sakamoto M,Teranishi T,Kanemitsu Y 2018 Nat.Commun.9 3179
[7]Damtie F A,Karki K J,Pullerits T,Wacker A 2016 J.Chem.Phys.145 064703
[8]Park Y S,Guo S J,Makarov N S,Klimov V I 2015 ACSNano 9 10386
[9]Hu F R,Yin C Y,Zhang H C,Sun C,Yu W W,Zhang C F,Wang X Y,Zhang Y,Xiao M 2016 Nano Lett.16 6425
[10]Hu F R,Zhang H C,Sun C,Yin C Y,LüB H,Zhang C F,Yu W W,Wang X Y,Zhang Y,Xiao M 2015 ACS Nano 912410
[11]Zhao G,Cai Q B,Liu X T,Li P W,Zhang Y Q,Shao G S,Liang C 2019 IEEE J.Photovolt.9 194
[12]Chen Z H,Zhang Z L,Yang J F,Chen W J,Teh Z L,Wang D,Yuan L,Zhang J B,Stride J A,Conibeer G J,Patterson R J,Huang S J 2018 J.Mater.Chem.C 6 9861
[13]Lin Q L,Yun H J,Liu W Y,Song H J,Makarov N S,Isaienko O,Nakotte T,Chen G,Luo H M,Klimov V I,Pietryga J M 2017 J.Am.Chem.Soc.139 6644
[14]Zhang Z L,Chen Z H,Yuan L,Chen W J,Yang J F,Wang B,Wen X M,Zhang J B,Hu L,Stride J A,Conibeer G J,Patterson R J,Huang S J 2017 Adv.Mater.29 1703214
[15]Li Q Y,Xu Z H,McBride J R,Lian T Q 2017 ACS Nano 112545
[16]Debnath T,Maity P,Maiti S,Ghosh H N 2014 J.Phys.Chem.Lett.5 2836
[17]Spencer A P,Peters W K,Neale N R,Jonas D M 2019 J.Phys.Chem.C 123 848
[18]Al-Ghamdi M S,Sayari A,Sfaxi L 2016 J.Alloys Compd.685202
[19]Kwak G Y,Kim T G,Hong S,Kim A,Ha M H,Kim K J2018 Sol.Energy 164 89
[20]Zhang P F,Feng Y,Wen X M,Cao W K,Anthony R,Kortshagen U,Conibeer G,Huang S J 2016 Sol.Energ.Mat.Sol.C 145 391
[21]Kryjevski A,Mihaylov D,Kilina S,Kilin D 2017 J.Chem.Phys.147 154106
[22]Amori A R,Hou Z T,Krauss T D 2018 Annu.Rev.Phys.Chem.69 81
[23]Schaller R D,Sykora M,Pietryga J M,Klimov V I 2006 Nano Lett.6 424
[24]Ghimire S,Biju V 2018 J.Photoch.Photobio.C 34 137
[25]Zhu H,Lian T 2012 J.Am.Chem.Soc.134 11289
[26]Shi X F,Xia X Y,Cui G W,Deng N,Zhao Y Q,Zhuo L H,Tang B 2015 Appl.Catal.B.Environ.163 123
[27]Schaller R D,Agranovich V M,Klimov V I 2005 Nat.Phys.1189
[28]Gordi M,Moravvej-Farshi M K,Ramezani H 2018Chemphyschem 19 2782
[29]Jier H,Zhuangqun H,Ye Y,Haiming Z,Tianquan L 2010 J.Am.Chem.Soc.132 4858
[30]Pijpers J J H,Milder M T W,Delerue C,Bonn M 2010 J.Phys.Chem.C 114 6318
[31]Yang Y,Lian T Q 2014 Coordin.Chem.Rev.263 229
[32]Ghosh H N,Singhal P,Maity P,Jha S K 2017 Chemistry 2310590
[33]Kroupa D M,Pach G F,Voros M,Giberti F,Chernomordik B D,Crisp R W,Nozik A J,Johnson J C,Singh R,Klimov VI,Galli G,Beard M C 2018 ACS Nano 12 10084
[34]Harris R D,Homan S B,Kodaimati M,He C,Nepomnyashchii A B,Swenson N K,Lian S C,Calzada R,Weiss E A 2016 Chem.Rev.116 12865
[35]Klimov V I 2007 Annu.Rev.Phys.Chem.58 635
[36]Han Y C,Bao T 2015 Acta Phys.Sin.64 113021(in Chinese)[韩元春,包特木耳巴根2015物理学报64 113021]
[37]Liu C,Peterson J J,Krauss T D 2014 J.Phys.Chem.Lett.53032