有机金属卤化物钙钛矿薄膜中的光诱导载流子动力学和动态带重整效应
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摘要
近年来有机-无机金属卤化物钙钛矿太阳能电池因具有光电能量转换效率高、制备工艺简单等优点,引起了学术界和产业界的广泛关注,其优异的光电特性逐渐在能源领域展现出独特的优越特性.在短短几年内,有机-无机混合物钙钛矿太阳能电池的能量转换效率已经高达23%,发展速度逐步赶上甚至超越了成熟的硅太阳能电池.本文利用飞秒瞬态吸收光谱,对二步法制备的(5-AVA)_(0.05)(MA)_(0.95)PbI_3和(5-AVA)_(0.05)(MA)_(0.95)PbI_3/Spiro-OMeTAD有机-无机卤化物钙钛矿薄膜材料的激发态动力学进行了对比研究,详细讨论了两种薄膜样品中的电荷载流子产生与复合机制.通过紫外-可见吸收光谱测得钙钛矿薄膜(5-AVA)_(0.05)(MA)_(0.95)PbI_3和(5-AVA)_(0.05)(MA)_(0.95)PbI_3/Spiro-OMeTAD的吸收光谱与CH_3NH_3PbI_3钙钛矿薄膜材料的双价带结构相对应.从瞬态吸收光谱中,观察到760 nm附近的光致漂白信号,此时的载流子复合过程符合二阶动力学过程,而在约550—700 nm光谱范围内则是光诱导激发态吸收信号.实验结果表明,(5-AVA)_(0.05)(MA)_(0.95)PbI_3钙钛矿薄膜样品中光生载流子主要的弛豫途径是自由电子和空穴的复合.抽运光激发样品使价带中的电子跃迁到导带,随着延迟时间的增加,电子和空穴复合,光谱发生红移现象.所观察到的带重整效应可以根据Moss-Burstein效应解释.相比较而言,(5-AVA)_(0.05)(MA)_(0.95)PbI_3/Spiro-OMeTAD钙钛矿薄膜样品在光激发后电子和空穴分离,空穴迅速转移到空穴传输层,这将导致样品吸收度增加,漂白信号快速恢复,电子-空穴的复合不再对漂白信号的弛豫动力学起主导作用,同时也削弱了带重整现象.本文的实验结果对半导体有机-无机金属卤化物钙钛矿薄膜在光伏领域的应用具有重要意义,为今后高效、稳定的钙钛矿太阳电池的研究提供了参考.
In recent years, the solution-processed organic-inorganic perovskite solar cells have attracted considerable attention because of their advantages of high energy conversion efficiency, low cost, and easily processing. Organometallic halide perovskite solar cells have gradually demonstrated particular superior properties in energy field due to their excellent photoelectric properties. This has been triggered by the unprecedented increase in its overall power conversion efficiency reaching 23% in just a few years, and it is becoming a direct competitor against the existing leading technology silicon. In this paper, 5-AVA-doped organometal halide perovskite films,(5-AVA)_(0.05)(MA)_(0.95)PbI_3and(5-AVA)_(0.05)(MA)_(0.95)PbI_3/Spiro-OMeTAD, are prepared by the two-step method. The generation and recombination mechanism of charge carriers in two kinds of film samples are discussed in detail. The bivalent band structure of perovskite film material CH_3NH_3PbI_3 is determined by ultraviolet-visible absorption spectra of perovskite film(5-AVA)_(0.05)(MA)_(0.95)PbI_3and(5-AVA)_(0.05)(MA)_(0.95)PbI_3/Spiro-OMeTAD. We investigate the photocarrier dynamics and band filling effects in these two organometal halide perovskite films by using femtosecond transient absorption spectroscopy. For(5-AVA)_(0.05)(MA)_(0.95)PbI_3, the photoinduced bleach recovery at 760 nm reveals that band-edge recombination follows second-order kinetics, indicating that the dominant relaxation pathway is via the recombination of free electrons and holes. With regard to the perovskite film(5-AVA)_(0.05)(MA)_(0.95)PbI_3and(5-AVA)_(0.05)(MA)_(0.95)PbI_3/SpiroOMeTAD, the signal is photoinduced absorption from 550 nm to 700 nm. As the delay time increases, the electrons and holes are recombined, which results in a red shift of absorption spectrum in(5-AVA)_(0.05)(MA)_(0.95)PbI_3. This can be referred to as Moss-Burstein band filling model. In contrast, the electrons and holes of(5-AVA)_(0.05)(MA)_(0.95)PbI_3/SpiroOMeTAD perovskite film sample are separated after photoexcitation. The holes rapidly transfer to the hole transport layer of Spiro-OMeTAD. It will lead to an increase in sample absorbance and a rapid recovery of bleaching signals.Consequently, electron-hole recombination is no longer a dominant pathway to the relaxation of photocarriers and the band filling effect is not significant in the composite film. Our findings provide a valuable insight into the understanding of the charge carrier dynamics and spectral band filling in mixed perovskites. These results conduce to the understanding of the intrinsic photo-physics of semiconducting organometal halide perovskites with direct implications for photovoltaic and optoelectronic applications, and provide a reference for the future research of perovskite solar cells.
In recent years, the solution-processed organic-inorganic perovskite solar cells have attracted considerable attention because of their advantages of high energy conversion efficiency, low cost, and easily processing. Organometallic halide perovskite solar cells have gradually demonstrated particular superior properties in energy field due to their excellent photoelectric properties. This has been triggered by the unprecedented increase in its overall power conversion efficiency reaching 23% in just a few years, and it is becoming a direct competitor against the existing leading technology silicon. In this paper, 5-AVA-doped organometal halide perovskite films,(5-AVA)_(0.05)(MA)_(0.95)PbI_3and(5-AVA)_(0.05)(MA)_(0.95)PbI_3/Spiro-OMeTAD, are prepared by the two-step method. The generation and recombination mechanism of charge carriers in two kinds of film samples are discussed in detail. The bivalent band structure of perovskite film material CH_3NH_3PbI_3 is determined by ultraviolet-visible absorption spectra of perovskite film(5-AVA)_(0.05)(MA)_(0.95)PbI_3and(5-AVA)_(0.05)(MA)_(0.95)PbI_3/Spiro-OMeTAD. We investigate the photocarrier dynamics and band filling effects in these two organometal halide perovskite films by using femtosecond transient absorption spectroscopy. For(5-AVA)_(0.05)(MA)_(0.95)PbI_3, the photoinduced bleach recovery at 760 nm reveals that band-edge recombination follows second-order kinetics, indicating that the dominant relaxation pathway is via the recombination of free electrons and holes. With regard to the perovskite film(5-AVA)_(0.05)(MA)_(0.95)PbI_3and(5-AVA)_(0.05)(MA)_(0.95)PbI_3/SpiroOMeTAD, the signal is photoinduced absorption from 550 nm to 700 nm. As the delay time increases, the electrons and holes are recombined, which results in a red shift of absorption spectrum in(5-AVA)_(0.05)(MA)_(0.95)PbI_3. This can be referred to as Moss-Burstein band filling model. In contrast, the electrons and holes of(5-AVA)_(0.05)(MA)_(0.95)PbI_3/SpiroOMeTAD perovskite film sample are separated after photoexcitation. The holes rapidly transfer to the hole transport layer of Spiro-OMeTAD. It will lead to an increase in sample absorbance and a rapid recovery of bleaching signals.Consequently, electron-hole recombination is no longer a dominant pathway to the relaxation of photocarriers and the band filling effect is not significant in the composite film. Our findings provide a valuable insight into the understanding of the charge carrier dynamics and spectral band filling in mixed perovskites. These results conduce to the understanding of the intrinsic photo-physics of semiconducting organometal halide perovskites with direct implications for photovoltaic and optoelectronic applications, and provide a reference for the future research of perovskite solar cells.
引文
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[3]Manser J S,Christians J A,Kamat P V 2016 Chem.Rev.116 12956
[4]Etgar L,Gao P,Xue Z,Peng Q,Chandiran A K,Liu B,Nazeeruddin M K,Gratzel M 2012 J.Am.Chem.Soc.134 17396
[5]Saliba M,Matsui T,Seo J Y,Domanski K,CorreaBaena J P,Nazeeruddin M K,Zakeerudding S M,Tress W,Abate A,Hagfeldt A,Gratzel M 2016 Energy Environ.Sci.9 1989
[6]Singh S P,Nagarjuna P 2014 Dalton Trans.43 5247
[7]Xiao M,Huang F,Huang W,Dkhissi Y,Zhu Y,Etheridge J,Gray-Weale A,Bach U,Cheng Y B,Spiccia L 2014 Angew.Chem.Int.Ed.126 1
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[9]Chen H,Pan X,Liu W,Cai M,Kou D,Huo Z,Fang X,Dai S 2013 Chem.Commun.49 7277
[10]Lv S,Han L,Xiao J,Zhu L,Shi J,Wei H,Xu Y,Dong J,Xu X,Li D,Wang S,Luo Y,Meng Q,Li X 2014 Chem.Commun.50 6931
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[13]Zhou H P,Chen Q,Li G,Luo S,Song T B,Duan H S,Hong Z R,You J B,Liu Y S,Yang Y 2014 Science 345542
[14]Yamada Y,Nakamura T,Endo M,Wakamiya A,Kanemitsu Y 2014 J.Am.Chem.Soc.136 11610
[15]Deschler F,Price M,Pathak S,Klintberg L E,Jarausch D D,Higler R,Huttner S,Leijtens T,Stranks S D,Snaith H J,Atature M,Phillips R T,Friend R H 2014J.Phys.Chem.Lett.5 1421
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[17]Saba M,Cadelano M,Marongiu D,Chen F,Sarritzu V,Sestu N,Figus C,Aresti M,Piras R,Lehmann A G,Cannas C,Musinu A,Quochi F,Mura A,Bongiovanni G 2014 Nature Commun.5 5049
[18]Manser J S,Kamat P V 2014 Nature Photon.8 737
[19]Marchioro A,Teuscher J,Friedrich D,Kunst M,van de Krol R,Moehl T,Gratzel M,Moser J E 2014 Nature Photon.8 250
[20]Wu X,Trinh M T,Niesner D,Zhu H,Norman Z,Owen J S,Yaffe O,Kudisch B J,Zhu X Y 2015 J.Am.Chem.Soc.137 2089
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[22]Yan H J,An B L,Fan Z F,Zhu X Y,Lin X,Jin Z M,Ma G H 2016 Appl.Phys.A 122 414
[23]Xing G,Mathews N,Sun S,Lim S S,Lam Y M,Gratzel M,Mhaisalkar S,Sum T C 2013 Science 342 344
[24]Guo Z,Wan Y,Yang M,Jordan S,Zhu K,Huang L 2017Science 356 6333
[25]Mei A,Li X,Liu L,Ku Z,Liu T,Rong Y,Xu M,Hu M,Chen J,Yang Y,Gratzel M,Han H 2014 Science 345295
[26]Ghanassi M,Schanne-Klein M C,Hache F,Ekimov A I,Ricard D,Flytzanis C 1993 Appl.Phys.Lett.62 78
[27]Burstein E 1954 Phys.Rev.93 632
[28]Moss T S 1954 Proc.Phys.Soc.B 67 775
[29]Kamat P V,Dimitrijevic N M,Nozik A J 1989 J.Phys.Chem.93 2873
[30]Kawamura K,Maekawa K,Yanagi H,Hirano M,Hosono H 2003 Thin Solid Films 445 182
[31]Hickey S G,Riley D J,Tull E J 2000 J.Phys.Chem.B104 7623
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[33]Giorgi G,Fujisawa J,Segawa H,Yamashita K 2013 J.Phys.Chem.Lett.4 4213