F8BT薄膜表面形貌及与Al形成界面的电子结构和反应

潘宵; 鞠焕鑫; 冯雪飞; 范其瑭; 王嘉兴; 杨耀文; 朱俊发

doi:10.7498/aps.64.077304

摘要

基于共轭聚合物光电器件的性能与聚合物的表面形貌、分子取向、以及与金属电极形成的界面结构密切相关. 本文利用原子力显微镜(AFM)、同步辐射光电子能谱(SRPES)和近边X射线吸收精细结构谱(NEXAFS)等, 研究了聚(9, 9-二辛基芴并苯噻二唑)(F8BT)薄膜的表面形貌、分子取向及其与Al 电极形成界面过程的结构变化. 结果表明, 在略低于F8BT玻璃转变温度(Tg=130 ℃)条件下对F8BT薄膜进行退火, 可明显增加薄膜的表面粗糙度, 薄膜中F8BT 的分子取向角约为49, 9, 9-二辛基芴单元(F8)与苯噻唑单元(BT)几乎在同一平面. 在Al/F8BT 界面形成过程中, Al与F8BT中的C, N和S均发生不同程度的化学反应, 并导致价带结构和未占据分子轨道(LUMO)态密度的变化. Al对F8BT进行n型掺杂引起F8BT能带弯曲的同时, 未占据能级被部分占据, 更多的电子将被注入到LUMO+1中. 通过考察价带电子结构、芯能级位移及二次截止边的变化, 绘制了清晰的Al/F8BT界面能级图.

关键词:

Abstract

The surface morphology and molecular orientation of -conjugated polymers, along with the chemical interaction and electronic structure at the interface between metals and these polymers, strongly affect the performance of the polymer-based organic electronic and optoelectronic devices. In this study, atomic force microscopy (AFM), synchrotron radiation photoemission spectroscopy (SRPES), and near edge X-ray absorption fine structure (NEXAFS) have been used to in situ investigate the morphology, structure, and molecular orientation of spin-coated poly(9,9-dioctylfluorene-co-benzothiodiazole) (F8BT) films and their interaction with the vapor-deposited Al metal. F8BT films were prepared by spin-coating the F8BT chloroform solution onto clean gold-coated silicon wafer surfaces. The room temperature spin-coated F8BT film is rather flat, while mild annealing treatments (120 ℃) below the glass transition temperature (Tg=130 ℃) lead to an apparent increase of surface roughness of F8BT film, which is helpful to effectively increase the contact areas between metals and F8BT. After 70 ℃ annealing in vacuum, the aromatic rings of F8BT preferentially stand more edge-on, making an average tilt angle of approximately 49 with the substrate, while the 9,9-dioctylfluorene unit (F8) and the benzothiodiazole unit (BT) nearly lie in the same plane. Upon vapor-depositing Al metal onto F8BT at room temperature, strong chemical interactions occur between Al and F8BT, as evidenced by the distinct changes of the S 2p, N 1s and C 1s spectra. Al reacts with S atoms more strongly than with N and C atoms in F8BT. In addition, obvious structural changes in valence band of F8BT are also observed during the Al deposition. Furthermore, Al dopes electrons into F8BT, leading to downward band bending, formation of interfacial dipole at the Al/F8BT interface, and partial occupation of lowest unoccupied molecular orbits (LUMO). However, no doping-induced gap states can be observed during the formation of Al/F8BT interface. Through the investigation of the core-level and valence band spectra evolution of F8BT together with the shifts of secondary electron cutoff during Al deposition, an energy level alignment diagram at the Al/F8BT interface is derived. The information gained through this study will help better understand the correlation between the interface structures of metal electrodes on semiconducting, -conjugated polymer materials and the performances of real polymer-based electronic and optoelectronic devices, which will in turn help develop the more efficient polymer-based organic devices.

Keywords:

F8BT /
surface morphology /
synchrotron radiation photoelectron spectroscopy /
near edge X-ray absorption fine structure

作者及机构信息

1.
中国科学技术大学国家同步辐射实验室, 合肥 230029;

2.
台湾同步辐射研究中心, 新竹 30076

基金项目: 国家自然科学基金面上项目(批准号: 21173200, 21473178)和国家重点基础研究发展计划(批准号: 2013CB834605)资助的课题.

Authors and contacts

1.
National Synchrotron Radiation Labratory, University of Science and Technology of China, Hefei 230029, China;

2.
National Synchrotron Radiation Research Centre of Taiwan, Hsinchu 30076, China

Funds: Project supported by the National Natural Science Foundation of China (Grant Nos. 21173200, 21473178), and the National Key Basic Research Program of China (Grant No. 2013CB834605).

参考文献

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[2]	Forrest S R 2004 Nature 428 911
[3]	Bolink H J, Coronado E, Repetto D, Sessolo M, Barea E M, Bisquert J, Garcia-Belmonte G, Prochazka J, Kavan L 2008 Adv. Funct. Mater. 18 145
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[8]	Nam S, Shin M, Kim H, Ha C S, Ree M, Kim Y 2011 Adv. Funct. Mater. 21 4527
[9]	Cataldo S, Sartorio C, Giannazzo F, Scandurra A, Pignataro B 2014 Nanoscale 6 3566
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[11]	Orimo A, Masuda K, Honda S, Benten H, Ito S, Ohkita H, Tsuji H 2010 Appl. Phys. Lett. 96
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[18]	Fung M K, Lai S L, Bao S N, Lee C S, Lee S T, Wu W W, Inbasekaran M, O’Brien J J 2002 J. Vac. Sci. Technol. A 20 911
[19]	Zhou Y H, Zhu L P, Qiu Y 2011 Org. Electron. 12 234
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[21]	Zhao W, Guo Y X, Feng X F, Zhang L, Zhang W H, Zhu J F 2009 Chinese Sci. Bull. 54 1978
[22]	Ju H X, Feng X F, Ye Y F, Zhang L, Pan H B, Campbell C T, Zhu J F 2012 J. Phys. Chem. C 116 20465
[23]	Ju H X, Ye Y F, Feng X F, Pan H B, Zhu J F, Ruzycki N, Campbell C T 2014 J. Phys. Chem. C 118 6352
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[25]	Liao L S, Cheng L F, Fung M K, Lee C S, Lee S T, Inbasekaran M, Woo E P, Wu W W 2000 Phys. Rev. B 62 10004
[26]	Liao L S, Fung M K, Cheng L F, Lee C S, Lee S T, Inbasekaran M, Woo E P, Wu W W 2000 Appl. Phys. Lett. 77 3191
[27]	Fung M K, Lai S L, Tong S W, Bao S N, Lee C S, Wu W W, Inbasekaran M, O’Brien J J, Lee S T 2003 J. Appl. Phys. 94 5763
[28]	Fung M K, Tong S W, Lai S L, Bao S N, Lee C S, Wu W W, Inbasekaran M, O’Brien J J, Liu S Y, Lee S T 2003 J. Appl. Phys. 94 2686
[29]	Feng X F, Zhao W, Ju H X, Zhang L, Ye Y F, Zhang W H, Zhu J F 2012 Org. Electron. 13 1060
[30]	Min H, Girard-Lauriault P L, Gross T, Lippitz A, Dietrich P, Unger W E S 2012 Anal. Bioanal. Chem. 403 613
[31]	Shin M, Kim H, Kim Y 2011 Mater. Sci. Eng. B-Adv. 176 382
[32]	Xiong Y, Peng J B, Wu H B, Wang J 2009 Chin. Phys.Lett. 26 097801
[33]	Yan H P, Swaraj S, Wang C, Hwang I, Greenham N C, Groves C, Ade H, McNeill C R 2010 Adv. Funct. Mater. 20 4329
[34]	Meier R, Chiang H Y, Ruderer M A, Guo S A, Korstgens V, Perlich J, Muller B P 2012 J. Polym. Sci. Pol. Phys. 50 631
[35]	Lee T W, Park O O 2000 Adv. Mater. 12 801
[36]	Anselmo A S, Dzwilewski A, Svensson K, Moons E 2013 J. Polym. Sci. Pol. Phys. 51 176
[37]	Watts B, Schuettfort T, McNeill C R 2011 Adv. Funct. Mater. 21 1122
[38]	Gliboff M, Sulas D, Nordlund D, deQuilettes D W, Nguyen P D, Seidler G T, Li X S, Ginger D S 2014 J. Phys. Chem. C 118 5570
[39]	Salaneck W R, Bredas J L 1996 Adv. Mater. 8 48
[40]	Bebin P, Prud’homme R E 2003 Chem. Mater. 15 965
[41]	Oultache A K, Prud’homme R E 2000 Polym. Advan. Technol. 11 316
[42]	Michaelson H B 1977 J. Appl. Phys. 48 4729

施引文献

[1]	Brabec C J 2004 Sol. Energ. Mat. Sol. C 83 273
[2]	Forrest S R 2004 Nature 428 911
[3]	Bolink H J, Coronado E, Repetto D, Sessolo M, Barea E M, Bisquert J, Garcia-Belmonte G, Prochazka J, Kavan L 2008 Adv. Funct. Mater. 18 145
[4]	Haque S A, Koops S, Tokmoldin N, Durrant J R, Huang J S, Bradley D D C, Palomares E 2007 Adv. Mater. 19 683
[5]	Kabra D, Song M H, Wenger B, Friend R H, Snaith H J 2008 Adv. Mater. 20 3447
[6]	Nakayama Y, Morii K, Suzuki Y, Machida H, Kera S, Ueno N, Kitagawa H, Noguchi Y, Ishii H 2009 Adv. Funct. Mater. 19 3746
[7]	Duhm S, Heimel G, Salzmann I, Glowatzki H, Johnson R L, Vollmer A, Rabe J P, Koch N 2008 Nat. Mater. 7 326
[8]	Nam S, Shin M, Kim H, Ha C S, Ree M, Kim Y 2011 Adv. Funct. Mater. 21 4527
[9]	Cataldo S, Sartorio C, Giannazzo F, Scandurra A, Pignataro B 2014 Nanoscale 6 3566
[10]	Meier R, Chiang H Y, Ruderer M A, Guo S A, Korstgens V, Perlich J, Muller-Buschbaum P 2012 J. Polym. Sci. Pol. Phys. 50 631
[11]	Orimo A, Masuda K, Honda S, Benten H, Ito S, Ohkita H, Tsuji H 2010 Appl. Phys. Lett. 96
[12]	Roige A, Campoy-Quiles M, Osso J O, Alonso M I, Vega L F, Garriga M 2012 Synthetic Met. 161 2570
[13]	Ma W L, Yang C Y, Gong X, Lee K, Heeger A J 2005 Adv. Funct. Mater. 15 1617
[14]	Donley C L, Zaumseil J, Andreasen J W, Nielsen M M, Sirringhaus H, Friend R H, Kim J S 2005 J. Am Chem. Soc. 127 12890
[15]	Hofmann O T, Egger D A, Zojer E 2010 Nano. Lett. 10 4369
[16]	Crispin X, Geskin V, Crispin A, Cornil J, Lazzaroni R, Salaneck W R, Bredas J L 2002 J. Am. Chem. Soc. 124 8131
[17]	Frisch J, Glowatzki H, Janietz S, Koch N 2009 Org. Electron. 10 1459
[18]	Fung M K, Lai S L, Bao S N, Lee C S, Lee S T, Wu W W, Inbasekaran M, O’Brien J J 2002 J. Vac. Sci. Technol. A 20 911
[19]	Zhou Y H, Zhu L P, Qiu Y 2011 Org. Electron. 12 234
[20]	Dannetun P, Boman M, Stafstrom S, Salaneck W R, Lazzaroni R, Fredriksson C, Bredas J L, Zamboni R, Taliani C 1993 J. Chem. Phys. 99 664
[21]	Zhao W, Guo Y X, Feng X F, Zhang L, Zhang W H, Zhu J F 2009 Chinese Sci. Bull. 54 1978
[22]	Ju H X, Feng X F, Ye Y F, Zhang L, Pan H B, Campbell C T, Zhu J F 2012 J. Phys. Chem. C 116 20465
[23]	Ju H X, Ye Y F, Feng X F, Pan H B, Zhu J F, Ruzycki N, Campbell C T 2014 J. Phys. Chem. C 118 6352
[24]	Greczynski G, Fahlman M, Salaneck W R 2000 J. Chem. Phys. 113 2407
[25]	Liao L S, Cheng L F, Fung M K, Lee C S, Lee S T, Inbasekaran M, Woo E P, Wu W W 2000 Phys. Rev. B 62 10004
[26]	Liao L S, Fung M K, Cheng L F, Lee C S, Lee S T, Inbasekaran M, Woo E P, Wu W W 2000 Appl. Phys. Lett. 77 3191
[27]	Fung M K, Lai S L, Tong S W, Bao S N, Lee C S, Wu W W, Inbasekaran M, O’Brien J J, Lee S T 2003 J. Appl. Phys. 94 5763
[28]	Fung M K, Tong S W, Lai S L, Bao S N, Lee C S, Wu W W, Inbasekaran M, O’Brien J J, Liu S Y, Lee S T 2003 J. Appl. Phys. 94 2686
[29]	Feng X F, Zhao W, Ju H X, Zhang L, Ye Y F, Zhang W H, Zhu J F 2012 Org. Electron. 13 1060
[30]	Min H, Girard-Lauriault P L, Gross T, Lippitz A, Dietrich P, Unger W E S 2012 Anal. Bioanal. Chem. 403 613
[31]	Shin M, Kim H, Kim Y 2011 Mater. Sci. Eng. B-Adv. 176 382
[32]	Xiong Y, Peng J B, Wu H B, Wang J 2009 Chin. Phys.Lett. 26 097801
[33]	Yan H P, Swaraj S, Wang C, Hwang I, Greenham N C, Groves C, Ade H, McNeill C R 2010 Adv. Funct. Mater. 20 4329
[34]	Meier R, Chiang H Y, Ruderer M A, Guo S A, Korstgens V, Perlich J, Muller B P 2012 J. Polym. Sci. Pol. Phys. 50 631
[35]	Lee T W, Park O O 2000 Adv. Mater. 12 801
[36]	Anselmo A S, Dzwilewski A, Svensson K, Moons E 2013 J. Polym. Sci. Pol. Phys. 51 176
[37]	Watts B, Schuettfort T, McNeill C R 2011 Adv. Funct. Mater. 21 1122
[38]	Gliboff M, Sulas D, Nordlund D, deQuilettes D W, Nguyen P D, Seidler G T, Li X S, Ginger D S 2014 J. Phys. Chem. C 118 5570
[39]	Salaneck W R, Bredas J L 1996 Adv. Mater. 8 48
[40]	Bebin P, Prud’homme R E 2003 Chem. Mater. 15 965
[41]	Oultache A K, Prud’homme R E 2000 Polym. Advan. Technol. 11 316
[42]	Michaelson H B 1977 J. Appl. Phys. 48 4729

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