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In the classical planar heterojunction perovskite solar cells (PSCs), the electron conducting TiO2 layer shows lower conductivity than the hole transporting materials such as spiro-OMeTAD, which becomes one of the key problems in improving the power conversion efficiency (PCE) of PSCs. In this study, the surface of compact TiO2 layer is modified by a thin self-assembled dodecanedioic acid (DDDA) molecular layer. The TiO2 substrates are immersed into the DDDA solution for 0.5, 2.5, 4.5, 22 h, respectively. It is found that the PCE of PSCs is improved when using the DDDA modified TiO2, showing optimized PCE of 15.35%0.75% under AM 1.5G illumination at 100 mWcm-2 after 4.5 h modification. The short current density (JSC) of the best device is improved from 20.34 mA cm-2 to 23.28 mA cm-2, with the PCE increasing from 14.17% to 15.92%. And it is found that the hysteresis of the PSC is also reduced remarkably with hysteresis index decreasing from 0.4288 to 0.2430. In the meantime, the device with DDDA modification shows a significant improvement in light stability, keeping 71% of its initial PCE value after 720 min exposure under AM 1.5G illumination at 100 mW cm-2 without encapsulation. As a contrast, the device without DDDA modification keeps 59% of its initial PCE value under the same condition. To reveal the mechanism, we investigate the surface energy level change using ultraviolet photoemission spectroscopy. It is found that after DDDA modification, the valence-band maximum energy (EVBM) of TiO2 decreases from -7.25 eV to -7.32 eV, and the conduction-band minimum energy (ECBM) of TiO2 from -4.05 eV to -4.12 eV. The shifting of energy level optimizes the energy level alignment at the interface between the TiO2 and perovskite. It promotes the transport of electrons from perovskite layer to compact TiO2 layer and obstructs the transport of holes from perovskite layer to compact TiO2 layer more effectively. In addition, the decrease of ECBM implies the increase of conductivity of TiO2. We further design a series of electrical experiments, and confirm that the modification improves the conductivity of TiO2 obviously with both contact resistance and thin-film resistance decreasing. In summary, our results indicate the enormous potential of the compact TiO2 layer with a thin self-assembled DDDA molecular layer modification to construct efficient and stable planar heterojunction PSCs for practical applications.
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Keywords:
- perovskite material /
- solar cells /
- planar heterojunction /
- electron transport
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[7] Yang W S, Noh J H, Jeon N J, Kim Y C, Ryu S, Seo J, Seok S I 2015 Science 348 1234
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[9] Yang W S, Park B W, Jung E H, Jeon N J, Kim Y C, Lee D U, Shin S S, Seo J, Kim E K, Noh J H, Seok S I 2017 Science 356 1376
[10] Li Y W, Zhao Y, Chen Q, Yang Y, Liu Y S, Hong Z R, Liu Z H, Hsieh Y T, Meng L, Li Y F, Yang Y 2015 J. Am. Chem. Soc. 137 15540
[11] Wang F Z, Tan Z A, Dai S Y, Li Y F 2015 Acta Phys. Sin. 64 038401 (in Chinese) [王福芝, 谭占鳌, 戴松元, 李永舫 2015 物理学报 64 038401]
[12] Stranks S D, Eperon G E, Grancini G, Menelaou C, Alcocer M J P, Leijtens T, Herz L M, Petrozza A, Snaith H J 2013 Science 342 341
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[37] Lao C S, Li Y, Wong C P, Wang Z L 2007 Nano Lett. 7 1323
[38] Xu L, Tang C Q, Qian J 2010 Acta Phys. Sin. 59 2721 (in Chinese) [徐凌, 唐超群, 钱俊 2010 物理学报 59 2721]
[39] Park N G 2013 J. Phys. Chem. Lett. 4 2423
[40] Snaith H J, Abate A, Ball J M, Eperon G E, Leijtens T, Noel N K, Stranks S D, Wang J T, Wojciechowski K, Zhang W 2014 J. Phys. Chem. Lett. 5 1511
[41] Yella A, Heiniger L P, Gao P, Nazeeruddin M K, Grtzel M 2014 Nano Lett. 14 2591
[42] Jeon N J, Noh J H, Kim Y C, Yang W S, Ryu S, Seok S I 2014 Nat. Mater. 13 897
[43] Dualeh A, Moehl T, Tetreault N, Teuscher J, Gao P, Nazeeruddin M K, Grtzel M 2014 ACS Nano 8 362
[44] Mei A Y, Li X, Liu L F, Ku Z L, Liu T F, Rong Y G, Xu M, Hu M, Chen J Z, Yang Y, Grtzel M, Han H W 2014 Science 345 295
[45] Bai Y B, Wang Q Y, L R T, Zhu H W, Kang F Y 2016 Chin. Sci. Bull. 61 489 (in Chinese) [白宇冰, 王秋莹, 吕瑞涛, 朱宏伟, 康飞宇 2016 科学通报 61 489]
[46] Ito S, Tanaka S, Manabe K, Nishino H 2014 J. Phys. Chem. C 118 16995
[47] Fujishima A, Rao T N, Tryk D A 2000 J. Photochem. Photobiol. C 1 1
[48] Leijtens T, Eperon G E, Pathak S, Abate A, Lee M M, Snaith H J 2013 Nat. Commun. 4 2885
[49] Guo X D, Niu G D, Wang L D 2015 Acta Chim. Sin. 73 211 (in Chinese) [郭旭东, 牛广达, 王立铎 2015 化学学报 73 211]
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[1] Kojima A, Teshima K, Shirai Y, Miyasaka T J 2009 Am. Chem. Soc. 131 6050
[2] Lee M M, Teuscher J, Miyasaka T, Murakami T N, Snaith H J 2012 Science 338 643
[3] Kim H S, Lee C R, Im J H, Lee K B, Moehl T, Marchioro A, Moon S J, Humphry-Baker R, Yum J H, Moser J E, Grtzel M, Park N G 2012 Sci. Rep. 2 591
[4] Liu M Z, Johnston M B, Snaith H J 2013 Nature 501 395
[5] Lee J W, Seol D J, Cho A N, Park N G 2014 Adv. Mater. 26 4991
[6] 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 345 542
[7] Yang W S, Noh J H, Jeon N J, Kim Y C, Ryu S, Seo J, Seok S I 2015 Science 348 1234
[8] Saliba M, Matsui T, Domanski K, Seo J Y, Ummadisingu A, Zakeeruddin S M, Correa-Baena J P, Tress W R, Abate A, Hagfeldt A, Grtzel M 2016 Science 354 206
[9] Yang W S, Park B W, Jung E H, Jeon N J, Kim Y C, Lee D U, Shin S S, Seo J, Kim E K, Noh J H, Seok S I 2017 Science 356 1376
[10] Li Y W, Zhao Y, Chen Q, Yang Y, Liu Y S, Hong Z R, Liu Z H, Hsieh Y T, Meng L, Li Y F, Yang Y 2015 J. Am. Chem. Soc. 137 15540
[11] Wang F Z, Tan Z A, Dai S Y, Li Y F 2015 Acta Phys. Sin. 64 038401 (in Chinese) [王福芝, 谭占鳌, 戴松元, 李永舫 2015 物理学报 64 038401]
[12] Stranks S D, Eperon G E, Grancini G, Menelaou C, Alcocer M J P, Leijtens T, Herz L M, Petrozza A, Snaith H J 2013 Science 342 341
[13] Zhao Y X, Nardes A M, Zhu K 2014 J. Phys. Chem. Lett. 5 490
[14] Xing G C, Mathews N, Sun S, Lim S S, Lam Y M, Grtzel M, Mhaisalkar S, Sum T C 2013 Science 342 344
[15] Yao X, Ding Y L, Zhang X D, Zhao Y 2015 Acta Phys. Sin. 64 038805 (in Chinese) [姚鑫, 丁艳丽, 张晓丹, 赵颖 2015 物理学报 64 038805]
[16] Song Z H, Wang S R, Xiao Y, Li X G 2015 Acta Phys. Sin. 64 033301 (in Chinese) [宋志浩, 王世荣, 肖殷, 李祥高 2015 物理学报 64 033301]
[17] Liu P, Yang B C, Liu G, Wu R S, Zhang C J, Wan F, Li Y G, Yang J L, Gao Y L, Zhou C H 2017 Chin. Phys. B 26 058401
[18] Shi J J, Xu X, Li D M, Meng Q B 2015 Small 11 2472
[19] Kumar M H, Yantara N, Dharani S, Graetzel M, Mhaisalkar S, Boix P P, Mathews N 2013 Chem. Commun. 49 11089
[20] Zhang Q F, Dandeneau C S, Zhou X Y, Cao G Z 2009 Adv. Mater. 21 4087
[21] Ariyanto N P, Abdullah H, Syarif J, Yuliarto B, Shaari S 2010 Funct. Mater. Lett. 3 303
[22] Goncalves A S, Ges M S, Fabregat-Santiago F, Moehl T, Davolos M R, Bisquert J, Yanagida S, Nogueira A F, Bueno P R 2011 Electrochim. Acta 56 6503
[23] Liu Y, Xu Z, Zhao S L, Qiao B, Li Y, Qin Z L, Zhu Y Q 2017 Acta Phys. Sin. 66 118801 (in Chinese) [刘毅, 徐征, 赵谡玲, 乔泊, 李杨, 秦梓伦, 朱友勤 2017 物理学报 66 118801]
[24] Ding X J, Ni L, Ma S B, Ma Y Z, Xiao L X, Chen Z J 2015 Acta Phys. Sin. 64 038802 (in Chinese) [丁雄傑, 倪露, 马圣博, 马英壮, 肖立新, 陈志坚 2015 物理学报 64 038802]
[25] Wojciechowski K, Saliba M, Leijtens T, Abate A, Snaith H J 2014 Energy Environ. Sci. 7 1142
[26] Hendry E, Koeberg M, O'Regan B, Bonn M 2006 Nano Lett. 6 755
[27] Savenije T J, Huijser A, Vermeulen M J W, Katoh R 2008 Chem. Phys. Lett. 461 93
[28] Fravventura M C, Deligiannis D, Schins J M, Siebbeles L D A, Savenije T J 2013 J. Phys. Chem. C 117 8032
[29] Chen J Q, Yang D H, Jiang J H, Ma A B, Song D, Ni C Y, Hu M Z 2015 Mater Rev.: Rev. 29 1 (in Chinese) [陈建清, 杨东辉, 江静华, 马爱斌, 宋丹, Ni Chaoying, Hu Michael Z 2015 材料导报: 综述篇 29 1]
[30] Abate A, Leijtens T, Pathak S, Teuscher J, Avolio R, Errico M E, Kirkpatrik J, Ball J M, Docampo P, McPherson I, Snaith H J 2013 Phys. Chem. Chem. Phys. 15 2572
[31] Poplavskyy D, Nelson J 2003 J. Appl. Phys. 93 341
[32] Abrusci A, Stranks S D, Docampo P, Yip H L, Jen A K Y, Snaith H J 2013 Nano Lett. 13 3124
[33] Wojciechowski K, Stranks S D, Abate A, Sadoughi G, Sadhanala A, Kopidakis N, Rumbles G, Li C Z, Friend R H, Jen A K Y, Snaith H J 2014 ACS Nano 8 12701
[34] Wang J X, Bi Z N, Liang Z R, Xu X Q 2016 Acta Phys. Sin. 65 058801 (in Chinese) [王军霞, 毕卓能, 梁柱荣, 徐雪青 2016 物理学报 65 058801]
[35] Burschka J, Pellet N, Moon S J, Baker R H, Gao P, Nazeeruddin M K, Grtzel M 2013 Nature 499 316
[36] Cojocaru L, Uchida S, Sanehira Y, Nakazaki J, Kubo T, Segawa H 2015 Chem. Lett. 44 674
[37] Lao C S, Li Y, Wong C P, Wang Z L 2007 Nano Lett. 7 1323
[38] Xu L, Tang C Q, Qian J 2010 Acta Phys. Sin. 59 2721 (in Chinese) [徐凌, 唐超群, 钱俊 2010 物理学报 59 2721]
[39] Park N G 2013 J. Phys. Chem. Lett. 4 2423
[40] Snaith H J, Abate A, Ball J M, Eperon G E, Leijtens T, Noel N K, Stranks S D, Wang J T, Wojciechowski K, Zhang W 2014 J. Phys. Chem. Lett. 5 1511
[41] Yella A, Heiniger L P, Gao P, Nazeeruddin M K, Grtzel M 2014 Nano Lett. 14 2591
[42] Jeon N J, Noh J H, Kim Y C, Yang W S, Ryu S, Seok S I 2014 Nat. Mater. 13 897
[43] Dualeh A, Moehl T, Tetreault N, Teuscher J, Gao P, Nazeeruddin M K, Grtzel M 2014 ACS Nano 8 362
[44] Mei A Y, Li X, Liu L F, Ku Z L, Liu T F, Rong Y G, Xu M, Hu M, Chen J Z, Yang Y, Grtzel M, Han H W 2014 Science 345 295
[45] Bai Y B, Wang Q Y, L R T, Zhu H W, Kang F Y 2016 Chin. Sci. Bull. 61 489 (in Chinese) [白宇冰, 王秋莹, 吕瑞涛, 朱宏伟, 康飞宇 2016 科学通报 61 489]
[46] Ito S, Tanaka S, Manabe K, Nishino H 2014 J. Phys. Chem. C 118 16995
[47] Fujishima A, Rao T N, Tryk D A 2000 J. Photochem. Photobiol. C 1 1
[48] Leijtens T, Eperon G E, Pathak S, Abate A, Lee M M, Snaith H J 2013 Nat. Commun. 4 2885
[49] Guo X D, Niu G D, Wang L D 2015 Acta Chim. Sin. 73 211 (in Chinese) [郭旭东, 牛广达, 王立铎 2015 化学学报 73 211]
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