科技的日新月異使得全球用電量自工業革命以來需求大增，傳統發電是採用燃煤火力發電，而燃煤的生成物為造成全球溫室效應的元兇，太陽能電池為目前較乾淨的能源，而本實驗所研究的甲基胺基碘化鉛(methylammonium lead iodide , MAPbI3)被視為最有潛力的太陽能電池材料，具有製備簡單且成本低的優勢，且目前的光電轉換效率為22%，而單晶的理論光電轉換效率可達到25%以上，但是其穩定性對於使用上及商業化有致命的缺點，空氣中的水氣及氧氣都會使材料裂解崩壞，光照則會加速劣化。本實驗採用探針掃描技術中的Quantitative nanomechanical (QNM)模式搭配及X光繞射探討MAPbI3的劣化機制，得知MAPbI3在水解劣化時彈性模數有三階段的變化，第一階段為彈性模數的上升，此上升的原因可能為MAPbI3晶粒成長造成，第二階段為彈性模數的下降，下降原因推測為MAPbI3逐漸裂解為PbI2，而此時的PbI2的結構較為鬆散，故而彈性模數下降，第三階段則判斷PbI2在水氣的幫助下使其結構緻密化先形成針狀結構，而後才出現六角形結構，由於結構的緻密化使得此階段彈性模數呈現上升趨勢。另外，在照光也會對MAPbI3裂解產生作用，在劣化初期無關環境的因素彈性模數都會有上升的情況，推測前期的晶粒成長無須在水氣的幫助下即可完成，而後MAPbI3開始裂解為結構鬆散的PbI2使得彈性模數的下降，此為第二階段的劣化，若是環境中具有水氣的存在則會有第三階段彈性模數的上升，此階段與水解劣化第三階段相同，為水氣幫助PbI2緻密化造成。另外，觀察單晶結構的水解裂解中發現(100)面較於(112)面具有較強的抗水性，但在光裂解時(100)面的光裂解速率較快，藉由AFM中的KPFM模式發現，在照光時(100)激發較多的電子，而光裂解的反應主要是氧氣和激發的電子形成自由基並且與MAPbI3反應造成劣化。經由以上結果評估，單晶之(100)面相較於(112)面更適合製作光電元件。

The Organic-inorganic perovskite material (MAPbI3) is the high potential material for the photoelectric application, but it is unstable under moisture and oxygen atmosphere. In this study, we try to establish the degradation mechanism of MAPbI3 and distinguish different kinds of phases formed during degradation by atomic force microscopy. The hydrolysis degradation of the MAPbI3 thin film can be divided into three stages. Otherwise, the photodegradation only has two stages; but if the environment contained high moisture, the third stage would appear. Different planes of material usually have different properties, and the (100) plane of MAPbI3 exhibited stronger moisture resistance than the (112) did, but the rate of photodegradation in (100) is faster than that in (112). As a result, the (100) plane of the MAPbI3 single crystal has more potential for the photoelectric device.
Keywords: perovskite, degradation, elastic modulus, atomic force microscopy

[1] Andrea Pisoni, Jaćim Jaćimović, Osor S. Barišić, Massimo Spina, Richard Gaál, László Forró, and Endre Horváth., "Ultra-Low Thermal Conductivity in Organic-Inorganic Hybrid Perovskite CH3NH3PbI3," J Phys Chem Lett, vol. 5, no. 14, pp. 2488-92, Jul 17 2014.
[2] H. Kawano, "Effective work functions for ionic and electronic emissions from mono- and polycrystalline surfaces," Progress in Surface Science, vol. 83, no. 1-2, pp. 1-165, 2008.
[3] Makhsud I. Saidaminov, Ahmed L. Abdelhady, Banavoth Murali, Erkki Alarousu, Victor M. Burlakov, Wei Peng, Ibrahim Dursun, Lingfei Wang, Yao He, Giacomo Maculan, Alain Goriely, Tom Wu, Omar F. Mohammed & Osman M. Bakr, "High-quality bulk hybrid perovskite single crystals within minutes by inverse temperature crystallization," Nat Commun, vol. 6, p. 7586, Jul 06 2015.
[4] Akihiro Kojima, Kenjiro Teshima, Yasuo Shirai, and Tsutomu Miyasaka, "Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells," J. AM. CHEM. SOC., vol. 131, pp. 6050–6051, 2009.
[5] T. Oku, "Crystal Structures of CH3NH3PbI3 and Related Perovskite Compounds Used for Solar Cells," in Solar Cells - New Approaches and Reviews, 2015.
[6] Woon Seok Yang, Byung-Wook Park, Eui Hyuk Jung, Nam Joong Jeon, Young Chan Kim, Dong Uk Lee, Seong Sik Shin, Jangwon Seo, Eun Kyu Kim, Jun Hong Noh, Sang Il Seok, "Iodide management in formamidinium-lead-halide–based perovskite layers for efficient solar cells," Science, vol. 356, no. 6345, pp. 1376-1379, 2017.
[7] Qiang Guo, Cong Li, Wenyuan Qiao, Shuang Ma, Fuzhi Wang, Bing Zhang, Linhua Hu, Songyuan Dai and Zhan’ao Tan, "The growth of a CH3NH3PbI3 thin film using simplified close space sublimation for efficient and large dimensional perovskite solar cells," Energy & Environmental Science, vol. 9, no. 4, pp. 1486-1494, 2016.
[8] Ping Fan, Di Gu, Guang-Xing Liang, Jing-Ting Luo, Ju-Long Chen, Zhuang-Hao Zheng, Dong-Ping Zhang, "High-performance perovskite CH3NH3PbI3 thin films for solar cells prepared by single-source physical vapour deposition," Sci Rep, vol. 6, p. 29910, Jul 18 2016.
[9] Qi Chen, Huanping Zhou, Ziruo Hong, Song Luo, Hsin-Sheng Duan, Hsin-Hua Wang, Yongsheng Liu, Gang Li, and Yang Yang, "Planar heterojunction perovskite solar cells via vapor-assisted solution process," J Am Chem Soc, vol. 136, no. 2, pp. 622-5, Jan 15 2014.
[10] V. A. Dong Shi, Riccardo Comin, Mingjian Yuan, Erkki Alarousu, Andrei Buin, Yin Chen, Sjoerd Hoogland, Alexander Rothenberger, Khabiboulakh Katsiev, Yaroslav Losovyj, Xin Zhang, Peter A. Dowben, Omar F. Mohammed, Edward H. Sargent, Osman M. Bakr, "Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals.," Science, vol. 347, no. 6221, pp. 519-522, 2015
[11] Qingfeng Dong, Yanjun Fang, Yuchuan Shao, Padhraic Mulligan, Jie Qiu, Lei Cao, Jinsong Huang, "Electron-hole diffusion lengths > 175 mm in solution-grown CH3NH3PbI3 single crystals," Science, vol. 347, no. 6225, pp. 967-970, 2015.
[12] Yangyang Dang, Yang Liu, Youxuan Sun, Dongsheng Yuan, Xiaolong Liu, Weiqun Lu, Guangfeng Liu, Haibing Xia and Xutang Tao, "Bulk crystal growth of hybrid perovskite material CH3NH3PbI3," CrystEngComm, vol. 17, no. 3, pp. 665-670, 2015.
[13] Jinsong Huang, Yuchuan Shao, and Qingfeng Dong, "Organometal Trihalide Perovskite Single Crystals: A Next Wave of Materials for 25% Efficiency Photovoltaics and Applications Beyond?," The Journal of Physical Chemistry Letters, vol. 6, no. 16, pp. 3218-3227, 2015.
[14] Makhsud I. Saidaminov, Ahmed L. Abdelhady, Giacomo Maculan, Osman M. Bakra, "Retrograde solubility of formamidinium and methylammonium lead halide perovskites enabling rapid single crystal growth," Chem Commun (Camb), vol. 51, no. 100, pp. 17658-61, Dec 28 2015.
[15] Yucheng Liu, Zhou Yang, Dong Cui, Xiaodong Ren, Jiankun Sun, Xiaojing Liu, Jingru Zhang, Qingbo Wei, Haibo Fan, Fengyang Yu, Xu Zhang, Changming Zhao, Shengzhong (Frank) Liu, "Two-Inch-Sized Perovskite CH3 NH3 PbX3 (X = Cl, Br, I) Crystals: Growth and Characterization," Adv Mater, vol. 27, no. 35, pp. 5176-83, Sep 16 2015.
[16] Yucheng Liu, Yunxia Zhang, Zhou Yang, Dong Yang, Xiaodong Ren, Liuqing Pang, Shengzhong (Frank) Liu, "Thinness- and Shape-Controlled Growth for Ultrathin Single-Crystalline Perovskite Wafers for Mass Production of Superior Photoelectronic Devices," Adv Mater, vol. 28, no. 41, pp. 9204-9209, Nov 2016.
[17] Zhipeng Lian, Qingfeng Yan, Qianrui Lv, Ying Wang, Lili Liu, Lijing Zhang, Shilie Pan, Qiang Li, Liduo Wang, Jia-Lin Sun, "High-Performance Planar-Type Photodetector on (100) Facet of MAPbI3 Single Crystal," Sci Rep, vol. 5, p. 16563, Nov 13 2015.
[18] Jianxu Ding, Ying Zhao, Songjie Du, Yingshuang Sun, Hongzhi Cui, Xiaoyuan Zhan, Xiaohua Cheng, and Lin Jing, "Controlled growth of MAPbBr3 single crystal: understanding the growth morphologies of vicinal hillocks on (100) facet to form perfect cubes," Journal of Materials Science, vol. 52, no. 13, pp. 7907-7916, 2017.
[19] Kai-Hung Wang, Liang-Chen Li, Muthaiah Shellaiah, Kien Wen Sun, "Structural and Photophysical Properties of Methylammonium Lead Tribromide (MAPbBr3) Single Crystals," Sci Rep, vol. 7, no. 1, p. 13643, Oct 20 2017.
[20] Yuxi Tian, Maximilian Peter, Eva Unger, Mohamed Abdellah, Kaibo Zheng, To˜nu Pullerits, Arkady Yartsev, Villy Sundstro¨m and Ivan G. Scheblykin, "Mechanistic insights into perovskite photoluminescence enhancement: light curing with oxygen can boost yield thousandfold," Phys Chem Chem Phys, vol. 17, no. 38, pp. 24978-87, Oct 14 2015.
[21] Conor Rocks, Vladimir Svrcek, Paul Maguirea, Davide Mariotti, "Understanding surface chemistry during MAPbI3 spray deposition and its effect on photovoltaic performance," Journal of Materials Chemistry C, vol. 5, no. 4, pp. 902-916, 2017.
[22] Aurélien M. A. Leguy, Yinghong Hu, Mariano Campoy-Quiles, M. Isabel Alonso, Oliver J. Weber, Pooya Azarhoosh, Mark van Schilfgaarde, Mark T. Weller, Thomas Bein, Jenny Nelson, Pablo Docampo, Piers R. F. Barnes, "Reversible Hydration of CH3NH3PbI3 in Films, Single Crystals, and Solar Cells," Chemistry of Materials, vol. 27, no. 9, pp. 3397-3407, 2015.
[23] Masaki Shirayama, Masato Kato, Tetsuhiko Miyadera, Takeshi Sugita, Takemasa Fujiseki, Shota Hara, Hideyuki Kadowaki, Daisuke Murata, Masayuki Chikamatsu, Hiroyuki Fujiwara, "Degradation mechanism of CH3NH3PbI3 perovskite materials upon exposure to humid air," Journal of Applied Physics, vol. 119, no. 11, 2016.
[24] Qianrui Lv, Wenhui He, Zhipeng Lian, Jie Ding, Qiang Li, Qingfeng Yan, "Anisotropic moisture erosion of CH3NH3PbI3single crystals," CrystEngComm, vol. 19, no. 6, pp. 901-904, 2017.
[25] Massimo Spina, Ayat Karimi, Wanda Andreoni, Carlo A. Pignedoli, Balint Nafradi, Laszlo Forro, and Endre Horvath, "Mechanical signatures of degradation of the photovoltaic perovskite CH3NH3PbI3 upon water vapor exposure," Applied Physics Letters, vol. 110, no. 12, 2017.
[26] Daniel Bryant, Nicholas Aristidou, Sebastian Pont, Irene Sanchez-Molina, Thana Chotchunangatchaval, Scot Wheeler, James R. Durrantab and Saif A. Haque, "Light and oxygen induced degradation limits the operational stability of methylammonium lead triiodide perovskite solar cells," Energy & Environmental Science, vol. 9, no. 5, pp. 1655-1660, 2016.
[27] Youzhen Li, Xuemei Xu, Congcong Wang, Ben Ecker, Junliang Yang, Jinsong Huang, Yongli Gao, "Light-Induced Degradation of CH3NH3PbI3 Hybrid Perovskite Thin Film," The Journal of Physical Chemistry C, vol. 121, no. 7, pp. 3904-3910, 2017.
[28] Lyubov A. Frolova, Nadezhda N. Dremova, Pavel A. Trosh, "The chemical origin of the p-type and n-type doping effects in the hybrid methylammonium-lead iodide (MAPbI3) perovskite solar cells," Chem Commun (Camb), vol. 51, no. 80, pp. 14917-20, Oct 14 2015.
[29] Xing Zhao, Nam-Gyu Park , "Stability Issues on Perovskite Solar Cells," Photonics, vol. 2, no. 4, pp. 1139-1151, 2015.
[30] Nam-Gyu Park, "Perovskite solar cells: an emerging photovoltaic technology," Materials Today, vol. 18, no. 2, pp. 65-72, 2015.
[31] Yixin Zhao, Alexandre M. Nardes, Kai Zhu, "Mesoporous perovskite solar cells: material composition, charge-carrier dynamics, and device characteristics," Faraday Discussions, vol. 176, pp. 301-312, 2014.
[32] Jiang-Jun Li, Jing-Yuan Ma, Qian-Qing Ge, Jin-Song Hu, Dong Wang, Li-Jun Wan, "Microscopic Investigation of Grain Boundaries in Organolead Halide Perovskite Solar Cells," ACS Appl Mater Interfaces, vol. 7, no. 51, pp. 28518-23, Dec 30 2015.
[33] G. Binnig, C. F. Quate, and C. Gerber, "Atomic force microscope," Phys Rev Lett, vol. 56, no. 9, pp. 930-933, Mar 3 1986.
[34] Ing-Shouh Hwang, "掃描探針顯微技術的原理及應用 Scanning Probe Microscopy: Principles and Applications," 科儀新知, vol. 第二十六卷第四期, pp. 7-17, 2005.
[35] Paul. West. Peter Eaton, "Atomic Force Microscopy," 2010.
[36] Sanghyun Paek, Nara Cho, Hyeju Choi, Hanbin Jeong, Jin Sung Lim, Jun-Yeon Hwang, Jae Kwan Lee, Jaejung Ko, "Improved External Quantum Efficiency from Solution-Processed (CH3NH3)PbI3 Perovskite/PC71BM Planar Heterojunction for High Efficiency Hybrid Solar Cells," The Journal of Physical Chemistry C, vol. 118, no. 45, pp. 25899-25905, 2014.
[37] Joel Troughton, Katherine Hooper, Trystan M. Watson, "Humidity resistant fabrication of CH3NH3PbI3 perovskite solar cells and modules," Nano Energy, vol. 39, pp. 60-68, 2017.
[38] Sigalit Aharon, Alexander Dymshits, Amit Rotem, Lioz Etgar, "Temperature dependence of hole conductor free formamidinium lead iodide perovskite based solar cells," Journal of Materials Chemistry A, vol. 3, no. 17, pp. 9171-9178, 2015.
[39] Tom Baikie, Yanan Fang, Jeannette M. Kadro, Martin Schreyer, Fengxia Wei, Subodh G. Mhaisalkar, Michael Graetzel and Tim J. White, "Synthesis and crystal chemistry of the hybrid perovskite (CH3NH3)PbI3 for solid-state sensitised solar cell applications," Journal of Materials Chemistry A, vol. 1, no. 18, 2013.
[40] Yang Zhou, Lu You, Shiwei Wang, Zhiliang Ku, Hongjin Fan, Daniel Schmidt, Andrivo Rusydi, Lei Chang, Le Wang, Peng Ren, Liufang Chen, Guoliang Yuan, Lang Chen, Junling Wang, "Giant photostriction in organic-inorganic lead halide perovskites," Nat Commun, vol. 7, p. 11193, Apr 5 2016.
[41] S. Sun, Y. Fang, G. Kieslich, T. J. White, and A. K. Cheetham, "Mechanical properties of organic–inorganic halide perovskites, CH3NH3PbX3 (X = I, Br and Cl), by nanoindentation," Journal of Materials Chemistry A, vol. 3, no. 36, pp. 18450-18455, 2015.
[42] W. Veiga, C.M. Lepienski, "Nanomechanical properties of lead iodide (PbI2) layered crystals," Materials Science and Engineering: A, vol. 335, no. 1–2, pp. 6-13, 25 September 2002.
[43] Jingbi You, Yang (Michael) Yang, Ziruo Hong, Tze-Bin Song, Lei Meng, Yongsheng Liu, Chengyang Jiang, Huanping Zhou, Wei-Hsuan Chang, Gang Li, Yang Yang, "Moisture assisted perovskite film growth for high performance solar cells," Applied Physics Letters, vol. 105, no. 18, 2014.
[44] Zhuan Zhu, Viktor G. Hadjiev, Yaoguang Rong, Rui Guo, Bo Cao, Zhongjia Tang, Fan Qin, Yang Li, Yanan Wang, Fang Hao, Swaminathan Venkatesan, Wenzhi Li, Steven Baldelli, Arnold M. Guloy, Hui Fang, Yandi Hu, Yan Yao, Zhiming Wang, and Jiming Bao, "Interaction of Organic Cation with Water Molecule in Perovskite MAPbI3: From Dynamic Orientational Disorder to Hydrogen Bonding," Chemistry of Materials, vol. 28, no. 20, pp. 7385-7393, 2016.
[45] Bert Conings, Jeroen Drijkoningen, Nicolas Gauquelin, Aslihan Babayigit, Jan D’Haen, Lien D’Olieslaeger, Anitha Ethirajan, Jo Verbeeck, Jean Manca, Edoardo Mosconi, Filippo De Angelis, Hans-Gerd Boyen, "Intrinsic Thermal Instability of Methylammonium Lead Trihalide Perovskite," Advanced Energy Materials, vol. 5, no. 15, 2015.
[46] Jinli Yang, Braden D. Siempelkamp, Dianyi Liu, Timothy L. Kelly, "Investigation of CH3NH3PbI3 Degradation Rates and Mechanisms in Controlled Humidity Environments Using in Situ Techniques," ACS Nano, vol. 9, 2015.
[47] Wei-Ting Wang, Sandeep K. Das, and Yian Tai, "Fully Ambient-Processed Perovskite Film for Perovskite Solar Cells: Effect of Solvent Polarity on Lead Iodide," ACS Appl Mater Interfaces, vol. 9, no. 12, pp. 10743-10751, Mar 29 2017.
[48] D. S. Bhavsar, K. B. Saraf, T. Seth, "Studies on Growth and Microstructure of Lead Iodide.", Cryst. Res. Technol., vol 37 2002
[49] R. Ahuja, H. Arwin, A. Ferreira da Silva, C. Persson, J. M. Osorio-Guillén, "Electronic and optical properties of lead iodide," Journal of Applied Physics, vol. 92, no. 12, pp. 7219-7224, 2002.
[50] Y. Rakita, S. R. Cohen, N. K. Kedem, G. Hodes, and D. Cahen, "Mechanical properties of APbX3 (A = Cs or CH3NH3; X = I or Br) perovskite single crystals," MRS Communications, vol. 5, no. 04, pp. 623-629, 2015.
[51] A. Tho̸gersen, J. H. Selj, and E. S. Marstein, "Oxidation Effects on Graded Porous Silicon Anti-Reflection Coatings," Journal of The Electrochemical Society, vol. 159, no. 5, 2012.
[52] Rongbin Wang, Chen Wu, Yun Hu, Jitao Li, Pengfei Shen, Qi Wang, Liangsheng Liao, Lijia Liu, Steffen Duhm, "CH3NH3PbI3-xClx under Different Fabrication Strategies: Electronic Structures and Energy-Level Alignment with an Organic Hole Transport Material," ACS Appl Mater Interfaces, vol. 9, no. 8, pp. 7859-7865, Mar 1 2017.
[53] O. A. Williams, "Nanocrystalline diamond," Diamond and Related Materials, vol. 20, no. 5-6, pp. 621-640, 2011.
[54] Hyoung Seop Kim, Mark B. Bush, "The effects of grain size and porosity on the elastic modulus of nanocrystalline materials," NanoStructured Materials, vol. 11, no. 3, p. 7, 1999.