有機無機混成鈣鈦礦太陽能電池元件發展至今，能量轉換效率已可達25%以上，但在商業化上元件穩定性仍是最大問題，因鈣鈦礦在大氣環境下極容易與水反應而分解。本研究使用能帶間隙為1.47 eV，吸收邊界理論上可達850 nm的FAPbI3鈣鈦礦作為太陽能電池元件主動層材料，因為其相較MAPbI3和CsPbI3等，具有最接近S-Q理論之理想能隙及最寬的光吸收範圍。為解決其容易相轉變成不穩定的鈣鈦礦相(δ相FAPbI3)，本研究添加MACl與FASCN作為穩定劑，其中MACl為近年來FAPbI3鈣鈦礦普遍添加的穩定劑，本研究中比較添加MACl與否兩種情況下，FASCN在鈣鈦礦中皆能增加其穩定性而不對元件轉換效率有負面影響。
先前文獻對於添加MACl於FAPbI3鈣鈦礦所造成的礦相影響，以及結晶過程等機制已有清楚的研究，但對於在如台灣等地較溼熱天氣，添加後的穩定性仍然無甚顯著影響，本研究摻雜入微量FASCN發現在大氣環境下能有效抑制α相FAPbI3鈣鈦礦轉變為δ相FAPbI3鈣鈦礦的過程，其現象由肉眼清晰可見，在對照組無添加MACl者因大氣環境轉變為透明黃色膜時，摻雜3%FASCN者仍能保持如剛退火完成時漆黑鏡面。
研究中加入的MA、Cl、SCN等額外離子，均在SIMS與XPS能做清楚的分析，其中MACl在退火過程中未完全逸散，部分留存於膜中，對於吸收邊界也產生些微藍移，在有添加SCN組別時，會增進Cl的留存，其現象可從SIMS與XPS分析明顯觀察出。SCN則皆在薄膜底部才有些許留存，而Cl存在時更減少薄膜深處的SCN含量。

Currently, the organic-inorganic hybrid perovskite solar cells (PSCs) have achieved high efficiency over 25%. However, the instability of perovskite is still a concerned for practical application of PSCs under ambient condition. Although formamidinium lead triiodide (FAPbI3) perovskite exhibits ideal bandgap of 1.47 eV which is close to the Shockley-Queisser limit, the perovskite phase of FAPbI3 (α-phase FAPbI3) easily converts into non-perovskite phase (δ-phase FAPbI3) at room temperature whose optoelectronic properties are not suitable for solar cells. The purpose of this study is to introduce two additives, methylammonium chloride (MACl) and formamidinium thiocyanate (FASCN), in FAPbI3 perovskite to stabilize the α-phase FAPbI3 in virtue of composition engineering. Addition of MACl can relax strain of FAPbI3 perovskite lattice structure, while pseudo-halide (such as SCN) can stabilize the perovskite lattice structure as well. The results indicate that the halide of Cl and pseudo-halide of SCN from the additive show competitive relationship in the resultant perovskite film and different mechanism to improve the stability of FAPbI3 perovskite.

[1] R. A. García, S. Turck-Chièze, S. J. Jiménez-Reyes, J. Ballot, P. L. Pallé, A. Eff-Darwich, S. Mathur, and J. Provost, "Tracking Solar Gravity Modes: The Dynamics of the Solar Core," Science, 2007, 316, 5831, 1591.
[2] A. Einstein, "Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt [AdP 17, 132 (1905)]," Annalen der Physik, 2005, 14, S1, 164-181.
[3] "The Nobel Prize in Physics 1921." https://www.nobelprize.org/prizes/physics/1921/summary/ (accessed 2020).
[4] A. E. Becquerel, "Mémoire Sur Les Effets électriques Produits Sous l'influence des Rayons Solaires," Comptes Rendus de L’Academie des Sciences, 1839, 9, 561-567.
[5] A. E. Becquerel, "Mémoire Sur Les Effets électriques Produits Sous l'influence des Rayons Solaires," Comptes Rendus de L’Academie des Sciences, 1839, 9, 561-567.
[6] NREL, "Best Research-Cell Efficiency Chart." https://www.nrel.gov/pv/cell-efficiency.html (accessed 2020).
[7] G. E. Eperon, S. D. Stranks, C. Menelaou, M. B. Johnston, L. M. Herz, and H. J. Snaith, "Formamidinium lead trihalide: a broadly tunable perovskite for efficient planar heterojunction solar cells," Energy & Environmental Science, 2014, 7, 3, 982-988.
[8] S. Aharon, A. Dymshits, A. Rotem, and L. Etgar, "Temperature dependence of hole conductor free formamidinium lead iodide perovskite based solar cells," Journal of Materials Chemistry A, 2015, 3, 17, 9171-9178.
[9] G. R. Energy, "Graphing Intensity and Energy." http://www.greenrhinoenergy.com/solar/radiation/geometry.php (accessed 2020).
[10] W. Shockley and H. J. Queisser, "Detailed Balance Limit of Efficiency of p‐n Junction Solar Cells," Journal of Applied Physics, 1961, 32, 3, 510-519.
[11] R. Hsu, C. T. Liu, W. Y. Chen, H.-I. Hsieh, and H. L. Wang, "A Reinforcement Learning-Based Maximum Power Point Tracking Method for Photovoltaic Array," International Journal of Photoenergy, 2015, 2015.
[12] P. Mao, Y. Wei, H. Li, and J. Wang, "Junction diodes in organic solar cells," Nano Energy, 2017, 41, 717-730.
[13] B. Schweber, "Solar cells and power, Part 2 – power extraction." POWER ELECTRIC TiPS. https://www.powerelectronictips.com/solar-cells-power-part-2-power-extraction/ (accessed 2020).
[14] G. Instruments, "DSSC: Dye Sensitized Solar Cells," https://www.gamry.com/application-notes/physechem/dssc-dye-sensitized-solar-cells/.
[15] G. Li-Ke, T. Yan-Lin, and D. Xin-Feng, "Theoretical study on photoelectric properties of FAPbI3 doped with Ge," Materials Research Express, 2020.
[16] E. Tai, R. Wang, Y. Chen, and G. Xu, "A Water-Stable Organic-Inorganic Hybrid Perovskite for Solar Cells by Inorganic Passivation," Crystals, 2019, 9, 83.
[17] A. Kojima, K. Teshima, YasuoShirai, and T. Miyasaka, "Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells," Journal of the American Chemical Society, 2009, 131, 17, 6050-6051.
[18] H.-S. Kim, C.-R. Lee, J.-H. Im, K.-B. Lee, T. Moehl, A. Marchioro, S.-J. Moon, R. Humphry-Baker, J.-H. Yum, J. E. Moser, M. Grätzel, and N.-G. Park, "Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%," Scientific Reports, 2012, 2, 591.
[19] N. J. Jeon, J. H. Noh, Y. C. Kim, W. S. Yang, S. Ryu, and S. I. Seok, "Solvent Engineering for High-Performance Inorganic–Organic Hybrid Perovskite Solar Cells," Nature Materials, 2014, 13, 897.
[20] M. Saliba, T. Matsui, K. Domanski, J.-Y. Seo, A. Ummadisingu, S. Zakeeruddin, J.-P. Correa-Baena, W. Tress, A. Abate, A. Hagfeldt, and M. Graetzel, "Incorporation of rubidium cations into perovskite solar cells improves photovoltaic performance," Science (New York, N.Y.), 2016, 354.
[21] W. S. Yang, J. H. Noh, N. J. Jeon, Y. C. Kim, S. Ryu, J. Seo, and S. I. Seok, "High-performance photovoltaic perovskite layers fabricated through intramolecular exchange," Science, 2015, 348, 6240, 1234.
[22] H. Min, M. Kim, S.-U. Lee, H. Kim, G. Kim, K. Choi, J. H. Lee, and S. I. Seok, "Efficient, stable solar cells by using inherent bandgap of α-phase formamidinium lead iodide," Science, 2019, 366, 6466, 749.
[23] M. I. Saidaminov, J. Kim, A. Jain, R. Quintero-Bermudez, H. Tan, G. Long, F. Tan, A. Johnston, Y. Zhao, O. Voznyy, and E. H. Sargent, "Suppression of atomic vacancies via incorporation of isovalent small ions to increase the stability of halide perovskite solar cells in ambient air," Nature Energy, 2018, 3, 8, 648-654.
[24] X. Zheng, C. Wu, S. K. Jha, Z. Li, K. Zhu, and S. Priya, "Improved Phase Stability of Formamidinium Lead Triiodide Perovskite by Strain Relaxation," ACS Energy Letters, 2016, 1, 5, 1014-1020.
[25] E. Mosconi, E. Ronca, and F. De Angelis, "First-Principles Investigation of the TiO2/Organohalide Perovskites Interface: The Role of Interfacial Chlorine," The Journal of Physical Chemistry Letters, 2014, 5, 15, 2619-2625.
[26] D. P. McMeekin, G. Sadoughi, W. Rehman, G. E. Eperon, M. Saliba, M. T. Hörantner, A. Haghighirad, N. Sakai, L. Korte, B. Rech, M. B. Johnston, L. M. Herz, and H. J. Snaith, "A mixed-cation lead mixed-halide perovskite absorber for tandem solar cells," Science, 2016, 351, 6269, 151.
[27] E. Edri, S. Kirmayer, M. Kulbak, G. Hodes, and D. Cahen, "Chloride Inclusion and Hole Transport Material Doping to Improve Methyl Ammonium Lead Bromide Perovskite-Based High Open-Circuit Voltage Solar Cells," The Journal of Physical Chemistry Letters, 2014, 5, 3, 429-433.
[28] E. Edri, S. Kirmayer, D. Cahen, and G. Hodes, "High Open-Circuit Voltage Solar Cells Based on Organic-Inorganic Lead Bromide Perovskite," The Journal of Physical Chemistry Letters, 2013, 4, 6, 897-902.
[29] B. Suarez, V. Gonzalez-Pedro, T. S. Ripolles, R. S. Sanchez, L. Otero, and I. Mora-Sero, "Recombination Study of Combined Halides (Cl, Br, I) Perovskite Solar Cells," The Journal of Physical Chemistry Letters, 2014, 5, 10, 1628-1635.
[30] P. Docampo, F. C. Hanusch, S. D. Stranks, M. Döblinger, J. M. Feckl, M. Ehrensperger, N. K. Minar, M. B. Johnston, H. J. Snaith, and T. Bein, "Solution Deposition‐Conversion for Planar Heterojunction Mixed Halide Perovskite Solar Cells," Advanced Energy Materials, 2014, 4, 14, 1400355.
[31] Z. Wang, Y. Zhou, S. Pang, Z. Xiao, J. Zhang, W. Chai, H. Xu, Z. Liu, N. P. Padture, and G. Cui, "Additive-Modulated Evolution of HC(NH2)2PbI3 Black Polymorph for Mesoscopic Perovskite Solar Cells," Chemistry of Materials, 2015, 27, 20, 7149-7155.
[32] C. Mu, J. Pan, S. Feng, Q. Li, and D. Xu, "Quantitative Doping of Chlorine in Formamidinium Lead Trihalide (FAPbI3−xClx) for Planar Heterojunction Perovskite Solar Cells," Advanced Energy Materials, 2017, 7, 6, 1601297.
[33] M. Kim, G. Kim, T. K. Lee, I. Choi, H. Choi, Y. Jo, Y. Yoon, J. Kim, J. Lee, D. Huh, H. Lee, S. K. Kwak, J. Y. Kim, and D. Kim, "Methylammonium Chloride Induces Intermediate Phase Stabilization for Efficient Perovskite Solar Cells," Joule, 2019, 3.
[34] J. M. Frost, K. T. Butler, F. Brivio, C. H. Hendon, M. van Schilfgaarde, and A. Walsh, "Atomistic Origins of High-Performance in Hybrid Halide Perovskite Solar Cells," Nano Letters, 2014, 14, 5, 2584-2590.
[35] Q. Jiang, D. Rebollar, J. Gong, E. L. Piacentino, C. Zheng, and T. Xu, "Pseudohalide‐Induced Moisture Tolerance in Perovskite CH3NH3Pb(SCN)2I Thin Films," Angewandte Chemie International Edition, 2015, 54, 26, 7617-7620.
[36] Y. Chen, B. Li, W. Huang, D. Gao, and Z. Liang, "Efficient and Reproducible CH3NH3PbI3−x(SCN)x Perovskite Based Planar Solar Cells," Chemical Communications, 2015, 51, 60, 11997-11999.
[37] Q. Tai, P. You, H. Sang, Z. Liu, C. Hu, H. L. W. Chan, and F. Yan, "Efficient and Stable Perovskite Solar Cells Prepared in Ambient Air Irrespective of the Humidity," Nature Communications, 2016, 7, 11105.
[38] Y. Sun, J. Peng, Y. Chen, Y. Yao, and Z. Liang, "Triple-Cation Mixed-Halide Perovskites: Towards Efficient, Annealing-Free and Air-Stable Solar Cells Enabled by Pb(SCN)2 Additive," Scientific Reports, 2017, 7, 46193.
[39] Y.-H. Chiang, H.-M. Cheng, M.-H. Li, T.-F. Guo, and P. Chen, "Low-Pressure Vapor-Assisted Solution Process for Thiocyanate-Based Pseudohalide Perovskite Solar Cells," ChemSusChem, 2016, 9, 18, 2620-2627.
[40] Y.-H. Chiang, M.-H. Li, H.-M. Cheng, P.-S. Shen, and P. Chen, "Mixed Cation Thiocyanate-Based Pseudohalide Perovskite Solar Cells with High Efficiency and Stability," ACS Applied Materials & Interfaces, 2017, 9, 3, 2403-2409.
[41] Q. Han, Y. Bai, J. Liu, K.-z. Du, T. Li, D. Ji, Y. Zhou, C. Cao, D. Shin, J. Ding, A. D. Franklin, J. T. Glass, J. Hu, M. J. Therien, J. Liu, and D. B. Mitzi, "Additive Engineering for High-Performance Room-Temperature-Processed Perovskite Absorbers with Micron-Size Grains and Microsecond-Range Carrier Lifetimes," Energy & Environmental Science, 2017, 10, 11, 2365-2371.
[42] S. Yang, W. Liu, L. Zuo, X. Zhang, T. Ye, J. Chen, C.-Z. Li, G. Wu, and H. Chen, "Thiocyanate assisted performance enhancement of formamidinium based planar perovskite solar cells through a single one-step solution process," Journal of Materials Chemistry A, 2016, 4, 24, 9430-9436.
[43] W. Melitz, J. Shen, A. C. Kummel, and S. Lee, "Kelvin Probe Force Microscopy and its Application," Surface Science Reports, 2011, 66, 1, 1-27.
[44] F. Liu, Q. Dong, M. K. Wong, A. B. Djurišić, A. Ng, Z. Ren, Q. Shen, C. Surya, W. K. Chan, J. Wang, A. M. C. Ng, C. Liao, H. Li, K. Shih, C. Wei, H. Su, and J. Dai, "Is Excess PbI2 Beneficial for Perovskite Solar Cell Performance?," Advanced Energy Materials, 2016, 6, 7, 1502206.
[45] M. Daub and H. Hillebrecht, "Synthesis, Single-Crystal Structure and Characterization of (CH3NH3)2Pb(SCN)2I2," Angewandte Chemie International Edition, 2015, 54, 38, 11016-11017.
[46] G. Tang, C. Yang, A. Stroppa, D. Fang, and J. Hong, "Revealing the Role of Thiocyanate Anion in Layered Hybrid Halide Perovskite (CH3NH3)2Pb(SCN)2I2," The Journal of Chemical Physics, 2017, 146, 22, 224702.
[47] H. S. Jung and N.-G. Park, "Perovskite Solar Cells: From Materials to Devices," Small, 2015, 11, 1, 10-25.