In summary, the research works in this dissertation focused on developing efficient and stable perovskite solar cells by manipulating perovskite composition, morphology, interfacial layers, passivation technique. Efforts in this dissertation enhanced perovskite solar cell efficiency and shed light on the understanding of perovskite photovoltaic physics based not solid experimental evidences and discussions.
To improve MAPbI3 perovskite film coverage on substrate, a non-stoichiometry MAI/PbI2 precursor ratio was used which improved perovskite film morphology and device efficiency. A double fullerene structure was developed which was effective in passivate perovskite defect to improve efficiency. The devices with this structure showed a higher efficiency of 12.2% with high fill factor of 80%.
A F4-TCNQ doped PTAA hole transporting layer was used in MAPbI3 perovskite solar cells to improve the efficiency to 17.5%. The hydrophobic nature of PTAA polymer enlarged the perovskite grain size to reduce charge carrier recombination. F4-TCNQ doping increased the polymer conductivity which reduces device series resistance to increase fill factor.
Insulating polymers were used in perovskite solar cells as tunneling contacts to increase the efficiency of MAPbI3 perovskite solar cell to 20.3%. The tunneling layer spatially separates photogenerated electrons and holes at the perovskite/polymer interface by transporting electrons and blocking holes, which should lead to the reduction of the carrier surface recombination. The
tunneling layer can also serve as an encapsulation layer to prevent perovskite film from damage caused by water or moisture.
A wide bandgap inorganic perovskite material, CsPbI3, was studied, in which a method was developed to stabilize the black phase of CsPbI3. A small amount of sulfobetaine zwitterion was added in CsPbI3 precursor solution could facilitate the formation of black-phase CsPbI3 films with significantly improved phase stability in the air. The black-phase stabilization can be explained by the formation of small CsPbI3 grains which increased the grain surface area to stabilizes the α- phase.
An interesting phenomenon, self-doping in MAPbI3, was reported. The electronic properties of MAPbI3 perovskite films, i.e., carrier concentration, mobility, conductivity type, and energy level, could be significantly tuned by changing the ratio of MAI to PbI2 in the precursor solution. The carrier concentration varied as much as six orders of magnitude.
REFFERENCES
1 Kojima, A., Teshima, K., Shirai, Y. & Miyasaka, T. Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. Journal of the American Chemical Society
131, 6050-6051 (2009).
2 Im, J.-H., Lee, C.-R., Lee, J.-W., Park, S.-W. & Park, N.-G. 6.5% efficient perovskite quantum-dot-sensitized solar cell. Nanoscale 3, 4088-4093 (2011).
3 Kim, H.-S. et al. Lead iodide perovskite sensitized all-solid-state submicron thin film mesoscopic solar cell with efficiency exceeding 9%. Scientific reports 2, 591 (2012). 4 Lee, M. M., Teuscher, J., Miyasaka, T., Murakami, T. N. & Snaith, H. J. Efficient hybrid
solar cells based on meso-superstructured organometal halide perovskites. Science 338, 643-647 (2012).
5 Burschka, J. et al. Sequential deposition as a route to high-performance perovskite- sensitized solar cells. Nature 499, 316 (2013).
6 Liu, M., Johnston, M. B. & Snaith, H. J. Efficient planar heterojunction perovskite solar cells by vapour deposition. Nature 501, 395 (2013).
7 Marronnier, A. et al. Anharmonicity and disorder in the black phases of cesium lead iodide used for stable inorganic perovskite solar cells. ACS nano 12, 3477-3486 (2018).
8 Leguy, A. M. et al. Reversible hydration of CH3NH3PbI3 in films, single crystals, and solar cells. Chemistry of Materials 27, 3397-3407 (2015).
9 Conings, B. et al. Intrinsic thermal instability of methylammonium lead trihalide perovskite. Advanced Energy Materials 5, 1500477 (2015).
10 Peumans, P. & Forrest, S. Very-high-efficiency double-heterostructure copper phthalocyanine/C 60 photovoltaic cells. Applied Physics Letters 79, 126-128 (2001). 11 Peumans, P., Bulović, V. & Forrest, S. R. Efficient photon harvesting at high optical
intensities in ultrathin organic double-heterostructure photovoltaic diodes. Applied Physics Letters 76, 2650-2652 (2000).
12 Guo, F. et al. A nanocomposite ultraviolet photodetector based on interfacial trap- controlled charge injection. Nature nanotechnology 7, 798 (2012).
13 Guo, F., Xiao, Z. & Huang, J. Fullerene Photodetectors with a Linear Dynamic Range of 90 dB Enabled by a Cross‐Linkable Buffer Layer. Advanced Optical Materials 1, 289-294 (2013).
15 Yang, B. et al. Solution‐processed fullerene‐based organic Schottky junction devices for large‐open‐circuit‐voltage organic solar cells. Advanced Materials 25, 572-577 (2013). 16 Walter, T., Herberholz, R., Müller, C. & Schock, H. Determination of defect distributions
from admittance measurements and application to Cu (In, Ga) Se2 based heterojunctions.
Journal of Applied Physics 80, 4411-4420 (1996).
17 Khelifi, S. et al. Investigation of defects by admittance spectroscopy measurements in poly (3-hexylthiophene):(6, 6)-phenyl C61-butyric acid methyl ester organic solar cells degraded under air exposure. Journal of Applied Physics 110, 094509 (2011).
18 Jeon, N. J. et al. Efficient inorganic–organic hybrid perovskite solar cells based on pyrene arylamine derivatives as hole-transporting materials. Journal of the American Chemical Society 135, 19087-19090 (2013).
19 Qin, P. et al. Perovskite solar cells with 12.8% efficiency by using conjugated quinolizino acridine based hole transporting material. Journal of the American Chemical Society 136, 8516-8519 (2014).
20 Kim, J. H. et al. High‐performance and environmentally stable planar heterojunction perovskite solar cells based on a solution‐processed copper‐doped nickel oxide hole‐ transporting layer. Advanced Materials 27, 695-701 (2015).
21 Liu, J. et al. A dopant-free hole-transporting material for efficient and stable perovskite solar cells. Energy & Environmental Science 7, 2963-2967 (2014).
22 Wang, Q. et al. Qualifying composition dependent p and n self-doping in CH3NH3PbI3.
Appl. Phys. Lett. 105, 163508 (2014).
23 Koide, N., Islam, A., Chiba, Y. & Han, L. Improvement of efficiency of dye-sensitized solar cells based on analysis of equivalent circuit. J. Photoch. Photobio. A: Chem. 182, 296-305 (2006).
24 Xiao, Z. et al. Efficient, High Yield Perovskite Photovoltaic Devices Grown by Interdiffusion of Solution-Processed Precursor Stacking Layers. Energ. Environ. Sci. 7, 2619-2623 (2014).
25 Dong, R. et al. High‐Gain and Low‐Driving‐Voltage Photodetectors Based on Organolead Triiodide Perovskites. Adv. Mater. 27, 1912–1918 (2015).
26 Xiao, Z. et al. Solvent Annealing of Perovskite‐Induced Crystal Growth for Photovoltaic‐
Device Efficiency Enhancement. Adv. Mater. 26, 6503-6509 (2014).
27 Bi, C. et al. Understanding the formation and evolution of interdiffusion grown organolead halide perovskite thin films by thermal annealing. J. Mater. Chem. A 2, 18508-18514 (2014).
28 Bi, C. et al. Nonwetting Surface Driven High Aspect Ratio Crystalline Grain Growth for Efficient Hybrid Perovskite Solar Cells. Nat. Commun. 6, 7747, (2015).
29 Wang, Q. et al. Large fill-factor bilayer iodine perovskite solar cells fabricated by a low- temperature solution-process. Energ. Environ. Sci. 7, 2359-2365 (2014).
30 Shao, Y., Xiao, Z., Bi, C., Yuan, Y. & Huang, J. Origin and elimination of photocurrent hysteresis by fullerene passivation in CH3NH3PbI3 planar heterojunction solar cells. Nat. Commun. 5, 5784 (2014).
31 Duong, D. T. et al. Direct Observation of Doping Sites in Temperature‐Controlled, p‐
Doped P3HT Thin Films by Conducting Atomic Force Microscopy. Adv. Mater. 26, 6069- 6073 (2014).
32 Deschler, F. et al. Imaging of morphological changes and phase segregation in doped polymeric semiconductors. Synthetic Metals 199, 381-387 (2015).
33 Han, X., Wu, Z. & Sun, B. Enhanced performance of inverted organic solar cell by a solution-based fluorinated acceptor doped P3HT: PCBM layer. Organic Electronics 14, 1116-1121 (2013).
34 Pingel, P. et al. Charge-transfer localization in molecularly doped thiophene-based donor polymers. The Journal of Physical Chemistry Letters 1, 2037-2041 (2010).
35 Dong, Q. et al. Electron-hole diffusion lengths> 175 μm in solution-grown CH3NH3PbI3 single crystals. Science 347, 967-970 (2015).
36 Shi, D. et al. Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals. Science 347, 519-522 (2015).
37 Snaith, H. J. Perovskites: the emergence of a new era for low-cost, high-efficiency solar cells. J. Phys. Chem. Lett. 4, 3623-3630 (2013).
38 De Wolf, S. et al. Organometallic halide perovskites: sharp optical absorption edge and its relation to photovoltaic performance. J. Phys. Chem. Lett. 5, 1035-1039 (2014).
39 Bi, C. et al. Non-wetting surface-driven high-aspect-ratio crystalline grain growth for efficient hybrid perovskite solar cells. Nature Commun. 6 (2015).
40 Yu, H. et al. The Role of Chlorine in the Formation Process of “CH3NH3PbI3‐xClx” Perovskite. Adv. Func. Mater. 24, 7102-7108 (2014).
41 Zhou, H. et al. Interface engineering of highly efficient perovskite solar cells. Science 345, 542-546 (2014).
42 Yang, B. et al. Perovskite solar cells with near 100% internal quantum efficiency based on large single crystalline grains and vertical bulk heterojunctions. J. Am. Chem. Soc. 137,
43 Yang, W. S. et al. High-performance photovoltaic perovskite layers fabricated through intramolecular exchange. Science, aaa9272 (2015).
44 Wang, F., Yu, H., Xu, H. & Zhao, N. HPbI3: A New Precursor Compound for Highly Efficient Solution‐Processed Perovskite Solar Cells. Adv. Func. Mater. 25, 1120-1126 (2015).
45 Shao, Y., Xiao, Z., Bi, C., Yuan, Y. & Huang, J. Origin and elimination of photocurrent hysteresis by fullerene passivation in CH3NH3PbI3 planar heterojunction solar cells.
Nature Commun. 5 (2014).
46 Xu, J. et al. Perovskite-fullerene hybrid materials suppress hysteresis in planar diodes.
Nature Commun. 6, 7081, (2015).
47 Noel, N. K. et al. Enhanced photoluminescence and solar cell performance via Lewis base passivation of organic–inorganic lead halide perovskites. ACS nano 8, 9815-9821 (2014). 48 Masuko, K. et al. Achievement of more than 25% conversion efficiency with crystalline
silicon heterojunction solar cell. Photovoltaics, IEEE Journal of 4, 1433-1435 (2014). 49 Pulfrey, D. L. MIS solar cells: a review. Electron Devices, IEEE Transactions on 25, 1308-
1317 (1978).
50 Wang, Q., Bi, C. & Huang, J. Doped hole transport layer for efficiency enhancement in planar heterojunction organolead trihalide perovskite solar cells. Nano Energy 15, 275-280 (2015).
51 Parker, I. D. Carrier tunneling and device characteristics in polymer light‐emitting diodes.
J. Appl. Phys. 75, 1656-1666 (1994).
52 Xu, Z., Bai, X., Wang, E. & Wang, Z. L. Field emission of individual carbon nanotube with in situ tip image and real work function. Applied Physics Letters 87, 163106 (2005). 53 Dong, R. et al. High‐Gain and Low‐Driving‐Voltage Photodetectors Based on
Organolead Triiodide Perovskites. Adv. Mater. 27, 1912-1918 (2015).
54 Pagliaro, M. & Ciriminna, R. New fluorinated functional materials. J. Mater. Chem. 15, 4981-4991 (2005).
55 Maciejewski, H., Karasiewicz, J., Dutkiewicz, M. & Nowicki, M. Effect of the type of fluorofunctional organosilicon compounds and the method of their application onto the surface on its hydrophobic properties. RSC Advances 4, 52668-52675 (2014).
56 van Wijk, J., van Deventer, N., Harmzen, E., Meuldijk, J. & Klumperman, B. Formation of hybrid poly (styrene-co-maleic anhydride)–silica microcapsules. J. Mater. Chem. B 2, 4826-4835 (2014).
57 Yang, S. et al. Functionalization of perovskite thin films with moisture-tolerant molecules.
Nature Energy, 1, 15016 (2016).
58 You, J. et al. Improved air stability of perovskite solar cells via solution-processed metal oxide transport layers. Nature nanotechnology 11, 75-81 (2016).
59 Chen, W. et al. Efficient and stable large-area perovskite solar cells with inorganic charge extraction layers. Science 350, 944-948 (2015).
60 Shao, Y., Yuan, Y. & Huang, J. Correlation of Energy Disorder and Open-Circuit Voltage in Hybrid Perovskite Solar Cells. Nature Energy,1 15001, (2015).
61 Conings, B. et al. Intrinsic thermal instability of methylammonium lead trihalide perovskite. Advanced Energy Materials 5, 1500477, (2015).
62 Nagabhushana, G., Shivaramaiah, R. & Navrotsky, A. Direct calorimetric verification of thermodynamic instability of lead halide hybrid perovskites. Proceedings of the National Academy of Sciences 113, 7717-7721 (2016).
63 Sutton, R. J. et al. Bandgap‐Tunable Cesium Lead Halide Perovskites with High Thermal Stability for Efficient Solar Cells. Advanced Energy Materials 6, 1502458, (2016).
64 Beal, R. E. et al. Cesium lead halide perovskites with improved stability for tandem solar cells. The journal of physical chemistry letters 7, 746-751 (2016).
65 Chen, C. Y. et al. All‐Vacuum‐Deposited Stoichiometrically Balanced Inorganic Cesium Lead Halide Perovskite Solar Cells with Stabilized Efficiency Exceeding 11%. Advanced Materials 29, 1605290, (2017).
66 Ma, Q., Huang, S., Wen, X., Green, M. A. & Ho‐Baillie, A. W. Hole Transport Layer Free Inorganic CsPbIBr2 Perovskite Solar Cell by Dual Source Thermal Evaporation. Advanced Energy Materials 6, 1502202, (2016).
67 Frolova, L. A. et al. Highly Efficient All-Inorganic Planar Heterojunction Perovskite Solar Cells Produced by Thermal Coevaporation of CsI and PbI2. The Journal of Physical Chemistry Letters 8, 67-72 (2016).
68 Swarnkar, A. et al. Quantum dot–induced phase stabilization of α-CsPbI3 perovskite for high-efficiency photovoltaics. Science 354, 92-95 (2016).
69 McHale, J., Auroux, A., Perrotta, A. & Navrotsky, A. Surface energies and thermodynamic phase stability in nanocrystalline aluminas. Science 277, 788-791 (1997).
70 Frey, M. & Payne, D. Grain-size effect on structure and phase transformations for barium titanate. Physical Review B 54, 3158 (1996).
72 Zhang, N., Yang, W., Ding, W., Xing, D. & Du, Y. Grain size-dependent magnetism in fine particle perovskite, La 1− x Sr x MnO z. Solid state communications 109, 537-542 (1999).
73 Ayyub, P., Palkar, V., Chattopadhyay, S. & Multani, M. Effect of crystal size reduction on lattice symmetry and cooperative properties. Physical Review B 51, 6135 (1995).
74 Protesescu, L. et al. Nanocrystals of cesium lead halide perovskites (CsPbX3, X= Cl, Br, and I): novel optoelectronic materials showing bright emission with wide color gamut.
Nano letters 15, 3692-3696 (2015).
75 Hoffman, J. B., Schleper, A. L. & Kamat, P. V. Transformation of Sintered CsPbBr3 Nanocrystals to Cubic CsPbI3 and Gradient CsPbBr x I3–x through Halide Exchange.
Journal of the American Chemical Society 138, 8603-8611 (2016).
76 Wang, C., Chesman, A. S. & Jasieniak, J. J. Stabilizing the cubic perovskite phase of CsPbI 3 nanocrystals by using an alkyl phosphinic acid. Chemical Communications 53, 232-235 (2017).
77 Viana, R. B., da Silva, A. B. & Pimentel, A. S. Infrared spectroscopy of anionic, cationic, and zwitterionic surfactants. Advances in physical chemistry 2012, 903272, (2012). 78 Yan, K. et al. Hybrid halide perovskite solar cell precursors: Colloidal chemistry and
coordination engineering behind device processing for high efficiency. Journal of the American Chemical Society 137, 4460-4468 (2015).
79 Wang, R. et al. Colloidal quantum dot ligand engineering for high performance solar cells.
Energy & Environmental Science 9, 1130-1143 (2016).
80 Walzer, K., Maennig, B., Pfeiffer, M. & Leo, K. Highly efficient organic devices based on electrically doped transport layers. Chem. Rev. 107, 1233-1271 (2007).
81 Zhang, C. et al. Charge recombination and band-edge shift in the dye-sensitized Mg2+- doped TiO2 solar cells. J. Phys. Chem. C 115, 16418-16424 (2011).
82 Stranks, S. D. et al. Electron-hole diffusion lengths exceeding 1 micrometer in an organometal trihalide perovskite absorber. Science 342, 341-344 (2013).
83 Zhu, F. et al. The Origin of Higher Open‐Circuit Voltage in Zn‐Doped TiO2 Nanoparticle‐Based Dye‐Sensitized Solar Cells. ChemPhysChem 13, 3731-3737 (2012). 84 Shi, Y. et al. Work function engineering of graphene electrode via chemical doping. Acs
Nano 4, 2689-2694 (2010).
85 Gao, Y. et al. Surface doping of conjugated polymers by graphene oxide and its application for organic electronic devices. Adv. Mater. 23, 1903-1908 (2011).
86 Kim, J., Lee, S.-H., Lee, J. H. & Hong, K.-H. The Role of Intrinsic Defects in Methylammonium Lead Iodide Perovskite. J. Phys. Chem. Lett. 5, 1312-1317 (2014). 87 Yin, W.-J., Shi, T. & Yan, Y. Unusual defect physics in CH3NH3PbI3 perovskite solar
cell absorber. Appl. Phys. Lett. 104, 063903 (2014).
88 Yin, W. J., Shi, T. & Yan, Y. Unique Properties of Halide Perovskites as Possible Origins of the Superior Solar Cell Performance. Adv. Mater., 26, 4653-4658, (2014).
89 Wang, Q. et al. Large fill-factor bilayer iodine perovskite solar cells fabricated by a low- temperature solution-process. Energy Environ. Sci. 7, 2359-2365 (2014).
90 Wehrenfennig, C., Eperon, G. E., Johnston, M. B., Snaith, H. J. & Herz, L. M. High charge carrier mobilities and lifetimes in organolead trihalide perovskites. Adv. Mater. 26, 1584- 1589 (2014).
91 Bi, C. et al. Understanding the Formation and Evolution of Interdiffusion Grown Organolead Halide Perovskite Thin Films by Thermal Annealing Adv. Func. Mater. 2, 18508-18514, 2014.
92 Dualeh, A. et al. Effect of Annealing Temperature on Film Morphology of Organic–
Inorganic Hybrid Pervoskite Solid‐State Solar Cells. Adv. Func. Mater., 24, 3250–3258, 2014
93 Chen, Q. et al. Planar heterojunction perovskite solar cells via vapor-assisted solution process. J. Am. Chem. Soc. 136, 622-625 (2013).
94 Kassap, S. O. Principles of Electronic Materials and Devices. (McGraw Hill, 2006). 95 Wang, A., Zhao, J. & Green, M. 24% efficient silicon solar cells. Appl. Phys. Lett. 57, 602-