The successful and widely used two-step process of producing the hybrid organic-inorganic perovskite CH3NH3PbI3, consists of converting a solution deposited PbI2 film by reacting it with CH3NH3I. Here, we investigate the solidification of PbI2 films from a DMF solution by performing in situ grazing incidence wide angle X-ray scattering (GIWAXS) measurements. The measurements reveal an elaborate sol–gel process involving three PbI2⋅DMF solvate complexes—including disordered and ordered ones—prior to PbI2 formation. The ordered solvates appear to be metastable as they transform into the PbI2 phase in air within minutes without annealing. Morphological analysis of air-dried and annealed films reveals that the air-dried PbI2 is substantially more porous when the coating process produces one of the intermediate solvates, making this more suitable for subsequent conversion into the perovskite phase. The observation of metastable solvates on the pathway to PbI2 formation open up new opportunities for influencing the two-step conversion of metal halides into efficient light harvesting or emitting perovskite semiconductors.
This is a preview of subscription content, access via your institution.
Buy single article
Instant access to the full article PDF.
Tax calculation will be finalised during checkout.
Subscribe to journal
Immediate online access to all issues from 2019. Subscription will auto renew annually.
Tax calculation will be finalised during checkout.
H. Zhou, Q. Chen, G. Li, S. Luo, T. Song, H-S. Duan, Z. Hong, J. You, Y. Liu, and Y. Yang: Interface engineering of highly efficient perovskite solar cells. Science 345(6196), 542 (2014).
M.M. Lee, J. Teuscher, T. Miyasaka, T.N. Murakami, and H.J. Snaith: Efficient hybrid solar cells based on meso-superstructured organometal halide perovskites. Science 338(6107), 643 (2012).
J. Burschka, N. Pellet, S-J. Moon, R. Humphry-Baker, P. Gao, M.K. Nazeeruddin, and M. Grätzel: Sequential deposition as a route to high-performance perovskite-sensitized solar cells. Nature 499(7458), 316 (2013).
J. Schlipf, P. Docampo, C.J. Schaffer, V. Körstgens, L. Bießmann, F. Hanusch, N. Giesbrecht, S. Bernstorff, T. Bein, and P. Müller-Buschbaum: A closer look into two-step perovskite conversion with X-ray scattering. J. Phys. Chem. Lett. 6(7), 1265 (2015).
F. Hao, C.C. Stoumpos, R.P.H. Chang, and M.G. Kanatzidis: Anomalous band gap behavior in mixed Sn and Pb perovskites enables broadening of absorption spectrum in solar cells. J. Am. Chem. Soc. 136(22), 8094 (2014).
Y.C. Choi, S. Won Lee, H. Jeong Jo, D-H. Kim, and S-J. Sung: Controlled growth of organic–inorganic hybrid CH3NH3PbI3 perovskite thin films from phase-controlled crystalline powders. RSC Adv. 6(106), 104359 (2016).
X. Guo, C. McCleese, C. Kolodziej, A.C.S. Samia, Y. Zhao, and C. Burda: Identification and characterization of the intermediate phase in hybrid organic–inorganic MAPbI3 perovskite. Dalton Trans. 45(9), 3806 (2016).
R. Munir, A.D. Sheikh, M. Abdelsamie, H. Hu, L. Yu, K. Zhao, T. Kim, O.E. Tall, R. Li, D-M. Smilgies, and A. Amassian: Hybrid perovskite thin-film photovoltaics: In situ diagnostics and importance of the precursor solvate phases. Adv. Mater. 29(2), 1604113 (2017).
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. Nat. Mater. 13(9), 897 (2014).
Y. Rong, Z. Tang, Y. Zhao, X. Zhong, S. Venkatesan, H. Graham, M. Patton, Y. Jing, A.M. Guloy, and Y. Yao: Solvent engineering towards controlled grain growth in perovskite planar heterojunction solar cells. Nanoscale 7(24), 10595 (2015).
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 348(6240), 1234 (2015).
A. Wakamiya, M. Endo, T. Sasamori, N. Tokitoh, Y. Ogomi, S. Hayase, and Y. Murata: Reproducible fabrication of efficient perovskite-based solar cells: X-ray crystallographic studies on the formation of CH3NH3PbI3 layers. Chem. Lett. 43(5), 711 (2014).
H. Zheng, W. Wang, S. Yang, Y. Liu, and J. Sun: A facile way to prepare nanoporous PbI2 films and their application in fast conversion to CH3NH3PbI3. RSC Adv. 6(2), 1611 (2016).
F. Hao, C.C. Stoumpos, Z. Liu, R.P.H. Chang, and M.G. Kanatzidis: Controllable perovskite crystallization at a gas–solid interface for hole conductor-free solar cells with steady power conversion efficiency over 10%. J. Am. Chem. Soc. 136(46), 16411 (2014).
K. Liang, D.B. Mitzi, and M.T. Prikas: Synthesis and characterization of organic–inorganic perovskite thin films prepared using a versatile two-step dipping technique. Chem. Mater. 10(1), 403 (1998).
D. Shen, X. Yu, X. Cai, M. Peng, Y. Ma, X. Su, L. Xiao, and D. Zou: Understanding the solvent-assisted crystallization mechanism inherent in efficient organic–inorganic halide perovskite solar cells. J. Mater. Chem. A 2(48), 20454 (2014).
H. Zhang, J. Mao, H. He, D. Zhang, H.L. Zhu, F. Xie, K.S. Wong, M. Grätzel, and W.C.H. Choy: A smooth CH3NH3PbI3 film via a new approach for forming the PbI2 nanostructure together with strategically high CH3NH3I concentration for high efficient planar-heterojunction solar cells. Adv. Energy Mater. 5(23), 1501354 (2015).
Y. Zhou, M. Yang, A.L. Vasiliev, H.F. Garces, Y. Zhao, D. Wang, S. Pang, K. Zhu, and N.P. Padture: Growth control of compact CH3NH3PbI3 thin films via enhanced solid-state precursor reaction for efficient planar perovskite solar cells. J. Mater. Chem. A 3(17), 9249 (2015).
W. Wu, H. Li, S. Liu, B. Zheng, Y. Xue, X. Liu, and C. Gao: Tuning PbI2 layers by n-butanol additive for improving CH3NH3PbI3 light harvesters of perovskite solar cells. RSC Adv. 6(92), 89609 (2016).
J. Cao, F. Wang, H. Yu, Y. Zhou, H. Lu, N. Zhao, and C-P. Wong: Porous PbI2 films for the fabrication of efficient, stable perovskite solar cells via sequential deposition. J. Mater. Chem. A 4(26), 10223 (2016).
T. Liu, Q. Hu, J. Wu, K. Chen, L. Zhao, F. Liu, C. Wang, H. Lu, S. Jia, T. Russell, R. Zhu, and Q. Gong: Mesoporous PbI2 scaffold for high-performance planar heterojunction perovskite solar cells. Adv. Energy Mater. 6(3), 1501890 (2016).
W. Li, J. Fan, J. Li, Y. Mai, and L. Wang: Controllable grain morphology of perovskite absorber film by molecular self-assembly toward efficient solar cell exceeding 17%. J. Am. Chem. Soc. 137(32), 10399 (2015).
G. Grancini, S. Marras, M. Prato, C. Giannini, C. Quarti, F. De Angelis, M. De Bastiani, G.E. Eperon, H.J. Snaith, L. Manna, and A. Petrozza: The impact of the crystallization processes on the structural and optical properties of hybrid perovskite films for photovoltaics. J. Phys. Chem. Lett. 5(21), 3836 (2014).
P. Müller-Buschbaum: The active layer morphology of organic solar cells probed with grazing incidence scattering techniques. Adv. Mater. 26(46), 7692 (2014).
A. Hexemer and P. Müller-Buschbaum: Advanced grazing-incidence techniques for modern soft-matter materials analysis. IUCrJ 2(1), 106 (2015).
K.W. Chou, H.U. Khan, M.R. Niazi, B. Yan, R. Li, M.M. Payne, J.E. Anthony, D-M. Smilgies, and A. Amassian: Late stage crystallization and healing during spin-coating enhance carrier transport in small-molecule organic semiconductors. J. Mater. Chem. C 2(28), 5681 (2014).
L.A. Perez, K.W. Chou, J.A. Love, T.S. van der Poll, D-M. Smilgies, T-Q. Nguyen, E.J. Kramer, A. Amassian, and G.C. Bazan: Solvent additive effects on small molecule crystallization in bulk heterojunction solar cells probed during spin casting. Adv. Mater. 25(44), 6380 (2013).
S. Masi, A. Rizzo, R. Munir, A. Listorti, A. Giuri, C.E. Corcione, N.D. Treat, G. Gigli, A. Amassian, N. Stingelin, and S. Colella: Organic gelators as growth control agents for stable and reproducible hybrid perovskite-based solar cells. Adv. Energy Mater. 1602600 (2017). doi: https://doi.org/10.1002/aenm.201602600.
This work was supported by the King Abdullah University of Science and Technology (KAUST). CHESS is supported by the NSF & NIH/NIGMS via NSF award DMR-1332208.
About this article
Cite this article
Barrit, D., Sheikh, A.D., Munir, R. et al. Hybrid perovskite solar cells: In situ investigation of solution-processed PbI2 reveals metastable precursors and a pathway to producing porous thin films. Journal of Materials Research 32, 1899–1907 (2017). https://doi.org/10.1557/jmr.2017.117