Low Temperature Bulk Crystal Growth of HC(NH2)2PbI3 in Alkyl-substituted Lactones by Inverse Temperature Crystallization
Kenji Kawano a, Takashi Sekiguchi a, Michio Suzuka a, Ryusuke Uchida a, Jennifer Torres Damasco Ty b
a Advanced Functional Material Group, Advanced Research Division, Panasonic Corporation, 3-1-1 Yagumo-naka-machi, Moriguchi, Osaka, 570-8501, Japan
b Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorioka, Ikeda, Osaka, 563-8577, Japan
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics (AP-HOPV17)
Yokohama-shi, Japan, 2017 February 2nd - 4th
Organizers: Tsutomu Miyasaka and Iván Mora-Seró
Poster, Michio Suzuka, 031
Publication date: 7th November 2016

     Inverse temperature crystallization (ITC) of formamidinium lead iodide perovskite (HC(NH2)2PbI3) using γ-butyrolactone (GBL) as solvents have been of interest because of its simplicity to obtain single and bulk crystals. However, the detailed crystal growth mechanism is still unclear. Therefore, we investigated the relationship between crystal growth temperature and side-chain length of lactones.

     Lactones with alkyl chains, such as methylbutyrolactone and γ-hexanolactone, have a similar chemical structure to GBL, and are suitable for ITC because of their high boiling point of > 200 ºC and high solubility of HC(NH2)2I and PbI2 which are the precursors of HC(NH2)2PbI3. The HC(NH2)2PbI3 crystals in lactones with longer alkyl chain can be formed in shorter period of less than 30 min, higher HC(NH2)2PbI3 yield of more than 50 % and lower temperature of less than 60 ºC, compared with those in GBL (2 hours, 15 % and 110 ºC, respectively).

     Raman and UV-vis spectroscopy of a solution of the precursors in lactones reveal a weak solvent-solute-complex strength and a formation of iodoplumbate complexes of PbI3- and PbI42-, while there is a strong interaction to the precursors and no signals of iodoplumbate complexes in dimethyl sulfoxide or N,N-dimethylformamide. These results indicated that the weak complex strength in the solvent with alkyl substitution lead to small activation energy and rapid formation of the perovskite structure. These lactones would be promising solvents for low-temperature fabrication of perovskite solar cells.



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