Role of Isopropyl Alcohol (IPA) Solvent in the Synthesis of Organic-inorganic Halide CH(NH2)2PbIxBr3-x Perovskite Thin Films by Two-step Method
Kenta Masumori a, Ryo Ishikawa a, Hajime Shirai a
a Saitama University, 255 Shimo-Okubo, Sakura, Saitama, 338, 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, Hajime Shirai, 061
Publication date: 7th November 2016

In the present paper, we present the role of the isopropyl alcohol (IPA) solvent in the synthesis of organic-lead-halide perovskite CH(NH2)2PbIxBr3-x [FAPbIxBr3-x] thin films by a two-step reaction of an amorphous (a-)PbIxBr2-x layer and FAIxBr1-x solution diluted in IPA using spectroscopic ellipsometry (SE) as well as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning microscopy (SEM) observation. An optical dispersion model was developed to extract the complex refractive index N (=n+ik), optical transition, and film thickness of FAPbIxBr3-x perovskites by SE analysis as a function of immersion time in a solution of FAIxBr1-x diluted in IPA. SE combined with X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning microscopy (SEM) revealed that IPA promoted film crystallization of a-PbIxBr2-x accompanied by the formation of surface roughness, grain boundaries, and voids, followed by enhanced diffusion of FAIxBr1-x into the grain boundaries/voids in the mesoporous crystallized PbIxBr2-x network.IPA played a significant role to promote crystallization of the a-PbIxBr2-x film through the removal of coordinated CPH from the a-PbIxBr2-x network, accompanied by the formation of grain boundaries, voids, and surface roughness.The diffusion of FAIxBr1-x into the voids and/or grain boundaries resulted in the simultaneous formation of large amounts of free volume and an increase in the film thickness, resulting in a decrease in the refractive index. The red-shift of absorption edge from 3.4 to 1.73 eV is attributed to a phase transition from 0D to 3D [PbX6]4- octahedral clusters. These processes contribute synergistically to the growth of the perovskite structure.

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