Fabrication of FA1-xCsxPbI3 perovskite thin films using a two-step method and its application to planar structure solar cells
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 015
Publication date: 7th November 2016

 FA1-xCsxPbI3 with a mixed cation of Formamidinium (FA) and Cs system resulted in phase stabilization and showed better stability for moisture and performance compared to other systems such as CH3NH3PbI3, FAPbI3.Two-step sequential processcan fabricate well covered and uniform perovskite layer compared to the one-step solution process without anti-solvent washing. However, ionic radius of the FA+(253 pm) is larger than of CH3NH3+(217 pm), and perovskite formation rate of PbI2 film and FAI solution is slower than of PbI2 and CH3NH3I. This finding suggests that insufficient conversion of PbI2 or uncontrolled surface roughness with long reaction times are likely to occur in the case of a planar structure.However, the simple planar structure is more desirable for low cost and high throughput manufacturing processes.

 We have investigated the fabrication process of organic-inorganic perovskite FA1-xCsxPbI3 thin films on compact TiO2 layers by the reaction of porous PbI2·CsIx layers and high concentration FAI solution. The fabricated FA1-xCsxPbI3thin films were characterized by XRD, UV-Vis absorption, PL,FESEM, and AFM. When x was increased, the δ phase and PbI2 disappeared with a significant improvement in crystallinity, and the absorption band edge shifted to shorter wavelengths with x=0 to 0.2 and when x=0.3, CsPbI3 was formed.The fabricated perovskite thin films have dense and pore-free surfaces with minimal surface roughness and the fabricated FA1-xCsxPbIthin films were applied to the planar structure solar cells(Glass/FTO/TiO2/Perovskite/spiro-OMeTAD/Ag). when x = 0.2 among x = 0 to 0.3, a PCE was highest at 14.7% with JSC of 21.4 mA cm-2, VOC of 1.02 V and FF of 67.5 % in reverse scan.

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