Fabrication of Highly Efficient Perovskite Solar Cells: Properties of Key Intermediates in Solution Process
Yumi Nakaike a, Tomoko Aharen a, Takahiro Sasamori a, Norihiro Tokitoh a, Yasujiro Murata a, Naoki Maruyama a, Ai Shimazaki a, Masashi Ozaki a, Alwani Rafieh a, Mina Jung a, Atsushi Wakamiya a
a Kyoto university, 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, Mina Jung, 017
Publication date: 7th November 2016

Perovskite solar cells using methyl ammonium lead triiodide (CH3NH3PbI3) perovskite as a photoabsorber have attracted much attention as promising next-generation highly efficient solar cells. The performance of perovskite solar cells is known to highly depend on the quality of the perovskite layer. Among several methods for fabrication of perovskite layer, we focused on a one-step solution method, in which perovskite film is formed by spin-coating a mixed solution of CH3NH3I and PbI2 in DMSO or DMF with toluene treatment, followed by annealing. In this process, the transparent film is formed after spin-coating, which immediately colorizes to black corresponding to perovskite upon annealing at ~100 ℃. We focused on transparent intermediate and succeeded in isolation of these crystals. X-ray structural analysis revealed that the intermediate crystals prepared from DMSO or DMF solution correspond to MA2Pb3I8∙2DMSO or MA2Pb3I8∙2DMF as composition formula, respectively, both of which contain intercalated solvent molecules. Thermogravimetric analysis on these crystals indicates that the intercalated solvent molecules come out from the intermediate at ~78 ℃ to become black solids. Based on these characteristics of the intermediates, we optimized our device fabrication method to achieve high power conversion efficiency (~20.3%) with high reproducibility, even in the cells using a pure CH3NH3PbI3 perovskite photoabsorber. In this presentation, the details of the properties of the intermediates as well as our fabrication process will be introduced. 

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