The Role of Air-Exposure in Spiro-MeOTAD Films Property Changes and Perovskite Solar Cell Stability

Prof. Yabing Qi (戚亚冰)

Energy Materials and Surface Sciences Unit (EMSS)

Okinawa Institute of Science and Technology Graduate University (OIST), JAPAN地点: 物理楼中楼212室

时间： 2015年2月2日 (星期一)上午9:00-11:00

Recently perovskite-based solar cells have garnered much attention because of low-cost fabrication and high efficiency (~20%). On the other hand, the understanding about device degradation mechanisms and long-term stability remains largely elusive. In this talk, I will focus on air-exposure effects on 2,2’,7,7’-tetraakis(N,N-di-p-methoxy phenylamine)-9,9’-spirobifluorene (spiro-MeOTAD) films, the most widely used hole transport material for perovskite solar cells. In the case of neat spiro-MeOTAD films prepared by vacuum evaporation, gas molecules diffuse into spiro-MeOTAD films causing a decrease in charge mobility. In the case of Li-bis(trifluoromethanesulfonyl)-imide (LiTFSI) doped spiro-MeOTAD films prepared by spin coating, 3 hours air-exposure results in the migration of LiTFSI from the bottom to the top across the spiro-MeOTAD film. A combined microscopy study by AFM, cross sectional Scanning Electron Microscopy, optical microscopy and Fourier Transform Infrared microscopy reveals the presence of a relatively high density of pinholes that form channels across the doped spiro-MeOTAD film. These pinholes may play a major role in the migration processes of the LiTFSI within the spiro-MeOTAD film as well as on the degradation processes of solar cells. This is further confirmed by the rapid decreasing efficiency of perovskite solar cells with solution prepared doped spiro-MeOTAD layers when exposed to air.

Dr. Yabing Qi is Assistant Professor and Head of Energy Materials and Surface Sciences Unit at Okinawa Institute of Science and Technology Graduate University. Prior to his current appointment, Dr. Qi was a postdoctoral research fellow at Princeton University. He received his B.S., M.Phil., and Ph.D. from Nanjing University, Hong Kong University of Science and Technology, and University of California Berkeley, respectively. His research interests include energy materials and devices, organic electronics, surface sciences, and condensed matter physics.

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