Air-Exposure Induced Dopant Redistribution and Energy Level Shifts in Spin-Coated Spiro-MeOTAD Films

作者：Hawash, Zafer; Ono, Luis K.; Raga, Sonia R.; Lee, Michael V.; Qi, Yabing^*

来源：Chemistry of Materials, 2015, 27(2): 562-569.

DOI：10.1021/cm504022q

• HYBRID SOLAR-CELLS
• LITHIUM-SALTS
• ORGANIC SEMICONDUCTORS
• DYE
• PEROVSKITE
• OMETAD
• DEVICE
• TIO2
• PERFORMANCE
• STABILITY

Doping properties of 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-MeOTAD) hole transport layer are investigated by X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and atomic force microscopy under air exposure. XPS results reveal that 3 h exposure of Li-bis(trifluoromethanesulfonyl)-imide (LiTFSI) doped spiro-MeOTAD to air results in the migration of LiTFSI from the bottom to the top across the spiro-MeOTAD film. AFM images reveal the presence of pinholes with an average diameter of similar to 135 nm and a density of similar to 3.72 holes/mu m(2). In addition, cross-sectional scanning electron microscope images reveal that these pinholes form channels across the doped spiro-MeOTAD film. Optical microscopy and Fourier transform infrared microscopy images confirm the presence of large pinholes with diameters in the range of 1-20 mu m and a density of similar to 289 holes/mm(2) as well. The presence of 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.

• 出版日期2015-1-27