期刊
JOURNAL OF PHYSICAL CHEMISTRY C
卷 116, 期 50, 页码 26300-26305出版社
AMER CHEMICAL SOC
DOI: 10.1021/jp306433g
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资金
- Swedish Research Council (VR)
- Goran Gustafsson Foundation
- Carl Trygger Foundation
- Swedish Energy Agency
- European Community [226716]
Hard X-ray photoelectron spectroscopy (HAXPES) has been used to study the effects of adding Li-TFSI to hole conducting molecular thin films of 2,2',7,7'-tetrakis(N,N'-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD). The work shows that a procedure of mixing a Li-TFSI solution into a spiro-OMeTAD solution, and subsequent spin-coating this mixture into a solid thin film causes the Fermi level of the molecular film to move closer to the HOMO level. Hence, adding the Li-TFSI gives similar effects to spiro-OMeTAD as a p-dopant. Specific effects from doping on the valence levels were also characterized. Absorbance measurements also showed that the spiro-OMeTAD film was partially oxidized when Li-TFSI was added before spin-coating. By varying the photon energy in the photoelectron spectroscopy measurements, the probe depth varies between being surface sensitive (<1 nm) and bulk sensitive (inelastic mean free path >= 10 nm). This property was used to follow differences in the composition at different depth of the spiro-OMeTAD/Li-TFSI film. It could be concluded that there was a concentration gradient in the molecular film and that the concentration of Li-TFSI was dominating at the interface between the spiro-OMeTAD/Li-TFSI film and vacuum.
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