TY - JOUR
T1 - Deciphering the metal-C60 interface in optoelectronic devices
T2 - Evidence for C60 reduction by vapor deposited Al
AU - Matz, Dallas L.
AU - Ratcliff, Erin L.
AU - Meyer, Jens
AU - Kahn, Antoine
AU - Pemberton, Jeanne E.
PY - 2013/7/10
Y1 - 2013/7/10
N2 - The formation of interfacial midgap states due to the reduction of buckminsterfullerene (C60) to amorphous carbon upon subsequent vapor deposition of Al is confirmed using Raman spectroscopy and X-ray, ultraviolet, and inverse photoemission spectroscopies. We demonstrate that vapor deposition of Al results in n-type doping of C60 due to an electron transfer from Al to the LUMO of C60, resulting in the formation of midgap states near the C60 Fermi level. Raman spectroscopy in ultrahigh vacuum clearly identifies the presence of the C60 anion radical (C60•-) as well as amorphous carbon created by further degradation of C60•-. In contrast, the interface formed by vapor deposition of Ag shows only a slight Ag/C60 interfacial charge displacement with no evidence for complete metal-to-C 60 electron transfer to form the anion radical or its further degradation products. These results confirm previous speculations of metal-induced chemical damage of C60 films after Al deposition, which is widely suspected of decreasing charge collection efficiency in OPVs, and provide key insight into charge collection at metal/organic interfaces in such devices.
AB - The formation of interfacial midgap states due to the reduction of buckminsterfullerene (C60) to amorphous carbon upon subsequent vapor deposition of Al is confirmed using Raman spectroscopy and X-ray, ultraviolet, and inverse photoemission spectroscopies. We demonstrate that vapor deposition of Al results in n-type doping of C60 due to an electron transfer from Al to the LUMO of C60, resulting in the formation of midgap states near the C60 Fermi level. Raman spectroscopy in ultrahigh vacuum clearly identifies the presence of the C60 anion radical (C60•-) as well as amorphous carbon created by further degradation of C60•-. In contrast, the interface formed by vapor deposition of Ag shows only a slight Ag/C60 interfacial charge displacement with no evidence for complete metal-to-C 60 electron transfer to form the anion radical or its further degradation products. These results confirm previous speculations of metal-induced chemical damage of C60 films after Al deposition, which is widely suspected of decreasing charge collection efficiency in OPVs, and provide key insight into charge collection at metal/organic interfaces in such devices.
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U2 - 10.1021/am400640x
DO - 10.1021/am400640x
M3 - Article
C2 - 23734813
AN - SCOPUS:84880076089
SN - 1944-8244
VL - 5
SP - 6001
EP - 6008
JO - ACS Applied Materials and Interfaces
JF - ACS Applied Materials and Interfaces
IS - 13
ER -