TY - JOUR
T1 - Correlation of open-circuit voltage and energy levels in zinc-phthalocyanine
T2 - C60 bulk heterojunction solar cells with varied mixing ratio
AU - Tietze, Max L.
AU - Tress, Wolfgang
AU - Pfützner, Steffen
AU - Schünemann, Christoph
AU - Burtone, Lorenzo
AU - Riede, Moritz
AU - Leo, Karl
AU - Vandewal, Koen
AU - Olthof, Selina
AU - Schulz, Philip
AU - Kahn, Antoine
PY - 2013/8/20
Y1 - 2013/8/20
N2 - The maximum open-circuit voltage VOC of bulk-heterojunction solar cells is limited by the effective HOMO(donor)-LUMO(acceptor) gap of the photoactive absorber blend. We investigate blend layers comprising zinc-phthalocyanine (ZnPc) and the buckminster fullerene C60 with ultraviolet, x-ray, and inverse photoelectron spectroscopy. By varying the volume mixing ratio ZnPc:C60 from 6:1 to 1:6, we observe a linear increase of the HOMO(ZnPc)-LUMO(C60) gap by 0.25 eV. The trend in this gap correlates with the change in the charge transfer energy measured by Fourier-transform photocurrent spectroscopy as well as with the observed open-circuit voltage of solar cells containing ZnPc:C60 as the photoactive absorber layer. Furthermore, the morphology of different ZnPc:C 60 blend layers is investigated by grazing-incidence x-ray diffraction. As physical origins for the changed energy levels, a suppressed crystallization of the C60 phase in the presence of donor molecules as well as concentration-dependent growth modes of the ZnPc phase are suggested.
AB - The maximum open-circuit voltage VOC of bulk-heterojunction solar cells is limited by the effective HOMO(donor)-LUMO(acceptor) gap of the photoactive absorber blend. We investigate blend layers comprising zinc-phthalocyanine (ZnPc) and the buckminster fullerene C60 with ultraviolet, x-ray, and inverse photoelectron spectroscopy. By varying the volume mixing ratio ZnPc:C60 from 6:1 to 1:6, we observe a linear increase of the HOMO(ZnPc)-LUMO(C60) gap by 0.25 eV. The trend in this gap correlates with the change in the charge transfer energy measured by Fourier-transform photocurrent spectroscopy as well as with the observed open-circuit voltage of solar cells containing ZnPc:C60 as the photoactive absorber layer. Furthermore, the morphology of different ZnPc:C 60 blend layers is investigated by grazing-incidence x-ray diffraction. As physical origins for the changed energy levels, a suppressed crystallization of the C60 phase in the presence of donor molecules as well as concentration-dependent growth modes of the ZnPc phase are suggested.
UR - https://www.scopus.com/pages/publications/84884569730
UR - https://www.scopus.com/pages/publications/84884569730#tab=citedBy
U2 - 10.1103/PhysRevB.88.085119
DO - 10.1103/PhysRevB.88.085119
M3 - Article
AN - SCOPUS:84884569730
SN - 1098-0121
VL - 88
JO - Physical Review B - Condensed Matter and Materials Physics
JF - Physical Review B - Condensed Matter and Materials Physics
IS - 8
M1 - 085119
ER -