Correlation of open-circuit voltage and energy levels in zinc-phthalocyanine: C60bulk heterojunction solar cells with varied mixing ratio
| Autor: | Moritz Riede, Selina Olthof, Antoine Kahn, Max L. Tietze, Karl Leo, Christoph Schünemann, Philip Schulz, Koen Vandewal, Lorenzo Burtone, Steffen Pfützner, Wolfgang Tress |
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| Rok vydání: | 2013 |
| Předmět: | |
| Zdroj: | Physical Review B. 88 |
| ISSN: | 1550-235X 1098-0121 |
| Popis: | The maximum open-circuit voltage ${V}_{\mathrm{OC}}$ 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 ${\mathrm{C}}_{60}$ with ultraviolet, x-ray, and inverse photoelectron spectroscopy. By varying the volume mixing ratio ZnPc:${\mathrm{C}}_{60}$ from 6:1 to 1:6, we observe a linear increase of the HOMO(ZnPc)-LUMO(${\mathrm{C}}_{60}$) 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:${\mathrm{C}}_{60}$ as the photoactive absorber layer. Furthermore, the morphology of different ZnPc:${\mathrm{C}}_{60}$ blend layers is investigated by grazing-incidence x-ray diffraction. As physical origins for the changed energy levels, a suppressed crystallization of the ${\mathrm{C}}_{60}$ phase in the presence of donor molecules as well as concentration-dependent growth modes of the ZnPc phase are suggested. |
| Databáze: | OpenAIRE |
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