Correlation of open-circuit voltage and energy levels in zinc-phthalocyanine: Cbulk heterojunction solar cells with varied mixing ratio
- 20 August 2013
- journal article
- Published by American Physical Society (APS) in Physical Review B
- Vol. 88 (8)
- https://doi.org/10.1103/physrevb.88.085119
Abstract
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:C60 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. © 2013 American Physical SocietyKeywords
This publication has 22 references indexed in Scilit:
- Evaluation and Control of the Orientation of Small Molecules for Strongly Absorbing Organic Thin FilmsThe Journal of Physical Chemistry C, 2013
- Correlation of Absorption Profile and Fill Factor in Organic Solar Cells: The Role of Mobility ImbalanceAdvanced Energy Materials, 2013
- Influence of Fullerene Ordering on the Energy of the Charge-Transfer State and Open-Circuit Voltage in Polymer:Fullerene Solar CellsThe Journal of Physical Chemistry C, 2011
- Influence of Hole‐Transport Layers and Donor Materials on Open‐Circuit Voltage and Shape of I–V Curves of Organic Solar CellsAdvanced Functional Materials, 2011
- Temperature dependence of open-circuit voltage in organic solar cells from generation–recombination kinetic balanceSolar Energy Materials and Solar Cells, 2010
- The electronic structure of C60/ZnPc interface for organic photovoltaic device with blended layer architectureApplied Physics Letters, 2010
- Compositional and Electric Field Dependence of the Dissociation of Charge Transfer Excitons in Alternating Polyfluorene Copolymer/Fullerene BlendsJournal of the American Chemical Society, 2008
- Offset energies at organic semiconductor heterojunctions and their influence on the open-circuit voltage of thin-film solar cellsPhysical Review B, 2007
- Efficient bulk heterojunction photovoltaic cells using small-molecular-weight organic thin filmsNature, 2003
- Polymer Photovoltaic Cells: Enhanced Efficiencies via a Network of Internal Donor-Acceptor HeterojunctionsScience, 1995