Open-Circuit Voltage in Organic Solar Cells: The Impacts of Donor Semicrystallinity and Coexistence of Multiple Interfacial Charge-Transfer Bands
AuthorsNgongang Ndjawa, Guy Olivier
Wu, Di M.
Rose, Bradley Daniel
McGehee, Michael D.
KAUST DepartmentKAUST Solar Center (KSC)
Laboratory for Computational and Theoretical Chemistry of Advanced Materials
Material Science and Engineering Program
Organic Electronics and Photovoltaics Group
Physical Science and Engineering (PSE) Division
Online Publication Date2017-01-16
Print Publication Date2017-06
Permanent link to this recordhttp://hdl.handle.net/10754/623882
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AbstractIn organic solar cells (OSCs), the energy of the charge-transfer (CT) complexes at the donor-acceptor interface, E , determines the maximum open-circuit voltage (V ). The coexistence of phases with different degrees of order in the donor or the acceptor, as in blends of semi-crystalline donors and fullerenes in bulk heterojunction layers, influences the distribution of CT states and the V enormously. Yet, the question of how structural heterogeneities alter CT states and the V is seldom addressed systematically. In this work, we combine experimental measurements of vacuum-deposited rubrene/C bilayer OSCs, with varying microstructure and texture, with density functional theory calculations to determine how relative molecular orientations and extents of structural order influence E and V . We find that varying the microstructure of rubrene gives rise to CT bands with varying energies. The CT band that originates from crystalline rubrene lies up to ≈0.4 eV lower in energy compared to the one that arises from amorphous rubrene. These low-lying CT states contribute strongly to V losses and result mainly from hole delocalization in aggregated rubrene. This work points to the importance of realizing interfacial structural control that prevents the formation of low E configurations and maximizes V .
CitationNdjawa GON, Graham KR, Mollinger S, Wu DM, Hanifi D, et al. (2017) Open-Circuit Voltage in Organic Solar Cells: The Impacts of Donor Semicrystallinity and Coexistence of Multiple Interfacial Charge-Transfer Bands. Advanced Energy Materials: 1601995. Available: http://dx.doi.org/10.1002/aenm.201601995.
SponsorsThe Office of Competitive Research Funds at the King Abdullah University of Science and Technology supported this work in part under the CRG-3 program (A.A. and J.-L.B.). J.-L.B. acknowledges support in part from the Office of Naval Research–Global under Award No. N62909-15-1-2003. This work was also supported in part by the ONR Award Nos. N00014-14-1-0580 and N00014-16-1-2520. Portions of this work were done at the Cornell High Energy Synchrotron Source (CHESS). G.O.N.N., K.R.G., M.D.M., and A.A. acknowledge the Office of Competitive Research Funds for a GRP-CF award. K.R.G. and A.A. acknowledge SABIC for a postdoctoral fellowship. A.A. acknowledges SABIC for the Career Development SABIC Chair. The authors thank Dr. Detlef-M. Smilgies for help with acquisition of GIWAXS data at CHESS. CHESS was supported by the NSF & NIH/NIGMS via NSF Award No. DMR-1332208. The authors also acknowledge Dr. Sean Ryno for helpful discussions. Figure 3 was updated on January 17, 2017 to remove a formatting error. The scientific content was not changed.
JournalAdvanced Energy Materials