TY - JOUR
T1 - Open-Circuit Voltage in Organic Solar Cells: The Impacts of Donor Semicrystallinity and Coexistence of Multiple Interfacial Charge-Transfer Bands
AU - Ngongang Ndjawa, Guy Olivier
AU - Graham, Kenneth
AU - Mollinger, Sonya
AU - Wu, Di M.
AU - Hanifi, David
AU - Prasanna, Rohit
AU - Rose, Bradley Daniel
AU - Dey, Sukumar
AU - Yu, Liyang
AU - Bredas, Jean-Luc
AU - McGehee, Michael D.
AU - Salleo, Alberto
AU - Amassian, Aram
N1 - KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The 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.
PY - 2017/1/16
Y1 - 2017/1/16
N2 - In 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 .
AB - In 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 .
UR - http://hdl.handle.net/10754/623882
UR - http://onlinelibrary.wiley.com/doi/10.1002/aenm.201601995/full
UR - http://www.scopus.com/inward/record.url?scp=85009926790&partnerID=8YFLogxK
U2 - 10.1002/aenm.201601995
DO - 10.1002/aenm.201601995
M3 - Article
SN - 1614-6832
VL - 7
SP - 1601995
JO - Advanced Energy Materials
JF - Advanced Energy Materials
IS - 12
ER -