期刊
ADVANCED ENERGY MATERIALS
卷 7, 期 12, 页码 -出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/aenm.201601995
关键词
charge-transfer states; open-circuit voltage; organic photovoltaics; semicrystalline donor; small molecule organic solar cells
类别
资金
- Office of Competitive Research Funds at the King Abdullah University of Science and Technology under CRG-3 program
- Office of Naval Research-Global [N62909-15-1-2003]
- ONR Award [N00014-14-1-0580, N00014-16-1-2520]
- Office of Competitive Research Funds for GRP-CF award
- SABIC
- NSF
- NIH/NIGMS via NSF Award [DMR-1332208]
In organic solar cells (OSCs), the energy of the charge-transfer (CT) complexes at the donor-acceptor interface, E-CT, determines the maximum open-circuit voltage (V-OC). 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-OC enormously. Yet, the question of how structural heterogeneities alter CT states and the V-OC is seldom addressed systematically. In this work, we combine experimental measurements of vacuum-deposited rubrene/C-60 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-CT and V-OC. 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 approximate 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-OC 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-CT configurations and maximizes V-OC.
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