Abstract
Organic solar cells (OSCs) using non-fullerene acceptors (NFAs) afford exceptional photovoltaic performance metrics, however, their stability remains a significant challenge. Existing OSC stability studies focus on understanding degradation rate-performance relationships, improving interfacial layers, and suppressing degradative chemical reaction pathways. Nevertheless, there is a knowledge gap concerning how such degradation affects crystal structure, electronic states, and recombination dynamics that ultimately impact NFA performance. Here we seek a quantitative relationship between OSC metrics and blend morphology, trap density of states, charge carrier mobility, and recombination processes during the UV-light-induced degradation of PBDB-TF:Y6 inverted solar cells as the PCE (power conversion efficiency) falls from 17.3 to 5.0%. Temperature-dependent electrical and impedance measurements reveal deep traps at 0.48 eV below the conduction band that are unaffected by Y6 degradation, and shallow traps at 0.15 eV below the conduction band that undergo a three-fold density of states increase at the PCE degradation onset. Computational analysis correlates vinyl oxidation with a new trap state at 0.25 eV below the conduction band, likely involving charge transfer from the UV-absorbing ZnO electron transport layer. In situ integrated photocurrent analysis and transient absorption spectroscopy reveal that these traps lower electron mobility and increase recombination rates during degradation. Grazing-incidence wide-angle X-ray scattering and computational analysis reveal that the degraded Y6 crystallite morphology is largely preserved but that <1% of degraded Y6 molecules cause OSC PCE performance degradation by ≈50%. Together the detailed electrical, impedance, morphological, ultrafast spectroscopic, matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) spectroscopy, and computational data reveal that the trap state energies and densities accompanying Y6 vinyl oxidation are primarily responsible for the PCE degradation in these operating NFA-OSCs.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 21213-21229 |
| Number of pages | 17 |
| Journal | Journal of Materials Chemistry A |
| Volume | 12 |
| Issue number | 32 |
| DOIs | |
| State | Published - Jul 9 2024 |
Funding
This work was supported by U.S. Office of Naval Research Contracts #No. N00014-20-1-2116 and N00014-24-1-2109 (G. L.: material synthesis and characterizations), by the U.S. Department of Commerce, National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design Award #70NANB19H005, and by the Northwestern University Materials Research Science and Engineering Center Award NSF DMR-2308691 (V. K. S., Z. M.: charge transport measurements). This work (IVT, TAS, and IPDA) made use of the MatCI Facility which receives support from the MRSEC Program (NSF DMR-2308691) of the Materials Research Center at Northwestern University. Transient optical spectroscopy was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award DE-FG02-99ER14999 (MRW). Theory work (G. C. S.) was supported by NSF Grant CHE-2347622. This work made use of the GIANTFab core facility at Northwestern University. GIANTFab is supported by the Institute for Sustainability and Energy at Northwestern and the Office of the Vice President for Research at Northwestern. R. M. P. acknowledges support from the Intelligence Community Postdoctoral Research Fellowship Program at Northwestern University administered by Oak Ridge Institute for Science and Education (ORISE) through an interagency agreement between the U.S. Department of Energy and the Office of the Director of National Intelligence (ODNI). This work made use of the IMSERC MS facility at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-2025633), the State of Illinois, and the International Institute for Nanotechnology (IIN). The computational resource was supported by Northwestern\u2019s Quest High-Performance Computing Cluster. This work also acknowledges the U.S. Department of Energy under contract no. DE-AC02-05CH11231 at the beamline 8-ID-E of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.
ASJC Scopus subject areas
- General Chemistry
- Renewable Energy, Sustainability and the Environment
- General Materials Science
