Unique Degradation Signatures of Organic Solar Cells with Nonfullerene Electron Acceptors
Chemical Sciences not elsewhere classified
device optimization strategies
NFA
Biophysics
8DFIC
02 engineering and technology
Microbiology
7. Clean energy
k rec values
Unique Degradation Signatures
Space Science
device contact interfaces
Nonfullerene Electron Acceptors
Molecular Biology
degradation trends
density
Organic Solar Cells
excitation intensity
NIR
trap densities
contrast
display
recombination
PTB
quadrant IMPS component
intensity-modulated photocurrent sp.
Medicine
0210 nano-technology
Physical Sciences not elsewhere classified
performance
Biotechnology
Developmental Biology
Biological Sciences not elsewhere classified
DOI:
10.1021/acsami.0c21367
Publication Date:
2021-01-23T04:56:11Z
AUTHORS (3)
ABSTRACT
We investigate the degradation phenomena of organic solar cells based on nonfullerene electron acceptors (NFA) using intensity-modulated photocurrent spectroscopy (IMPS). Devices composed of NIR absorbing blends of a polymer (PTB7) and NFA molecules (COi8DFIC) were operated in air for varying periods of time that display unusual degradation trends. Light aging (e.g., ∼3 days) results in a characteristic first quadrant (positive phase shifts) degradation feature in IMPS Nyquist (Bode) plots that grow in amplitude and frequency with increasing excitation intensity and then subsequently turns over and vanishes. By contrast, devices aged and operated in air for longer times (>5 days) display poor photovoltaic performance and have a dominant first quadrant IMPS component that grows nonlinearly with excitation intensity. We analyze these degradation trends using a simple model with descriptors underlying the first quadrant feature (i.e., trap lifetime and occupancy). The results indicate that the quasi first-order recombination rate constant, krec, is significantly slower in addition to lower trap densities in devices exhibiting light aging effects that are overcome by increasing carrier densities (viz. excitation intensity). By contrast, larger trap densities and distributions coupled with larger krec values are found to be responsible for the continuous growth of the first quadrant with light intensity. We believe that defect formation and charge recombination at device contact interfaces is chiefly responsible for performance degradation, which offers several directions for materials and device optimization strategies to minimize long-term detrimental factors.
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CITATIONS (2)
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