2020
DOI: 10.1021/acs.jpcc.0c05114
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Implications of Trap-Assisted Nongeminate Charge Recombination on Time- and Frequency-Domain Photocurrent Degradation Signatures of Organic Solar Cells

Abstract: Charge transport and collection in organic solar cells are heavily influenced by traps which ultimately limit the ability to harvest all photogenerated carriers. We investigate photocurrent responses of organic solar cells subjected to varying degrees of aging from time-and frequency-domain perspectives. Intensitymodulated photocurrent spectroscopy (IMPS) is primarily used here to resolve the effect of trap-assisted nongeminate charge recombination over a broad frequency range (e.g., ∼1 mHz−1 MHz). We use a co… Show more

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Cited by 4 publications
(9 citation statements)
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“…42,56 To gain further insight into the charge transport and trapassisted recombination processes in fresh and aged devices, intensity-modulated photocurrent spectroscopy (IMPS) measurements were performed. 57,58 Contrary to the IS, in IMPS, light intensity modulation at reference frequency (500 Hz−50 kHz) generates (ac) steady-state photocurrent. 57 Figure 7 shows the photocurrent response I ph (ω) of the fresh devices and devices exposed to different accelerated aging conditions for 120 h. The photocurrent response in general consists of three regions: a low-frequency region in which I ph (ω) is nearly independent of frequency, after which I ph (ω) starts increasing with frequency and reaches a distinct maximum of I max at a frequency ω max followed by a rapid decrease at a high frequency beyond the distinct maxima.…”
Section: Experimental Methodsmentioning
confidence: 99%
“…42,56 To gain further insight into the charge transport and trapassisted recombination processes in fresh and aged devices, intensity-modulated photocurrent spectroscopy (IMPS) measurements were performed. 57,58 Contrary to the IS, in IMPS, light intensity modulation at reference frequency (500 Hz−50 kHz) generates (ac) steady-state photocurrent. 57 Figure 7 shows the photocurrent response I ph (ω) of the fresh devices and devices exposed to different accelerated aging conditions for 120 h. The photocurrent response in general consists of three regions: a low-frequency region in which I ph (ω) is nearly independent of frequency, after which I ph (ω) starts increasing with frequency and reaches a distinct maximum of I max at a frequency ω max followed by a rapid decrease at a high frequency beyond the distinct maxima.…”
Section: Experimental Methodsmentioning
confidence: 99%
“…The large increase in ΔRe[Pc] at higher modulation frequencies is indicative of the relative amounts of carriers shelved in traps that are subsequently re-emitted and collected. 37 The trends in photocurrent contrast with aging duration are consistent with expected trap contributions and kinetics 37,50 though direct estimates of densities are not possible solely with IMPS. The Bode plot of Im[Pc] also shows significant changes in behavior compared to pristine and lightly aged devices where a larger positive-valued component emerges at lower modulation frequencies.…”
Section: ■ Results and Discussionmentioning
confidence: 63%
“…The large increase in ΔRe­[Pc] at higher modulation frequencies is indicative of the relative amounts of carriers shelved in traps that are subsequently re-emitted and collected . The trends in photocurrent contrast with aging duration are consistent with expected trap contributions and kinetics , though direct estimates of densities are not possible solely with IMPS.…”
Section: Resultsmentioning
confidence: 73%
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