Optical studies of native defects in π-conjugated donor–acceptor copolymers

Baniya, Sangita; Khanal, Dipak Raj; Lafalce, Evan; You, Wei; Vardeny, Z. Valy

doi:10.1063/1.5012995

Cited by 3 publications

(4 citation statements)

References 45 publications

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“…This is used to demonstrate the presence of unexpected ABBA defects in the C 14 DPPF-F copolymer and to quantify their occurrence. The existence of excitonic and electronic trap states in a conjugated polymer backbone has long been discussed, and their origin has often been loosely described as impurities in the form of morphological or chemical defects ( 24 , 25 ). Little was known about the nature and the frequency of defects, although it has always been assumed that they were either torsional defects along the backbone—for example, hairpins ( 26 )—or chemical defects—such as homo- or mis-couplings ( 27 , 28 ).…”

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Sequencing conjugated polymers by eye

et al. 2018

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Sequencing conjugated polymers by eye

et al. 2018

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“…This is in agreement with the previous report of E b = 0.56 eV for FTAZ reported by S. Baniya, et al using the same method. [83] More details about EAS measurements and simulation can be found in Section S8 (Supporting Information). The ground state (S 0 ) and first electronic excited state (S 1 ) potentials are presented with two displaced harmonic potential (by ΔQ) in configuration coordinates.…”

Section: Resultsmentioning

confidence: 99%

“…using the same method. [ 83 ] More details about EAS measurements and simulation can be found in Section S8 (Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

Exciton Binding Energy in Organic Polymers: Experimental Considerations and Tuning Prospects

Kashani,

Rech,

Liu

et al. 2023

Advanced Energy Materials

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Discrepancies in reported values of exciton binding energy (Eb) for organic semiconductors (OSs) necessitate a comprehensive study. Traditionally, Eb is defined as the difference between the transport gap (Et) and the optical gap (Eopt). Here, the Eb values of PBnDT‐TAZ polymer variants are determined using two commonly employed methods: a combination of ultraviolet photoemission spectroscopy and low‐energy inverse photoemission spectroscopy (UPS‐LEIPS) and solid‐state cyclic voltammetry (CV). Eb values obtained by UPS‐LEIPS show low dispersion and no clear correlation with the polymer structure and thedielectric properties. In contrast, CV reveals a larger dispersion (200 meV‐1 eV) and an apparent qualitative Eb‐molecular structure correlation, as the lowest Eb values are observed for oligo‐ethylene glycol side chains. This discrepancy is discussed by examining the implications of the traditional definition of Eb. Additionally, the impact of both intrinsic and extrinsic factors contributing to the derived experimental values of Et is discussed. The differences in intrinsic and extrinsic factors highlight the context‐dependent nature of measurement when drawing global conclusions. Notably, the observed Eb trend derived from CV is not intrinsic to the pure materials but likely linked to electrolyte swelling and associated changes in dielectric environment, suggesting that high‐efficiency single‐material organic photovoltaics with low Eb may be possible via high dielectric materials.

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Studies of photoexcitations in polymer/non-fullerene blend for high-efficiency organic solar cells

Khanal

Lafalce

Vardeny

2021

Applied Physics Letters

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We studied the photoexcitations properties in the blend of PBDB-T-SF, a donor π-conjugated copolymer, and ITIC-2F, a non-fullerene acceptor molecule, which is used as an active layer in high-performance organic photovoltaic (OPV) solar cells. We used several steady-state spectroscopies such as photoinduced absorption (PIA), photoluminescence (PL), magneto-photoinduced absorption (MPA), and magneto-PL in the pristine and blend films. The PIA spectra of the pristine copolymer and acceptor films contain a photoinduced absorption (PA) band due to triplet excitons, which is confirmed by the MPA(B) response, whereas the PIA spectrum of the copolymer/molecule blend contains several PA bands due to polaron pairs at the copolymer chain/molecule interfaces. Interestingly, when exciting the PIA spectrum of the blend at two different photon energies, namely, ℏω≈2.39 eV that preferentially excites the copolymer chains and ℏω≈1.58 eV that excites only the acceptor molecules, we found that the PIA spectra are the same. This shows that charge photogeneration is possible when exciting either the copolymer chains or the acceptor molecules, which might explain the high power conversion efficiency of OPV cells based on this blend. We also found from the MPA(B) responses of the pristine copolymer and acceptor films and their blend that the back reaction of the photogenerated polaron pairs into the copolymer forming triplet excitons is absent, further explaining the high power conversion efficiency of this blend as the active layer in OPV solar cells.

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Optical studies of native defects in π-conjugated donor–acceptor copolymers

Cited by 3 publications

References 45 publications

Sequencing conjugated polymers by eye

Sequencing conjugated polymers by eye

Exciton Binding Energy in Organic Polymers: Experimental Considerations and Tuning Prospects

Studies of photoexcitations in polymer/non-fullerene blend for high-efficiency organic solar cells

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