Abstract
Exciton dissociation is a key step for the light energy conversion to electricity in organic photovoltaic (OPV) devices. Here, excitonic dissociation pathways in the high-performance, low bandgap "in-chain donor-acceptor" polymer PTB7 by transient optical absorption (TA) spectroscopy in solutions, neat films, and bulk heterojunction (BHJ) PTB7:PC71BM (phenyl-C71-butyric acid methyl ester) films are investigated. The dynamics and energetics of the exciton and intra-/intermolecular charge separated states are characterized. A distinct, dynamic, spectral red-shift of the polymer cation is observed in the BHJ films in TA spectra following electron transfer from the polymer to PC71BM, which can be attributed to the time evolution of the hole-electron spatial separation after exciton splitting. Effects of film morphology are also investigated and compared to those of conjugated homopolymers. The enhanced charge separation along the PTB7 alternating donor-acceptor backbone is understood by intramolecular charge separation through polarized, delocalized excitons that lower the exciton binding energy. Consequently, ultrafast charge separation and transport along these polymer backbones reduce carrier recombination in these largely amorphous films. This charge separation mechanism explains why higher degrees of PCBM intercalation within BHJ matrices enhances exciton splitting and charge transport, and thus increase OPV performance. This study proposes new guidelines for OPV materials development.
| Original language | English |
|---|---|
| Pages (from-to) | 10-26 |
| Number of pages | 17 |
| Journal | Advanced Functional Materials |
| Volume | 24 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - Jan 8 2014 |
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Keywords
- bulk heterojunction
- charge transfer
- conjugated polymers
- morphology
- organic photovoltaics
ASJC Scopus subject areas
- Biomaterials
- Electrochemistry
- Condensed Matter Physics
- Electronic, Optical and Magnetic Materials
Cite this
Photovoltaic function and exciton/charge transfer dynamics in a highly efficient semiconducting copolymer. / Szarko, Jodi M.; Rolczynski, Brian S.; Lou, Sylvia J.; Xu, Tao; Strzalka, Joseph; Marks, Tobin J; Yu, Luping; Chen, Lin X.
In: Advanced Functional Materials, Vol. 24, No. 1, 08.01.2014, p. 10-26.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Photovoltaic function and exciton/charge transfer dynamics in a highly efficient semiconducting copolymer
AU - Szarko, Jodi M.
AU - Rolczynski, Brian S.
AU - Lou, Sylvia J.
AU - Xu, Tao
AU - Strzalka, Joseph
AU - Marks, Tobin J
AU - Yu, Luping
AU - Chen, Lin X.
PY - 2014/1/8
Y1 - 2014/1/8
N2 - Exciton dissociation is a key step for the light energy conversion to electricity in organic photovoltaic (OPV) devices. Here, excitonic dissociation pathways in the high-performance, low bandgap "in-chain donor-acceptor" polymer PTB7 by transient optical absorption (TA) spectroscopy in solutions, neat films, and bulk heterojunction (BHJ) PTB7:PC71BM (phenyl-C71-butyric acid methyl ester) films are investigated. The dynamics and energetics of the exciton and intra-/intermolecular charge separated states are characterized. A distinct, dynamic, spectral red-shift of the polymer cation is observed in the BHJ films in TA spectra following electron transfer from the polymer to PC71BM, which can be attributed to the time evolution of the hole-electron spatial separation after exciton splitting. Effects of film morphology are also investigated and compared to those of conjugated homopolymers. The enhanced charge separation along the PTB7 alternating donor-acceptor backbone is understood by intramolecular charge separation through polarized, delocalized excitons that lower the exciton binding energy. Consequently, ultrafast charge separation and transport along these polymer backbones reduce carrier recombination in these largely amorphous films. This charge separation mechanism explains why higher degrees of PCBM intercalation within BHJ matrices enhances exciton splitting and charge transport, and thus increase OPV performance. This study proposes new guidelines for OPV materials development.
AB - Exciton dissociation is a key step for the light energy conversion to electricity in organic photovoltaic (OPV) devices. Here, excitonic dissociation pathways in the high-performance, low bandgap "in-chain donor-acceptor" polymer PTB7 by transient optical absorption (TA) spectroscopy in solutions, neat films, and bulk heterojunction (BHJ) PTB7:PC71BM (phenyl-C71-butyric acid methyl ester) films are investigated. The dynamics and energetics of the exciton and intra-/intermolecular charge separated states are characterized. A distinct, dynamic, spectral red-shift of the polymer cation is observed in the BHJ films in TA spectra following electron transfer from the polymer to PC71BM, which can be attributed to the time evolution of the hole-electron spatial separation after exciton splitting. Effects of film morphology are also investigated and compared to those of conjugated homopolymers. The enhanced charge separation along the PTB7 alternating donor-acceptor backbone is understood by intramolecular charge separation through polarized, delocalized excitons that lower the exciton binding energy. Consequently, ultrafast charge separation and transport along these polymer backbones reduce carrier recombination in these largely amorphous films. This charge separation mechanism explains why higher degrees of PCBM intercalation within BHJ matrices enhances exciton splitting and charge transport, and thus increase OPV performance. This study proposes new guidelines for OPV materials development.
KW - bulk heterojunction
KW - charge transfer
KW - conjugated polymers
KW - morphology
KW - organic photovoltaics
UR - http://www.scopus.com/inward/record.url?scp=84891558968&partnerID=8YFLogxK
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U2 - 10.1002/adfm.201301820
DO - 10.1002/adfm.201301820
M3 - Article
VL - 24
SP - 10
EP - 26
JO - Advanced Functional Materials
JF - Advanced Functional Materials
SN - 1616-301X
IS - 1
ER -