TY - JOUR
T1 - Charge Carrier Generation Followed by Triplet State Formation, Annihilation, and Carrier Recreation in PBDTTT-C:PC 60 BM Photovoltaic Blends
AU - Gehrig, Dominik W.
AU - Howard, Ian A.
AU - Laquai, Frédéric
N1 - KAUST Repository Item: Exported on 2020-10-01
PY - 2015/6/5
Y1 - 2015/6/5
N2 - Triplet state formation after photoexcitation of low-bandgap polymer:fullerene blends has recently been demonstrated, however, the precise mechanism and its impact on solar cell performance is still under debate. Here, we study exciton dissociation, charge carrier generation and triplet state formation in low-bandgap polymer PBDTTT-C:PC60BM bulk heterojunction photovoltaic blends by a combination of fs-µs broadband Vis-NIR transient absorption (TA) pump-probe spectroscopy and multivariate curve resolution (MCR) data analysis. We found sub-ps exciton dissociation and charge generation followed by sub-ns triplet state creation. The carrier dynamics and triplet state dynamics exhibited a very pronounced intensity dependence indicating non-geminate recombination of free carriers is the origin of triplet formation in these blends. Triplets were found to be the dominant state present on the nanosecond timescale. Surprisingly, the carrier population increased again on the ns-µs timescale. We attribute this to triplet-triplet annihilation and the formation of higher energy excited states that subsequently underwent charge transfer. This unique dip and recovery of the charge population is a clear indication that triplets are formed by non-geminate recombination, as such a kinetic is incompatible with a monomolecular triplet state formation process.
AB - Triplet state formation after photoexcitation of low-bandgap polymer:fullerene blends has recently been demonstrated, however, the precise mechanism and its impact on solar cell performance is still under debate. Here, we study exciton dissociation, charge carrier generation and triplet state formation in low-bandgap polymer PBDTTT-C:PC60BM bulk heterojunction photovoltaic blends by a combination of fs-µs broadband Vis-NIR transient absorption (TA) pump-probe spectroscopy and multivariate curve resolution (MCR) data analysis. We found sub-ps exciton dissociation and charge generation followed by sub-ns triplet state creation. The carrier dynamics and triplet state dynamics exhibited a very pronounced intensity dependence indicating non-geminate recombination of free carriers is the origin of triplet formation in these blends. Triplets were found to be the dominant state present on the nanosecond timescale. Surprisingly, the carrier population increased again on the ns-µs timescale. We attribute this to triplet-triplet annihilation and the formation of higher energy excited states that subsequently underwent charge transfer. This unique dip and recovery of the charge population is a clear indication that triplets are formed by non-geminate recombination, as such a kinetic is incompatible with a monomolecular triplet state formation process.
UR - http://hdl.handle.net/10754/555636
UR - http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.5b03467
UR - http://www.scopus.com/inward/record.url?scp=84935016251&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcc.5b03467
DO - 10.1021/acs.jpcc.5b03467
M3 - Article
SN - 1932-7447
VL - 119
SP - 13509
EP - 13515
JO - The Journal of Physical Chemistry C
JF - The Journal of Physical Chemistry C
IS - 24
ER -