title: Excitation Intensity Dependent Carrier Dynamics of Chalcogen Heteroatoms in Medium-Bandgap Polymer Solar Cells.
abstract: The excitation intensity dependent carrier dynamics of blends with PC[70]BM of three new medium-band gap conjugated polymers with central chalcogen heteroatoms, PBDTfDTBX (X = O, T(Sulphur), Se) were studied. The PBDTfDTBX polymers (Poly[4,8-bis(5-(2-butyloctyl)thiophene-2-yl)benzo[1,2-b;4,5-b']dithiophene-alt-4,7-bis(4-(2-ethylhexyl)-2-thienyl)-dithieno[3',2':3,4;2″,3″:5,6]benzo[1,2-c][1,2,5] furazan or thiadiazole or selenadiazole]) have symmetrical structures but exhibit different solar cell performances. In this study, we determined how the photogenerated charge carrrier dynamics of the PBDTfDTBX:PC[70]BM blends varies with the heteroatom by performing transient absorption measurements at various excitation intensities. It was found that the charge carrier dynamics of the PBDTfDTBX blends with X = T or Se heteroatoms are dependent on the excitation intensity whereas that of the PBDTfDTBO blend is independent of the intensity. The photogenerated charge carrier dynamics of the PBDTfDTBO:PCBM, PBDTfDTBT:PCBM, and PBDTfDTBSe:PCBM blends were all modeled globally and rates were estimated for different photophysical processes occurring on different time scales.
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 37673, Korea.
authors.forename: Chandramouli
authors.initials: C
authors.lastname: Kulshreshtha
authors.affiliation: Department of Chemistry, Pohang University of Science and Technology, Pohang, 37673, Korea.
authors.forename: Jiwon
authors.initials: J
authors.lastname: Son
authors.affiliation: Chemical Physics, Kemicentrum, Lund University, SE-22100, Lund, Sweden.
authors.forename: Torbjörn
authors.initials: T
authors.lastname: Pascher
authors.affiliation: Department of Energy Science, Sungkyunkwan University, Suwon, Korea.
authors.forename: Ji-Hee
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Department of Chemistry, Pohang University of Science and Technology, Pohang, 37673, Korea.
authors.forename: Taiha
authors.initials: T
authors.lastname: Joo
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 37673, Korea.
authors.forename: Jaewon
authors.initials: J
authors.lastname: Lee
authors.affiliation: Department of Energy Science, Sungkyunkwan University, Suwon, Korea.
authors.forename: Mun Seok
authors.initials: MS
authors.lastname: Jeong
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 37673, Korea. kwcho@postech.ac.kr.
authors.forename: Kilwon
authors.initials: K
authors.lastname: Cho