Amplitude-Mode Spectroscopy of Charge Excitations in PTB7 π-Conjugated Donor-Acceptor Copolymer for Photovoltaic Applications
AffiliationUniv Arizona, Coll Opt Sci
MetadataShow full item record
PublisherAMER PHYSICAL SOC
CitationAmplitude-Mode Spectroscopy of Charge Excitations in PTB7 π-Conjugated Donor-Acceptor Copolymer for Photovoltaic Applications 2017, 7 (6) Physical Review Applied
JournalPhysical Review Applied
Rights© 2017 American Physical Society
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at firstname.lastname@example.org.
AbstractWe measure the spectra of resonant Raman scattering and doping-induced absorption of pristine films of the pi-conjugated donor-acceptor (D-A) copolymer, namely, thieno[3,4 b] thiophene-alt-benzodithiophene (PTB7), as well as photoinduced absorption spectrum in a blend of PTB7 with fullerene phenyl-C61-butyric acid methyl ester molecules used for organic photovoltaic (OPV) applications. We find that the D-A copolymer contains six strongly coupled vibrational modes having relatively strong Raman-scattering intensity, which are renormalized upon adding charge polarons onto the copolymer chains either by doping or photogeneration. Since the lower-energy charge-polaron absorption band overlaps with the renormalized vibrational modes, they appear as antiresonance lines superposed onto the induced polaron absorption band in the photoinduced absorption spectrum but less so in the doping-induced absorption spectrum. We show that the Raman-scattering, doping-, and photoinduced absorption spectra of PTB7 are well explained by the amplitude mode model, where a single vibrational propagator describes the renormalized modes and their related intensities in detail. From the relative strengths of the induced infrared activity of the polaron-related vibrations and electronic transitions, we obtain the polaron effective kinetic mass in PTB7 using the amplitude mode model to be approximately 3.8m*, where m* is the electron effective mass. The enhanced polaronic mass in PTB7 may limit the charge mobility, which, in turn, reduces the OPV solar-cell efficiency based on the PTB7-fullerene blend.
VersionFinal published version
SponsorsAir Force Office of Scientific Research (AFOSR) [FA9550-16-1-0207]; National Science Foundation-Materials Research, Science, and Engineering Center (NSF-MRSEC) [DMR 1121252]; Space Exploration and Optical Solutions Technology Research Initiative Fund at the University of Arizona