The charge mobility of organic semiconductors are accurately predicted using first principles simulations validated by inelastic neutron scattering experiments.

Charge transfer doping efficiencies of π-stacked poly(3-hexylthiophene) (P3HT) aggregate nanofibers are studied using spectroscopic and electron microscopy probes. Solution dispersions of self-assembled P3HT nanofibers are doped in the ground electronic state by adding varying amounts (w/w%) of the strong charge transfer dopant, 2,3,5,6-tetrafluoro-7,7,8,8tetracyanoquinodimethane (F 4 -TCNQ). Careful control of self-assembly conditions allows us to select either the H-and J-aggregate limiting forms, which differ primarily in the degree of purity (i.e., molecular weight fractionation) and nanomorphology. Electron paramagnetic resonance (EPR), electronic absorption, and Raman spectroscopy of F 4 -TCNQ -:P3HT + species are then used

Photoluminescence (PL) of single poly(3-hexylthiophene) (P3HT) J-aggregate nanofibers (NFs) exhibits strong quenching under intensity-modulated pulsed excitation. Initial PL intensities (I(0)) decay to steady-state levels (ISS) typically within ∼ 1-10 μs, and large quenching depths (I(0)/I(SS) >2) are observed for ∼ 70% of these NFs. Similar studies of polymorphic, H-aggregate type P3HT NFs show much smaller PL quenching depths (I(0)/I(SS) ≤ 1.2). P3HT chains in J-type NF π-stacks possess high intrachain order, which has been shown previously to promote the formation of long-lived, delocalized polarons. We propose that these species recombine nongeminately to triplets on time scales of >1 ns. The identity of triplets as the dominant PL quenchers was confirmed by subjecting NFs to oxygen, resulting in an instantaneous loss of triplet PL quenching (I(0)/I(SS) ∼ 1). The lower intrachain order in H-type NFs, similar to P3HT thin-film aggregates, localizes excitons and polarons, leading to efficient geminate recombination that suppresses triplet formation at longer time scales. Our results demonstrate the promise of self-assembly strategies to control intrachain ordering within multichromophoric polymeric aggregate assemblies to tune exciton coupling and interconversion processes between different spin states.

Resonance Raman-photocurrent imaging (RRPI) is introduced to spatially map the morphology-dependent polymer aggregation state to local photocurrent generation efficiency in poly-(3-hexylthiophene) (P3HT) and [6,6]phenyl-C 61 -butyric acid methyl ester (PCBM) blend thin film photovoltaic devices. The CdC symmetric stretching mode of P3HT is decomposed into contributions from aggregated (I CdC agg , ∼1450 cm -1 ) and unaggregated (I CdC un , ∼1470 cm -1 ) chains, and the ratios of their integrated intensities (I CdC agg /I CdC un , R) is used as a reporter for the local P3HTaggregation state. Maps of R values and photocurrents are generated for both as-cast and annealed P3HT/PCBM devices that permit direct spatial correlations between the P3HT aggregation state and local photocurrent generation efficiency. Regions of increased P3HTaggregation are observed at both P3HT/ PCBM interfaces and in P3HT-rich areas that result in decreased photocurrent generation. Voltage-dependent RRPI studies are also performed at several applied bias levels that reveal distinct changes in photocurrents due to morphologydependent charge mobility characteristics.