Time-Resolved EPR Study of Electron-Hole Dissociations Influenced by Alkyl Side Chains at the Photovoltaic Polyalkylthiophene:PCBM Interface.
Nanosecond time-resolved electron paramagnetic resonance (TREPR) spectroscopy has been utilized at T = 77 K to characterize alkyl side-chain effects on geometries and on the electronic couplings (VCR) of transient charge-separated (CS) states in the photoactive layers fabricated by the spin-coating of mixed solutions of regioregular polyalkylthiophenes (RR-P3AT) and [6,6]-C61-butyric acid methyl ester (PCBM). By increasing the alkyl side-chain number from 6 to 12 in P3AT, a highly distant and long-lived CS state has been obtained. This result is explained by a coupling of the hole dissociation to the polymer librations by the side-chains. From an exponential decay of VCR with respect to the CS distance, the attenuation factor (βe) has been determined to be βe = 0.2 Å(-1). Such a long-range tunneling feature is explained by the generations of the shallowly trapped, delocalized electron-hole pairs by the dissociation of the hole toward π-stacking directions at the organic photovoltaic interface.
†Department of Chemistry, Graduate School of Science, Shizuoka University, 836 Ohya Suruga-ku, Shizoka 422-8529, Japan.
Taku
T
Miura
†Department of Chemistry, Graduate School of Science, Shizuoka University, 836 Ohya Suruga-ku, Shizoka 422-8529, Japan.
Motoko
M
Aikawa
‡Department of Chemistry, Graduate School of Science, Kobe University, 1-1 Rokkoudai-cho, Nada-ku, Kobe 657-8501, Japan.|§PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi-shi, Saitama 332-0012, Japan.
Yasuhiro
Y
Kobori
charge separation; electron tunneling; entropy; organic thin film solar cell; spin correlated radical pair; trap depth