2014 年 35 巻 11 号 p. 621-626
Time-resolved electron paramagnetic resonance (TREPR) spectroscopy has been utilized at T = 77 K to characterize geometries and electronic couplings (VCR) of transient charge-separated (CS) states in photoactive layers in organic thin film solar cells fabricated by spin-coating of mixed solutions of polyalkylthiophenes (RR-P3AT) and [6, 6]-C61-butyric acid methyl ester (PCBM). Electron-hole distance of the interfacial transient CS states has been revealed to be modulated by alkyl side-chain number in P3AT. This result is explained by a coupling of a hole dissociation to polymer librations by the side-chains. From an exponential decay of VCR with respect to the CS distance, an attenuation factor (βe) of the decay has been determined to be βe＝0.2 Å−1. Such a long-range tunneling feature is explained by generations of shallowly trapped, delocalized electron-hole pairs by the dissociations of the hole toward π-stacking directions at the organic photovoltaic interface.