Despite the importance of elucidating photoinduced chargegeneration mechanisms for the development of efficient organic solar cells (OSC), it has been quite difficult to characterize molecular geometries, electronic couplings, and charge mobilities in the initial photoinduced charge-separated (CS) states for the heterogeneous molecular environments in bulk-heterojunction interfaces between electron donor−acceptor domains in the photoactive layers. In this study, we employed a time-resolved electron paramagnetic resonance method to characterize two kinds of electron spin polarizations (ESPs) of the photoinduced CS states as different geometries, exchange couplings, and spin-relaxation times of spincorrelated radical pairs in OSC blend films composed of regioregular poly(3hexylthiophene-2,5-diyl) and [6,6]-phenyl-C 61 -butyric acid methyl ester by applying polarized light excitations (magnetophotoselection) with respect to an external magnetic field direction at a cryogenic temperature. From this, we performed analysis of mapping the ESPs to space directions to obtain image views of the molecular geometries in mobile and trapped CS states. We propose that the heterogeneities in the interfacial charge generations may be correlated with high-and low-frequency phonon modes leading to the mobile and weakly trapped charge pairs, respectively, denoting the great significance of such molecular motions for the efficient photocarriers overcoming the interfacial electrostatic binding potential.

Visible light unlocks the π-electronic conjugation of a dithienylethene-fused p-benzoquinone derivative to cause a light-driven oxidation reaction.

To shed a light on fundamental optoelectronic properties of conjugated polymer films applicable to the organic photovoltaics (OPV), field-effect transistors (FET) and light-emitting diodes (LED), we have characterized interspin separation and exchange coupling of interchain charge-transfer (CT) states in a pristine film of thiophene-thiazolothiazole copolymer by using the time-resolved EPR method. It has been indicated that the CT state is generated at the disordered regions of the polymer films as deep trap sites via the singlet−exciton diffusion in polymer amorphous phase. These characteristics of the trapped charges may limit the device performances in the OPV, FET and LED applications and thus are informative for the device developments.