We investigated carrier formation dynamics in a small-molecular bulk heterojunction solar cell, 2,5-di-(2-ethylhexyl)-3,6-bis-(5″-n-hexy-[2,2′,5′,2″]terthiophen-5-yl)-pyrrolo[3,4-c]pyrrolo-1,4-dione/[6,6]-phenyl C71-butyric acid methyl ester, with low bandgap (Egap≈1.5 eV). The photoinduced absorption (PIA) spectra of the blend film were decomposed into three PIAs, i.e., those due to donor exciton (D*), acceptor exciton (A*), and mobile carrier (D+). The analysis revealed carrier conversion from D* with a conversion time of ∼1.3 ps.

Layered oxide NaxMO2 (M: transition metal) is a promising cathode material for sodium-ion secondary battery. Crystal structure of O3- and P2-type NaxMO2 with various M against temperature (T) was systematically investigated by synchrotron x-ray diffraction mainly focusing on the T-dependences of a- and c-axis lattice constants (a and c) and z coordinate (z) of oxygen. Using a hard-sphere model with minimum Madelung energy, we confirmed that c/a and z values in O3-type NaxMO2 were reproduced. We further evaluated the thermal expansion coefficients (αa and αc) along a- and c-axis at 300 K. The anisotropy of the thermal expansion was quantitatively reproduced without adjustable parameters for O3-type NaxMO2. Deviations of z from the model for P2-type NaxMO2 are ascribed to Na vacancies characteristic to the structure.