Structure, Dynamics, and Power Conversion Efficiency Correlations in a New Low Bandgap Polymer: PCBM Solar Cell

Molecular packing structures and photoinduced charge separation dynamics have been investigated in a recently developed bulk heterojunction (BHJ) organic photovoltaic (OPV) material based on poly(thienothiophene-benzodithiophene) (PTB1) with a power conversion efficiency (PCE) of >5% in solar cell devices. Grazing incidence X-ray scattering (GIXS) measurements of the PTB1:PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) films revealed π-stacked polymer backbone planes oriented parallel to the substrate surface, in contrast to the π-stacked polymer backbone planes oriented perpendicular to the substrate surface in regioregular P3HT [poly(3-hexylthiophene)]:PCBM films. A ∼1.7 times higher charge mobility in the PTB1:PCBM film relative to that in P3HT:PCBM films is attributed to this difference in stacking orientation. The photoinduced charge separation (CS) rate in the pristine PTB1:PCBM film is more than twice as fast as that in the annealed P3HT:PCBM film. The combination of a small optical gap, fast CS ...