Fig. 1. Chemical structures, material characterizations, and blend morphologies.

a Molecular structures of small-molecule acceptor BTTT-2Cl, polymer donor PM6, and acceptor additive PZ1. b Normalized UV–vis absorption spectra of the neat films and the PM6:BTTT-2Cl blends without and with dynamics wt% PZ1. c Energy level diagram of PM6, BTTT-2Cl, and PZ1. d Top: Tapping-mode AFM surface scans (size: 5 × 5 μm²) of the PM6:BTTT-2Cl blends without (a root mean square (RMS) roughness of 0.813 nm) and with 1 wt% PZ1 (an RMS roughness of 0.628 nm), the 3.4-nm scale bar applies to AFM images; bottom: 2D-GIWAXS patterns of the corresponding thin films acquired at the critical incident angle of 0.13°. The intensities are shown on a logarithmic scale, as indicated by the color bar.