Molecular engineering of perylene-diimide-based polymer acceptors containing heteroacene units for all-polymer solar cells

Polymer acceptors based on perylene diimide (PDI) with three symmetrical S-heteroacene backbone units of different sizes were synthesized for use in all-polymer solar cells (all-PSCs). The effects of varying the size of the heteroacene unit on the backbone of the PDI polymer are evident in the absorption spectra and their energy level offsets, which are correlated with their morphological and photovoltaic properties. These newly synthesized polymers were employed as acceptors with the polymer poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-[1,2,5]thiadiazole)] (PPDT2FBT) as the donor in all-PSCs that were found to exhibit modest power conversion efficiencies. The variations in photovoltaic properties of all-PSCs are investigated by characterizing the charge generation, carrier mobilities and recombination. The morphological disorder at the polymer/PPDT2FBT interface and average composition variations are revealed by using grazing incidence wide angle X-ray scattering (GIWAXS) and resonance soft X-ray scattering (R-SoXS) characterizations.