Quantitative relations between interaction parameter, miscibility and function in organic solar cells

L Ye and HW Hu and M Ghasemi and TH Wang and BA Collins and JH Kim and K Jiang and JH Carpenter and H Li and ZK Li and T McAfee and JB Zhao and XK Chen and JLY Lai and TX Ma and JL Bredas and H Yan and H Ade, NATURE MATERIALS, 17, 253-260 (2018).

DOI: 10.1038/s41563-017-0005-1

Although it is known that molecular interactions govern morphology formation and purity of mixed domains of conjugated polymer donors and small-molecule acceptors, and thus largely control the achievable performance of organic solar cells, quantifying interaction-function relations has remained elusive. Here, we first determine the temperature-dependent effective amorphous-amorphous interaction parameter, chi(aa)(T), by mapping out the phase diagram of a model amorphous polymer: fullerene material system. We then establish a quantitative 'constant-kink-saturation' relation between chi(aa) and the fill factor in organic solar cells that is verified in detail in a model system and delineated across numerous high-and low-performing materials systems, including fullerene and non-fullerene acceptors. Our experimental and computational data reveal that a high fill factor is obtained only when chi(aa) is large enough to lead to strong phase separation. Our work outlines a basis for using various miscibility tests and future simulation methods that will significantly reduce or eliminate trial-and-error approaches to material synthesis and device fabrication of functional semiconducting blends and organic blends in general.

Return to Publications page