Unfused core units 130 and 28 are structurally similar, with unit 130 having the diphenylamine units functionalized with sulfur. Both units have shallow HOMO energy levels, implying they are strongly electron-donating. Unit 130 is found in NFA SCH3, while unit 28 is in CH3-2F, the only difference in these NFAs being this central unit . Adding substituents like sulfur affected the extinction coefficient and miscibility with the donor material. This unit led to a slightly twisted backbone, adopting a 3D conformation that suppressed over-aggregation, allowing for an efficient charge transport network. Since this project has been completed, a new record-breaking unfused NFA has been published with unit 28 as its central backbone, giving a PCE of 15.44% with donor D18 . The other top unfused units (ESI Fig. ) commonly appear in current NFAs.