Benzotriazole-based NFAs are known to red-shift absorption and upshift its HOMO compared to benzothiadiazole-based NFAs . Unit 83, found in the NFA AQx-2, has a quinoxaline core, giving rise to a quinoid resonance effect that can decrease reorganization energy and facilitate efficient charge transport . Three of these units contain selenophene, as opposed to thiophene. Compared to sulfur, selenium has a larger atomic radius and more polarizable d-orbitals, leading to better overlap of π-orbitals and a more delocalized electron cloud. Studies on polyselenophene show it has a lower effective mass for holes in the valence band and electrons in the conduction band compared to polythiophene, indicating greater mobility of free charges along the polymer chain . It has also been shown to yield a smaller band gap and red-shifted absorption . Asymmetry appeared in three of the units, with this strategy showing great potential for achieving high fill factors due to the enhanced dipole moment and efficient intermolecular stacking .