The singlet exciton binding energy, whose distribution is shown in Figure , corresponds to the difference between the GW fundamental gap and the optical gap. This is the energy required to split photogenerated excitons into free charge carriers in organic solar cells. In most organic materials the exciton binding energy is significant compared to inorganic materials because the dielectric screening of charges is not as strong. However, some materials in the PAH101 set have low exciton binding energies (in parentheses), including: anthra ( 0.169 eV). All of these compounds are characterized by very extended and/or elongated π systems, which likely lead to an already low molecular exciton binding energy (not calculated here), further reduced by dielectric screening in the solid form.