  Organic semiconductors are disordered molecular solids and as a result, their
internal charge dynamics and ultimately, the performance of the optoelectronic
devices they constitute, are governed by energetic disorder. To ascertain how
energetic disorder impacts charge generation, exciton transport, charge
transport, and the performance of organic semiconductor devices, an accurate
approach is first required to measure this critical parameter. In this work, we
show that the static disorder has no relation with the so-called Urbach energy
in organic semiconductors. Instead, it can be obtained from photovoltaic
external quantum efficiency spectra at wavelengths near the absorption onset.
We then present a detailed methodology, alongside a computational framework,
for quantifying the static energetic disorder associated with singlet excitons.
Moreover, the role of optical interference in this analysis is considered to
achieve a high-accuracy quantification. Finally, the excitonic static disorder
was quantified in several technologically-relevant donor-acceptor blends,
including high-efficiency PM6:Y6.
