Urbach edge analysis is a useful way to parametrically characterize a film’s optical absorption edge and to distinguish
intrinsic and extrinsic contributions to the absorbance [44].
Urbach[46] originally observed that a material’s optical absorption for energies below the fundamental optical absorption edge
is exponential in nature and can be characterized by the Urbach
edge energy (E0) and the Urbach width (W), which is related to
the slope of the Urbach edge (using the nm3eV conversion,
l(nm)¼1239.8/E (eV)).