Amorphous and organic semiconductors have strong topological irregularities with respect to specific ideal structures, which depend on the particular class of such semiconductors. Most of these defects are rather gradual displacements from an ideal surrounding. The disorder leads to defects levels with a broad energy distribution which extends as band tails into the bandgap. Instead of a sharp band edge known from crystalline solids a mobility edge exists separating between extended states in the bands and localized states in the band tails.
Böer, K. W., Pohl, U., Böer, K. W., & Pohl, U. W. (2016). Defects in Amporphous and Organic Semiconductors. In Semiconductor Physics (pp. 1–32). Springer International Publishing. https://doi.org/10.1007/978-3-319-06540-3_20-1