  Many semiconductors present weak or forbidden transitions at their
fundamental band gaps, inducing a widened region of transparency. This occurs
in high-performing n-type transparent conductors (TCs) such as Sn-doped In2O3
(ITO), however thus far the presence of forbidden transitions has been
neglected in searches for new p-type TCs. To address this, we first compute
high-throughput absorption spectra across ~18,000 semiconductors, showing that
over half exhibit forbidden or weak optical transitions at their band edges.
Next, we demonstrate that compounds with highly localized band edge states are
more likely to present forbidden transitions. Lastly, we search this set for
p-type and n-type TCs with forbidden or weak transitions. Defect calculations
yield unexplored TC candidates such as ambipolar BeSiP2, Zr2SN2 and KSe, p-type
BAs, Au2S, and AuCl, and n-type Ba2InGaO5, GaSbO4, and KSbO3, among others. We
share our data set via the MPContribs platform, and we recommend that future
screenings for optical properties use metrics representative of absorption
features rather than band gap alone.
