While t-Se is sometimes referred to as a 'direct' band gap absorber in the experimental literature -due to a small energy difference and weak signal of indirect absorption in thin films, it is in fact a 'pseudo-direct' gap material with (DE g, direct/indirect ' 0.1 eV). Taking the experimentally-reported fundamental band gap of ⇠ 1.85 eV and assuming a thin-film architecture with weak indirect absorption contributions, t-Se has a theoretical maximum efficiency of h ' 22.6% and V oc, max = 1.56 V for a single-junction solar cell, under the detailed-balance limit. We see that current record efficiencies of single-junction Se photovoltaics (7.2 % and 18.0 % for solar and indoor PV) stand at around a third of the theoretical limits (22.6 % and ⇠50 % respectively). As with most emerging solar absorbers, the primary origin of efficiency loss relative to the radiative limit is a relatively low open-circuit voltage V oc . The record V oc for selenium solar cells sits at just under 1 V, corresponding to a voltage deficit (DV oc ) of about 0.56 V, or 36 %, compared to the ideal value at the radiative limit. The dominant contribution to this V oc deficit, whether Urbach tailing, limited doping densities, electron-hole recombination or other mechanisms, has been the focus of several studies in recent years, however the exact split of the relative contributions is not yet known. Nevertheless, it is thought that defect-mediated non-radiative electron-hole recombination is a primary contributor to the V oc deficit -being the typical limiting factor for emerging solar cell technologies. A related open question is the origin of the apparent high doping densities in as-grown t-Se samples. In early research on crystalline selenium, it was reported that single crystals had hole densities on the order of 10 14 cm 3 , while polycrystalline samples exhibited a wide range of reported hole concentrations between 10 13 -10 17 cm 3 . Nielsen et al. and others have reported doping densities on the order of 10 15 -