The past five years have seen significant cost reductions in photovoltaics and a correspondingly strong increase in uptake, with photovoltaics now positioned to provide one of the lowest-cost options for future electri. Reports of the first efficient silicon solar cells in 19541 stimulated calculations of ultimate photovoltaic efficiency2,3 and its dependence on the semiconductor bandgap (Eg). C. Calculating Shockley–Queisser (SQ) limits follows simply from the above insight. For. One early suggestion — the most practical to date — involved improving efficiency beyond SQ limits, even before these limits were known, by steering different wavelength band. A significant loss in standard cells is the wastage of sub-bandgap photons. One early suggestion for tackling this issue was the use of mid-gap states to capture such photons in a two.