The Shockley–Queisser Limit Recomputed: Detailed Balance under a 6000 K Blackbody and the AM1.5G Spectrum, a Loss Ledger, and a Two-Junction Extension

Recomputation of the single-junction solar efficiency limit from detailed balance under (a) a geometrically diluted 6000 K blackbody sun and (b) the ASTM G173-03 AM1.5G spectrum, with radiative recombination only. Blackbody limit: 30.96% at 1.306 eV (30.04% at 1.10 eV, reproducing the 1961 value). AM1.5G limit: 33.69% at 1.336 eV. An exact loss ledger at the AM1.5G optimum gives 29.7% below-bandgap photons, 23.3% thermalisation, 9.1% radiative-emission voltage deficit, 4.2% fill factor, 33.7% delivered. The difference between the 1961 and modern values decomposes entirely into bandgap choice (+0.92 points), irradiance normalisation (-0.38 points), and spectrum shape (+3.11 points). A two-junction stack under AM1.5G reaches 45.64% series-connected. All numbers are computed by the archived script from the archived spectrum table.