Fig. 3: Solar energy conversion in PEC separations systems using a single junction without the use of solar concentrators.

Theoretical current density (a) and corresponding efficiency (b) that can be obtained from the semiconductor in a PEC separations system (Eqs. (10)–(11)), as a function of bandgap, and shown for multiple values of the redox potential of the interface (Fig. 1d). c, d The redox potential which should be used for maximum solar energy conversion (left, (c)), the corresponding current density (right, (c)), and the corresponding conversion efficiency η_S (d), all as functions of the semiconductor bandgap E_g. Detailed balance limits are those calculated using the Shockley-Queisser approach^17,27. The entropy-limited efficiency is obtained by correcting the detailed balance limit for entropic overpotential losses required by the second law of thermodynamics as derived in prior work^38,39,40 and described in Supplementary Note 7. Subsequent corrections assuming practical limits on material properties for high-efficiency and earth-abundant materials (Supplementary Note 8) lead to a further reduction in maximum solar efficiency as in prior work¹⁷. The maximum solar efficiency values after each correction are shown in d. Note that the lack of smoothness in computed curves is an artifact of noise in the solar spectrum.