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CuIn5S8 was prepared by gradient freeze techniques. Doping was done, and annealing was carried out under various sulfur atmosphere vapor pressures and vacuum. HgIn2S4 was prepared by chemical vapor phase transport and was annealed under various sulfur vapor pressures. Both materials showed increased photocurrent density with photoetching at short circuit, which was particularly dramatic for HgIn2S4 . Purely n‐type response was seen for HgIn2S4 samples as well as for CuIn5S8 , except where phosphorus plus sulfur dopants were used (both n‐ and p‐type responses). Quantum efficiencies of carrier collection were 10–15% at short circuit for CuIn5S8 (maximum of 77%) and ∼22% for HgIn2S4 (maximum of 83%) in a polysulfide couple. Considerable increase in the short‐circuit current density and open‐circuit photovoltage could be obtained for CuIn5S8 in a Ce4+/3+ couple, but this was offset by substantial photocorrosion. Power efficiencies up to ∼0.4% and ∼0.2% were obtained for CuIn5S8 and HgIn2S4 , respectively. Stability in a polysulfide couple was up to ∼97% for CuIn5S8 and >99% for HgIn2S4 .

The photoelectrtichdmical properties of the two p-type title semiconductors were examined in several redox solutions for the first time. For p-HgIn2Te4, the quantum efficiency for carrier collection (0C) is 94% at short circuit, and the monochromatic and polychromatic power efficiencies calculated from three electrode cell experiments are 9.5% and 3%, respectively, in iron(III) triethanolamine solution with comparably high values in [Cr(III)EDTA]'. The flat-band potential (Kft) is at -0.70 V (vs. SCE) in the former two couples, and indirect and direct gap transitions exist at 0.88 and 1.04 eV, respectively. Stability studies indicate essentially 100% stability to photocorrosion in Fe(III)TEA. For p-CdIn2Te4, 0C is also high at short circuit (91%) and the monochromatic power efficiency is even higher (11%) than for p-Hg!n2Te4 while the polychromatic value is somewhat lower (2%), both calculated from three electrode cell experiments. The Kn, is at approximately -0.5 V (vs. SCE), and both an indirect (1.16 eV) and a direct transition exist (1.24 eV). Data for both semiconductors in a polysulfide solution indicate considerably poorer PEC characteristics than for the other redox solutions.

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The photoelectrochemical behavior of p‐HgIn2Te4 (I) and p‐CdIn2Te4 ((II), Ag‐doped) have been explored for the first time using two very different pH redox couples, the CrEDTA complex (pH 4.5) and Fe(III) triethanolamine (pH 13).