ELECTROLYTIC SELENIUM PHOTOCELL

Earlier attempts to make electrolytic selenium photocells did not lead to positive results: the photocells obtained had low sensitivity and rapidly lost their photoelectric properties ^1,2. Gippel, Shulman, and Rittner ^3 apparently were the first to give a method for making an electrolytic photocell that is actually suitable for measurement purposes. The selenium photocells obtained by them, at an external voltage of about 2 V, give a short-circuit current on the order of 1000 μA/lm (with a dark current of 0.2–2.0 μA and a surface area of 2 cm²); they possess good linearity over wide ranges of external resistances and intensities and, what is very important, can operate for many months without changing their properties. The spectral sensitivity curve of these photocells is almost the same as that of dry selenium photocells.

The manufacture of an electrolytic selenium photocell is not difficult: two metal electrodes (Pt or stainless steel), coated with electrolytically deposited Se, are immersed in a glass vessel containing an $\mathrm{SeO_2}$ solution. The anodic coating must have a large thickness, since the lifetime of the photocell depends on this. In the article under review the methods of coating the electrodes are described in sufficient detail.

As the authors report, photocells containing $\mathrm{HCl}$, $\mathrm{H_2PO_4}$, $\mathrm{H_2SO_4}$, etc. as electrolytes exhibited photosensitivity, but the selenium layer on the cathode was rapidly destroyed and the photocells failed. Sufficiently sensitive, long-lived, and stable photocells were obtained only with the use of an $\mathrm{SeO_2}$ solution. In this case the cathode is not destroyed, since the following reactions occur:

\[ \mathrm{H_2SeO_3 + 4(-) + 4H^+ = Se + 3H_2O} \quad \text{(at the cathode),} \]

\[ \mathrm{Se + 3H_2O = H_2SeO_3 + 4H^+ + 4(-)} \quad \text{(at the selenium anode).} \]

The authors emphasize that, in order to obtain high sensitivity, the substances used ($\mathrm{Se}$, $\mathrm{SeO_2}$) must have a high degree of purity. Contamination by Te (common) and by other metals in excess of several millionths of a…

… reduced the sensitivity of the photocells obtained many times over, increased the dark current, impaired linearity, etc.

Judging from the materials of the article under review, the shortcomings of the photocells obtained are: the dependence of the dark current on temperature, inertia, which already manifests itself at low frequencies, and considerable variations in the quality of the specimens obtained.

CITED LITERATURE

1. Reinganum, Phys. Zschr. 8, 293. 1907.
2. C. G. Fink and D. K. Alpern, Trans. Am. El. Soc. 62, 369, 1932.
3. A. Hippel, J. H. Schulmann and E. S. Rittner, J. Appl. Phys. 17, 215, 1946.

A. Ilyina