Sulfures mixtes de bismuth et d’antimoine Bi_xSb_2–x S₃ utilisés comme photoélectrodes

¹ Laboratoire de Physicochimie des Interfaces, Ecole Centrale de Lyon, B.P. 163, 36, avenue Guy de Collongue, 69131 Ecully Cedex, France.
² Laboratoire de Chimie Minérale, Université Lyon 1, 69622 Villeurbanne, France, France.

Résumé

Le comportement photoélectrochimique des solutions solides de semi-conducteurs de type n Bi_x Sb_2–x S₃ a été étudié sur l’intervalle 0 < x < 2. Les photoélectrodes ont été obtenues par réaction gaz-solide de H₂S sur les alliages métalliques. La bande interdite varie de façon régulière de 1,62 eV (x = 0) à 1,22 eV (x = 2) alors que le potentiel d’apparition du photocourant reste pratiquement inchangé. Pour la composition x = 0,68 correspondant à la bande interdite la mieux adaptée â la conversion solaire les photoélectrodes présentent une stabilité supérieure aux sulfures simples de bismuth et d’antimoine.

Abstract

The photoelectrochemical behaviour of the solid solutions Bi_xSb_2–x S₃ has been investigated over the full range 0 < x < 2.0. Photoelectrodes were made by tarnishing reactions between H₂S and metal alloys of different compositions. The sulphides are n-type. The bandgap varies continuously from 1.62 eV (x = 0) to 1.22 eV (x = 2.0). In the composition region in the neighbourhood of x = 0.68 the photoelectrodes show enhanced stability with respect to both Sb₂S₃ and Bi₂S₃ as regards photocorrosion in aqueous electrolyte. In addition, in this composition range the bandgap is ideally suited to solar energy conversion. The photocurrent onset potential does not change with x which is indirect evidence that the flatband potential does not change. It can be shown that the rate of the hole reducing agent reaction cannot in principle pass through a maximum as x, and hence the position of the valence band changes. We thus attribute the enhanced stability to a kinetic barrier to photocorrosion created by the non-existence of solid solutions of bismuth and antimony oxides and hydroxides in the intermediate range of x.