Electrochemically Deposited Sb and in Doped Tin Sulfide (SnS) Photoelectrodes

Semiconducting tin sulfide (SnS) was deposited electrochemically from electrolytes containing Sn and S precursors and conditions optimized to maximize its performance as a photoelectrode. Films composed of primarily,orthorhombic SnS were electrodeposited on titanium substrates from electrolyte containing 20 mM SnSO4 and 100 mM Na2S2O3 at pH 2.5. For deposition a cathodic pulse of 1.25 V vs Ag/AgCl was applied for 2.75 s followed by a 0.25 s pulse of +0.25 V vs Ag/AgCl repeated for 30-45 min. The films were annealed in argon at 300 C for 3 h. The addition of SbCl3 (<5%) to the electrolyte gave rise to doping of the SnS film with Sb which resulted in an increase in the photocurrent as well as a switch from p- to n-type semiconducting behavior in an acidified Na2S2O3 electrolyte. Incorporation of p-type In into the films from addition of In(NO3)(3) had a smaller effect on the measured photocurrent, and at higher precursor concentration (>5%) the dopants resulted in the formation of secondary phases of Sb and In oxides with reduction in the measured photocurrent. This doped SriS material could potentially be used in systems for the photoelectrochemical production of hydrogen and oxidation of organic wastewater. Density functional theory calculations supported the experimentally observed conductivity increase for photoelectrons as an Sb dopant induced curvature of the valence band. These calculations also provided an explanation to the previous experimental work where Sb doping was used to decrease the resistivity of SnS films. The combination of an automated electrodeposition of an earth abundant metal sulfide with the theoretical calculations to guide the synthesis is an exemplar of how to improve the efficiency of SnS-based solar energy conversion materials.