Pulsed chemical vapor deposition of Cu2S into a porous TiO2 matrix

Abstract

Experimental and theoretical investigation of the electronic structure of Cu2O and CuO thin films on Cu(110) using x-ray photoelectron and absorption spectroscopy Chalcocite (Cu 2 S) has been deposited via pulsed chemical vapor deposition (PCVD) into a porous TiO 2 matrix using hydrogen sulfide and a metal-organic precursor. The precursor used is similar to the more common Cu(hfac)(tmvs) precursor, but it is fluorine free and exhibits increased thermal stability. The simultaneous exposure of the substrate to the copper precursor and hydrogen sulfide resulted in nonuniform Cu 2 S films with a temperature independent deposition rate implying gas phase reaction kinetics. The exposure of mesoporous TiO 2 and planar ZnO to alternating cycles of the copper precursor and hydrogen sulfide resulted in a PCVD film that penetrated fully into the porous TiO 2 layer with a constant deposition rate of 0.08 nm/cycle over a temperature range of 150-400 C. The chalcocite (Cu 2 S) stoichiometry was confirmed with extended x-ray absorption fine structure measurements (EXAFS) and x-ray photoelectron spectroscopy. Calculations of the EXAFS spectrum for different Cu x S phases show that EXAFS is sensitive to the different phase stoichiometries. Optical absorption measurements of CVD thin films using photothermal deflection spectroscopy show the presence of a metallic copper-poor phase for gas phase nucleated films less than 100 nm thick and a copper-rich semiconducting phase for thicknesses greater than 100 nm with a direct band gap of 1.8 eV and an indirect bandgap of 1.2 eV.

Structural, optical, and electronic stability of copper sulfide thin films grown by atomic layer deposition

“…21 However, CVD routes identied to date show evidence for sub-stoichiometric phase impurities and a degenerate doping ($10 20 cm À3 ) that is unsuitable for applications in solar energy conversion. 14,[22][23][24] Several wet chemical syntheses for copper chalcogenide nanocrystals have now also been reported, many of which are far from stoichiometry, but the most recent of which show improved control over phase and Cu : S ratio in asprepared samples. 2,25 Nonetheless, the high surface to volume ratio of these nanomaterials present a further challenge to stabilizing the electronic and optical properties for use in devices.…”

Solution-Processed Cu2S Photocathodes for Photoelectrochemical Water Splitting

“…Methods to prepare Cu 2 S films include spray pyrolysis, 17 atomic layer deposition (ALD), 8,9,18 pulsed chemical vapor deposition (PCVD), 19,20 electrodeposition, 21 ion exchange reaction, 11,22,23 and solid-state reaction. 24,25 However, most of these films are not photoactive because of the poor control of stoichiometry.…”

Thiol‐Amine‐Based Solution Processing of Cu2S Thin Films for Photoelectrochemical Water Splitting

“…Many methods have been used to prepare Cu 2 S thin films, including cation exchange reaction, [9] electrodeposition, [17] spray pyrolysis deposition, [18] pulsed chemical vapor deposition, [19] physical vapor deposition, [20] and atomic layer deposition (ALD). [ 21 , 22 ] However, there are only few solar energy conversion devices based on the aforementioned methods, presumably due to the lack of phase purity.…”