Analysis of enargite thin films synthesized from carbon-containing and novel carbon-free processing methods

Current processing routes to produce thin films of emerging photovoltaic absorber Cu3AsS4 enargite use nanoparticle-based solution precursors that leave impurities in treated films. Spatial mapping of these carbonaceous impurities and analysis of their probable formation pathways reveal effective strategies toward avoiding secondary phase formation in these films. Leveraging these results, new fabrication pathways are introduced for thin enargite films based on evaporated copper precursor films. Unlike nanoparticle-based films, evaporated copper-based enargite films do not contain a carbonaceous residue, a Raman-active secondary phase, or a fine-grain layer. Enargite films produced from the conversion of evaporated copper films to copper sulfide are compared with nanoparticle-based films through current density-voltage analysis. Surprisingly, these films have similar photoconversion efficiencies which indicate the carbonaceous secondary phases are not responsible for current low-efficiency technology. A post-deposition diammonium sulfide solution etch is investigated to remove arsenic-based secondary phases and produces the highest short circuit currents, fill factors, and efficiencies to date for enargite-based photovoltaic technology. By introducing precursor films and processes that result in phase-pure enargite films, this work broadens the scope of synthesis pathways to enable more scalable processing methods that can inform effective strategies for the development of this emerging PV technology.