“…Currently, these processing issues are primarily addressed for high-efficiency devices by using multistep vacuum-based techniques (e.g., evaporation or sputtering). [9][10][11][12] Several solution-based approaches have also been reported, including (with best power conversion efficiencies achieved) electrochemical deposition (7% for all elements deposited at once, 9% for deposition of metals followed by a separate hightemperature selenization step), [13][14][15] spray pyrolysis/spray chemical vapor deposition (CVD) ( 5%), [16,17] and nanoparticle-precursor deposition (14%). [18][19][20] Limitations of previously reported solution-based CIGS deposition approaches include: (i) incorporation of carbon, oxygen, and other impurities from the precursors or starting solutions; (ii) the need for multistep processing (e.g., a typical nanoparticle process involves making metal oxide nanoparticles, depositing the oxides as films, reducing the films to metals using a hightemperature reduction step, followed by high-temperature selenization); [19,20] (iii) the requirement for a high-temperature selenization/sulfurization step using toxic gases (e.g., H 2 Se) and/or a post-deposition cyanide-bath etch to achieve adequate grain growth and improve phase purity; and (iv) difficulty incorporating dopants such as Ga in a uniform and controllable fashion.…”