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Cu2ZnSn(S,Se)4thin layers processed fromsolution-deposited earth-abundant precursors emerge as absorber materialsfor low-cost thin film solar cells. A frequently observed drawbackof the chemical solution processingpoor crystallinity of thechalcogenide absorbercan be overcome by employing a sodium-containingreactive agent. We demonstrate a massive improvement in grain growthin the presence of sodium. It enhances the surface chemisorption ofselenium molecules and can promote the formation of liquid Na2Sexphases during reactive annealingof the precursor. The sodium is also incorporated into the semiconductorabsorber and significantly modifies its electronic properties. Byadjusting the sodium precursor quantity, it is possible to tune dopinglevels and gradients to maximize the collection of photogeneratedcarriers in thin film Cu2ZnSn(S,Se)4solar cells.The presented approach can be extended to other solution-processedmetal chalcogenides to enhance their structural and electronic properties,which are critical for applications such as thin film solar cellsand transistors. [ABSTRACT FROM AUTHOR]

Solution processing of inorganic thin films has become an important thrust in material research community because it offers low-cost and high-throughput deposition of various functional coatings and devices. Especially inorganic thin film solar cells - macroelectronic devices that rely on consecutive deposition of layers on large-area rigid and flexible substrates - could benefit from solution approaches in order to realize their low-cost nature. This article critically reviews existing deposition approaches of functional layers for chalcogenide solar cells with an extension to other thin film technologies. Only true solutions of readily available metal salts in appropriate solvents are considered without the need of pre-fabricated nanoparticles. By combining three promising approaches, an air-stable Cu(In,Ga)Se2 thin film solar cell with efficiency of 13.8% is demonstrated where all constituent layers (except the metal back contact) are processed from solutions. Notably, water is employed as the solvent in all steps, highlighting the potential for safe manufacturing with high utilization rates. [ABSTRACT FROM AUTHOR]