Solution-Processed Earth-Abundant Cu2BaSn(S,Se)4 Solar Absorber Using a Low-Toxicity Solvent

• Published in: Chemistry of materials Vol. 30; no. 17; pp. 6116 - 6123
• Main Authors: Teymur, Betul, Zhou, Yihao, Ngaboyamahina, Edgard, Glass, Jeffrey T, Mitzi, David B
• Format: Journal Article
• Language: English
• Published: American Chemical Society 11.09.2018
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.8b02556

Cu2BaSn­(S,Se)4 (CBTSSe) has recently gained substantial attention as an alternative absorber material for photovoltaic (PV) and photoelectrochemical (PEC) applications due to the abundance of the constituent elements, a large absorption coefficient, tunable band gap ranging from 1.5 to 2 eV, and reduced tendency for antisite disorder relative to Cu2ZnSn­(S,Se)4. In this study, as an alternative to more expensive vacuum-based film-deposition processes, we report a low-toxicity solution-based process for the fabrication of high quality CBTSSe absorber layers with micrometer-scale film thickness and grain size. The facile process involves spin-coating an environmentally benign solution of highly soluble, inexpensive, and commercially available precursors, Ba­(NO3)2, Cu­(CO2CH3)2, and SnI2, followed by sequential sulfurization/selenization annealing. A high-temperature prebaking step under sulfur vapor is needed for each film layer to avoid forming the difficult-to-remove impurity phase, Ba­(SO4), when starting from the soluble Ba­(NO3)2 reagent. The solution-based CBTSSe films have been employed in a Pt/TiO2/CdS/CBTSSe photocathode structure (e.g., for water splitting), exhibiting an ∼10 mA/cm2 current density at 0 VRHE, comparable to that of vacuum-deposited CBTSSe PEC devices. Our approach for the fabrication of CBTSSe absorbers represents a first step in achieving low-cost and large-scale solution-processed solar devices based on this material.