2, Mechanical Engineering and Material Science, Duke University, Durham, North Carolina, United States
3, Electrical & Computer Engineering, Duke University, Durham, North Carolina, United States
4, Chemistry, Duke University, Durham, North Carolina, United States
Various chalcogenides (Cu(In, Ga)(S, Se)2, CdTe, Cu2ZnSn(S, Se)4) have been adopted as successful absorber materials for application in thin-film photovoltaic (PV) and photoelectrochemical (PEC) devices. However, despite being commercialized (e.g. Cu(In,Ga)(S,Se)2, CdTe) or showing performance advances (e.g., Cu2ZnSn(S,Se)4), several concerns and material limitations remain regarding scarcity/toxicity (e.g., In and Ga/ Cd) and Cu-Zn anti-site disordering in earth-abundant Cu2ZnSn(S,Se)4(CZTSSe) chalcogenides.Cu2BaSn(S, Se)4(CBTSSe) has recently gained substantial attention as an alternative semiconductor material due to desirable properties for solar energy conversion applications, 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 µm-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)2and SnI2 in DMSO, followed by sequential sulfurization/selenization annealing. A high-temperature pre-baking step under sulfur vapor is needed for each film layer to avoid forming the impurity phase, Ba(SO4) when starting from the soluble Ba(NO3) reagent. Our reproducible approach forms a dense, 1-µm-thick, single phase CBTSSe absorber layer with large grains (0.9-4.5 µm) and a tunable band gap (e.g., 1.68 eV under the typical processing conditions employed). Additionally, we demonstrate the first prototype solution-deposited CBTSSe PEC device, exhibiting a photocurrent of ~10mA/cm2at 0 VRHE((increasing to ∼12 mA/cm2during the stability test), comparable with analogous devices based on vacuum-processed CBTSSe films, as well as stable hydrogen evolution for more than 10 hours. These results demonstrate the prospects for low-cost solution-processing of high-quality CBTSSe film and absorbers for thin film PV and PEC cells.