High-Throughput Screening of High-Entropy Fluorite-Type Oxides as Potential Candidates for Photovoltaic Applications

High-throughput (HT) synthesis and HT characterization techniques are becoming increasingly important due to the ever-increasing complexity of materials and applications of advanced functional compounds. This work reports on the high-throughput compilation of material libraries of high-entropy oxides with fluorite crystal structure and tunable band gaps to be used as, e.g., semiconductors for photovoltaic applications. The material libraries cover the high-entropy range of rare-earth oxides with 5, 6, and 7 different cations (Ce, La, Sm, Pr, Tb, Y, and Zr) in near equimolar concentrations, but also the medium entropy range with 4 cations. The atmosphere used during or after synthesis is found to have a large effect on the band gap of these materials. Multivalent rare-earth cations such as Ce/Pr/Tb enable reversible tuning of the band gap between 2.0 and 3.5 eV upon calcination under various oxidizing and reducing atmospheres. The high-entropy fluorite oxides with smaller band gaps exhibit high electron mobility and transport energy levels compatible with common solar cell architectures.