The advancement of photocatalytic systems for solar fuel production requires careful control over the structures and properties of metal oxide semiconductor materials. In this talk, I will present integrated synthesis strategies that combine Physical Vapor Deposition with Rapid Photonic Annealing,^[1] demonstrating how these methods address different material challenges across the semiconductor synthesis spectrum to unlock the potential of solar fuels.

Using Bi₂O₃ as a model binary system (chosen for its relatively accessible processing temperatures and well-characterized polymorphism), we demonstrate kinetic control of crystal polymorphism through Flash Photonic Heating (FPH, heating rates of 10⁶-10⁷ °C/s), achieving reversible α↔β phase transformations. Controlling polymorphism is critical because metastable phases often exhibit superior optoelectronic properties - the β-phase shows substantially enhanced photocurrent density and reduced bandgap compared to the thermodynamically stable α-phase. While pulsed laser deposition enhances film quality by delivering energies orders of magnitude higher than those of chemical methods for precise stoichiometric control, FPH enables polymorph control at accessible temperatures, providing insights into kinetic versus thermodynamic crystal-formation pathways.

At the opposite end of the synthesis-complexity spectrum, high-entropy rare earth oxides (HEREOs) such as (Ce₀.₂Zr₀.₂La₀.₂Pr₀.₂Y₀.₂)O₂ require integrated strategies to fulfill their potential for enhanced catalytic performance and structural stability. These chemically complex, refractory materials need the combined high-energy deposition techniques of physical vapor deposition with the unique thermal processing capabilities of rapid photonic annealing to ensure proper crystallization and controlled nanostructuring. FPH allows the formation of nanoscale grains and increased surface areas that are practically impossible to achieve with conventional thermal processing, unlocking the catalytic potential crucial for next-generation energy conversion systems.

This materials-spanning approach shows how synthesis requirements shift from controlling polymorphs for better optoelectronic properties in binary systems to integrated nanostructuring strategies for improved catalytic performance in high-entropy materials. The presentation will illustrate how understanding these different challenges offers key pathways for developing advanced metal oxide semiconductors for solar fuel applications.