Dr. Sam Hsu’s paper titled “Bandgap Funneling in Bismuth-Based Hybrid Perovskite photocatalyst with efficient Visible-Light-Driven Hydrogen Evolution” has been published (IF: 15.367; DOI: 10.1002/smtd.202200326) and featured as the back cover in Small Methods.

The photocatalytic system using hydrohalic acid (HX) for hydrogen production is a promising strategy for generating clean and renewable fuels as well as value-added chemicals (such as X₂/X ₃^?). A visible-light active and strong-acid resistive photocatalyst is rarely found. Notably, hybrid perovskites have been recognized as a potential photocatalyst for photovoltaic HX splitting. Herein, Dr. Hsu has developed a novel environmentally friendly mixed halide perovskite MA₃Bi₂Cl_9–xI_x with a bandgap funnel structure. Because of the gradient neutral formation energy within iodine-doped MA₃Bi₂Cl₉, the concentration of the iodide element decreases from the surface to the interior across the MA₃Bi₂Cl_9–xI_x perovskite. The aligned energy levels of iodide/chloride-mixed MA₃Bi₂Cl_9–xI_x result in the formation of a graded bandgap funnel structure. This unique structure promotes the photoinduced charge transfer from the interior to the surface, therefore leading to a efficient photocatalytic redox reaction. As a consequence, the anion-exchange technique with the production of the bandgap funnel structure opens up an avenue to design next-generation solar-to-fuel semiconductors for practical applications in the emerging field of energy-generation technology.

Figure. (Left) Synthetic process of all participated samples by adding the varying amount of hydroiodic acid. (right) The energy band diagram of the MA₃Bi₂Cl₉, MA₃Bi₂Cl_9–xI_x and MA₃Bi₂I₉.