The development of new materials for optoelectronic applications requires two intertwined research directions: finding materials with the required optoelectronic properties, and striving to find suitable methods to prepare thin films of materials for building experimental devices and final commercial systems. In order to balance those electronic characteristics with the morphology of the materials studied, a compromise must be made in determining these two directions. Now, researchers at Osaka University have developed a two-step process that can produce materials with good morphological properties in addition to excellent photoresistor properties.
Osaka chemists Ryosuke Nishikubo and Saeki Akinori Saeki turned to bismuth sulfide (Bi2S3) in their research. This material is one of the metal chalcogenide materials with good optical and electronic properties. Unfortunately, the performance of these materials' photoreaction devices depends to a large extent on how the necessary films are handled, making them significantly less useful in applications. Early development of bismuth sulfide was hampered by the low crystallinity of the film. In addition, even those thin films with high crystallinity often have a negative impact on their properties. Therefore, films with low surface roughness and large particle size are highly needed, which is the focus of the Osaka team.
Saeki explained: "We searched over 200 materials with a unique ultra-high-speed screening method that can evaluate the performance of materials, even with powder samples. We found that they are comparable In comparison, bismuth sulfide is inexpensive and less toxic, and can be processed without compromising its excellent photoelectric properties. "
The team spin-coated with the solution and then crystallized to form a two-dimensional layered film of the material in two processing steps. They examined the light-response performance of the resulting film and found that it was at least 6 times, and even up to 100 times, the performance observed with films treated by other methods.
Nishikubo added: "We believe that solution-processed bismuth-based semiconductors are a viable alternative to commercial inorganic solar cells and are expected to be widely used in the future." The team also demonstrated that other metal sulfide semiconductors can be prepared as response films using the same method .