Photochargeable Semiconductors: in "Dark Photocatalysis" and Beyond

Photochargeable semiconductors enable energy harvesting and storage in a single material. Charges separated upon absorption of photons can accumulate in highly energetic trap states if morphology, size, and chemical composition are appropriately chosen. For example, electrons can survive for several hours if hole scavengers are used to prevent their recombination with photogenerated holes, and their negative charge is balanced by positive counter-ions. The first database of charge-storing semiconductors is recently released, containing information from more than 50 publications within the past 40 years. Now, the database has been updated with more than 90 entries from the latest works on the topic. These materials have been largely utilized in the context of "dark photocatalysis", that is, redox reactions enabled by photocharged semiconductors long after cessation of light irradiation. Nevertheless, a variety of further potential applications have not received enough visibility, including memory storage, steel anti-corrosion, sensors, and micromotors. In this review, the key figures of merit of photocharged semiconductors and the empirical relationships found between them is highlighted. After showing the latest advances in dark photocatalysis, it is discussed how other application fields may benefit from these materials. For each area, promising research directions based on the findings from the database are recommended.