A review on Z/S – scheme heterojunction for photocatalytic applications based on metal halide perovskite materials

As an emerging class of semiconductors, Metal Halide Perovskites (MHPs) form a major paradigm of photocatalysts for its truly unique and superior optoelectronic properties over the traditional class of photocatalysts. Based on the similar phenomenon of a plant's chlorophyll, photocatalysts use solar radiation to split water into oxygen and hydrogen. MHPs, therefore significantly contribute to the photocatalysts family as a novel and rapidly expanding technological advancement. Whereas the Z-scheme heterojunction is a charge transfer mechanism that promotes diversified photocatalytic operations by utilizing its ability to use sunlight, correctly synthesized semiconductor photocatalysts are potential substances for addressing today's major energy and environmental concerns. Expanding the number of active reductive and oxidative sites and possessing high redox capacity are just a handful of advantages of the recently designed photocatalysts which closely mimic the actual photosynthesis mechanism. An efficient direct Z scheme heterojunction, a photocatalytic system combined with MHPs, enables us to create photocatalysts with significantly higher efficiency and activity. By combining a second semiconductor constituent with the appropriate band arrangement offsets, a Z-scheme photocatalytic system can be created, enabling the innate competencies of perovskites to be fully utilized. However, the low photocatalytic efficiency of the traditional Z-scheme photocatalysts inspires us towards more efficient step-scheme (S-scheme) photocatalysts, and alternatively dwell more into developing heterojunctions for incorporating a multitude of essential properties. This review paper focuses on the basic understanding of the different classes of photocatalysts studied in the academic world, which would rather be important to define why MHP may be successful in its endeavor of being a successful class of photocatalysts for different applications like CO2 reduction and H2 evolution. However, given that MHPs are still in infancy to be considered commercially, it would be important to underline the present readiness level of this technology and drawbacks if any and therefore, it would be imperative to lay down a future roadmap on the development of these photocatalysts.