Sustaining Sub-bandgap Photons via Upconversion for Solar Splitting Cells

Conservation of the entire spectrum of the sun is crucial to raising the efficiency of solar splitting cells or any photochemical conversion. With the aid of upconversion nanomaterials, it could potentially be achievable. In general, solar splitting technologies are associated with numerous losses. Remarkably, inadequate utilization of the light spectrum is the primary cause of losses in photophysical processes. This is usually caused by a particular band gap in semiconductor materials, where higher-energy photons dissipate as energy and lower-energy photons, or sub-bandgap photons, are unable to be absorbed. The process of absorbing two or more photons and then emitting one photon with more energy than the sum of the individual energies of the previously absorbed ones is known as upconversion. Introducing an appropriate upconverter can significantly improve the photoconversion process’s efficiency. Efforts have been made in the past few years to enhance the efficiency, broad-range sensitivity, and activity of semiconductors by integrating upconversion systems. This chapter provides a detailed discussion of the upconversion strategies that have been used thus far to increase the efficiency of solar splitting cells. It will undoubtedly assist the researchers in advancing in this area.