Recent Advances in Luminescent Downconversion: New Materials, Techniques, and Applications in Solar Cells

Numerous investigations have been done in pursuing phosphors with quantum yield (QY) greater than unity in terms of downconversion (DC) strategies, as well as applications in display, lighting, and particularly in novel solar cells with efficiency exceeding the Shockley-Queisser limit (approximate to 30%). It is of significant interest that: i) DC of one high-energy photon to two or more low-energy photons is widely found in lanthanide and/or transition-metal ions activated materials; ii) broadening of absorption spanning ultraviolet/blue range is achieved by introducing sensitizers with spin-allowed transitions and especially by combining the advancing perovskite quantum dots, nanostructures, and organic dye molecules; iii) internal QY >> 1 and even measured QY > 1 are claimed in many near-infrared (NIR) DC systems; iv) applications of downconverting layer atop commercial solar cells are performed to increase the photon conversion efficiency. In this review, the development of DC in theories, concepts, and experiments is first summarized, then the breakthrough in visible-DC is briefly highlighted, NIR-DC with latest progresses in models, materials, techniques as well as the corresponding optimizations and practices as effective downconverting layers is elaborated, and finally concluding remarks and perspectives in advancing NIR-DC and applications in novel solar cells are given.