ABSTRACT
Phosphors are solid luminescent materials doped with activator ions. Different types of phosphor host have been available for the past few decades: typically oxides, nitrides, oxynitrides, sulfides, halides, silicates, aluminum, and silicon. Upconversion is a process in which the sequential absorption of two or more photons leads to the emission of light at a shorter wavelength than the incident wavelength. One of the major energy-loss mechanisms that affect the energy-conversion efficiency of Si-solar cells is the thermalization of the charge carriers, that are attributed via the absorption of high-energy photons. Solar cells can be broadly categorized into three generations. The first generation includes solar cells that are relatively higher in cost to fabricate and have low conversion efficiency. The second generation involves types of solar cells that have lower efficiency but are much cheaper to fabricate, and the solar cell cost per watt is lower than in first-generation cells. The third generation of photovoltaic solar cells are very efficient.
