Broad-Spectrum Solar Cell

Due to the energy crisis, utilization of renewable energy sources has been intensively investigated in recent years. Among a variety of renewable energy sources, solar energy is a sustainable alternative option that can be utilized in various ways and can be used for many applications. Converting directly the sunlight to electricity through solar cells is the most common and effective way to use solar energy. The spectral response and overall photo-to-electric energy conversion efficiency of solar cells are closely correlated to the micro band-gap structure and macro assembly process of photovoltaic materials. A solar cell can effectively utilize photons with energy hv close to the semiconductor band gap E-g. Photons with energy smaller than the band gap are not absorbed. On the other hand, photons with energy larger than the band gap are absorbed, but the excess energy hv - E-g is not used effectively due to thermalization. Therefore, a normal single junction or single layer solar cell can only use part of the solar radiation no matter what kind of photovoltaic materials are used. Broad-spectrum solar cell aims to use most of the solar energy effectively via several structures or methods; Tandem solar cells, intermediate-band solar cells, quantum dot solar cells, thermo-photovoltaic solar cells, up-and down-conversion, and molecule based flexible solar cells. During the past few years, many new concepts and results have been emerged in industrial manufactures and laboratory fundamental researches. A survey of recent work is thus necessary to get better insight into this field. This paper summarizes briefly the method and recent progress of broad-spectrum solar cells in viewpoint of chemistry.