Beyond 3rd generation solar cells and the full spectrum project. Recent advances and new emerging solar cells

Solar cells have over 50-years of development history; many different devices and technologies are studied over this time span, and interestingly it is still a hot research topic. Although the physical mechanisms involved in photovoltaic processes are rather fundamental, the characterization and classification of the research pathways seem complicated and can even lead to misleading argumentation. Various photovoltaic devices are classified as first, second- and third- generation based on the developments for the last 25 years to highlight the development history of diverse photovoltaic technologies. This classification may not be appropriate if the recent developments are considered. Wafer based solar cells are regarded as the first-generation and the thin-film solar cells as the second-generation. In the third-generation solar cells, there are many different applications that might be confusing if a firm classification would not be outlined. In the present article, we comprehensively classified the recent developments on the subject and presented an overall perspective. A brief review of the physics and physical mechanisms are given, and based on these mechanisms, a clear classification is outlined. Then, recent experimental and theoretical researches are presented together with a summary of the related review articles recently appeared in the literature.