Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Third generation photovoltaic cell, also called advanced thin-film photovoltaic cell, is a range of novel alternatives to "first generation" (silicon p-n junction or wafer solar cells) and "second generation" (low-cost, but low-efficiency thin-film) cells. It is an even more advanced version of the thin-film cell. Several new solar cell or photovoltaic technologies, have been proposed or discovered in recent years, due to extensive research and development with a focus on finding more efficient alternatives to traditional silicon solar cells. Research and development in this area generally aims to provide higher efficiency and lower cost per watt of electricity generated. The main criterion Martin Green gives is that the technology aims for extremely high efficiency, "double or triple the 15-20% range currently targeted." The third generation is especially concerned with exceeding the theoretical Shockley-Queisser limit of around 31% for single-junction solar photovoltaic efficiency.