Abstract
Our sun is the only sustainable energy source large enough to supply carbon-neutral energy to meet humanity's entire energy demand. However there is a large gap between Europe's solar energy use (less than 1% of the total) and the enormous, untapped potential of the sun. There could be several reasons listed why it is so-social, political, technological--but the fundamental reason is insufficient efficiency of sunlight-to-energy conversion devices manufactured from inexpensive materials thus preventing large scale uptake. Along with thermal and photoelectrochemical sunlight-to-energy conversion, photovoltaics--an approach of converting sunlight directly into electricity--is probably most mature for contributing to the increasing renewable energy use. This review details the general operating principles of the main types of photovoltaic devices, device efficiencies and the limitations of each technology with due consideration of the commercial requirements and uptake within the global renewable energy sector. There is also a section dedicated to emerging research, particularly within the European academic research base, focussing on overcoming some of the limitations associated with current photovoltaic technology.