1. Renewable energy data-Fraunhofer ISE 2016 https://www.ise.fraunhofer.de/en/renewable-energy-data/renewable-energy-data
2. CIGS White Paper Initiative-CIGS Thin-film photovoltaics http://cigs-pv.net/cigs-white-paper-initiative/
3. Effects of heavy alkali elements in Cu(In,Ga)Se2 solar cells with efficiencies up to 22.6%;Jackson;Phys Status Solidi RRL,2016
4. Solar frontier achieves world record thin-film solar cell efficiency: 22.3% http://www.solar-frontier.com/eng/news/2015/C051171.html
5. Progress in thin film CIGS photovoltaics-research and development, manufacturing, and applications;Feurer;Prog Photovolt,2016