Micro-concentrated photovoltaics based on Cu(In,Ga)Se2 microcells: an optical study Ning Li, Chao Wang, Ye Tu, Jinming Zhang and Guanchao Yin Eur. Phys. J. Appl. Phys., 97 (2022) 1 Published online: 13 January 2022 DOI: 10.1051/epjap/2021210215