Characterisation of multi-junction solar cells by mapping of the carrier transport efficiency using luminescence emission

Multijunction solar cells are currently the devices offering the largest conversion efficiencies of the solar radiation, which could be further increased by limiting their series resistances. A clear evaluation of the impact of those resistances is therefore required, and provided in this paper by introducing a mapping method of the current transport efficiency from luminescence images. This method brings finer information on the cell than electroluminescence methods, widely used so far for multi-junction cells, and offers much faster acquisition time than what could be obtained with a light beam induced current setup. While it has been theoretically and experimentally developed for single junction solar cells, its application to multijunction cells remains to be demonstrated. The purpose of this communication is to assess its validity and to explain some results that can be counterintuitive at a first sight. Two different triple-junction architectures are investigated and successfully compared with electrical measurements and calculations.