Achievement of Graded Band Gap in CdTe Solar Cells through Selenization of the Absorber

The awareness of climate change is growing worldwide and with it, also the request for alternative energy solutions to fossil sources. Photovoltaic energy is one of the main answers, since the technology is well developed and can be installed anywhere. The main challenge in this field, today, is to reduce the costs of the energy produced. In this respect, CdTe thin film panels, which can be fabricated in a single manufacturing line, have a great advantage over traditional crystalline silicon cells. Moreover their efficiency is nowadays closer to that of silicon cells, having reached a value of 22.1 %. The efficiency improvement is mainly due to the replacement of the CdS layer with MZO, which has a higher band gap, and to the introduction of a CdTe1-xSex layer, which allows the grading of the absorber band gap, increasing the absorption in the long wavelength region. In this work we present a novel method to produce the band gap grading of the CdTe absorber layer through selenization of the CdTe layer.