Simultaneous Effective Chemical and Field Passivation at Back Interface of CdTe Solar Cells Using Copper Indium Oxide

Back surface engineering is one of the ways to further improve the conversion efficiency of the CdTe solar cells. In this work, as an oxide mixture, Cu x In y O is synthesized by low-temperature solution processing and successfully applied to the CdTe solar cells in the form of amorphous nanoparticles. The XPS results reveal changes in the chemical states of Te and O, and the KPFM demonstrate that a ∼350 mV electric field has been introduced at the CdTe back surface, which means effective chemical passivation and field passivation were induced, resulting in the suppression of carrier recombination and the increase of carrier lifetime at the back interface of the devices. Finally, compared to the control devices, the conversion efficiency of the devices with Cu x In y O buffer layer improved from 12.44% to 15.35%, attributed to the increase in the fill factor from 65.52% to 72.48% and the open-circuit voltage from 723 mV to 798 mV.