Fabrication of p-type BaCuSF and n-type In2O3:Sn bilayer films and their applications to the back contact of CdS/CdTe solar cells

Abstract

For applications to polycrystalline thin-film tandem solar cells, we studied p-type conductive BaCuSF single layer and p-type BaCuSF and n-type In2O3:Sn (ITO) bilayer films. The BaCuSF films were prepared by pulsed laser deposition (PLD), and the ITO films were prepared by RF sputtering. The bilayer film showed ohmic current–voltage characteristic. A tunnel junction between these two layers was successfully fabricated, because p-type BaCuSF and n-type ITO layers had sufficiently high carrier concentrations. The BaCuSF/ITO bilayer films were employed as the back electrodes of CdS/CdTe solar cells. A CdTe solar cell with a 20-nm-thick BaCuSF/a 300-nm-thick ITO bilayer back contact showed a high conversion efficiency of 13.9% (VOC = 818 mV, JSC = 25.2 mA/cm2, and FF = 0.675), which was higher than that of a CdTe solar cell with a BaCuSF single-layer back contact (11.1%). The efficiency is comparable to that of a CdTe solar cell with a SrCuSeF/ITO bilayer back contact (14.3%).