Low-Temperature Growth of Submicron Cu(In, Ga)Se2 Solar Cells Based on Molybdenum Oxide Back Interface Layer

Cu(In,Ga)Se-2 (CIGS) thin film solar cells are proven to be highly efficiency. However, lowering the substrate temperature and reducing absorber layer thickness can lead to severe light and electric losses. In this work, the authors employ molybdenum oxide acting as back interface layer in order to decrease the recombination at the rear interface in low-temperature growth of submicron CIGS solar cells. X-ray photoelectron spectroscopy (XPS) results show that the compositions of molybdenum oxide films are mainly MoOx(2 < x < 3) under the influence of metal molybdenum substrate and CIGS absorber. Meanwhile, the authors study the properties of CIGS devices with different MoOx thicknesses. They find that MoOx with appropriate thickness can facilitate the crystallization of CIGS absorber layer and restrain the recombination in the CIGS bulk as well as at the back interface. Finally a CIGS solar cell with active area efficiency of 11.8% is fabricated by low-temperature processes below 450 degrees C when the thicknesses of absorber layer and molybdenum oxide are 0.92 and 10 nm, respectively. Compared with the reference device, absolute increase about 40 mV and 13% for V-oc and FF are achieved.