Energy Band Alignment in Molybdenum Oxide/Cu(In,Ga)Se₂ Interface for High-Efficiency Ultrathin Cu(In,Ga)Se₂ Solar Cells from Low-Temperature Growth

In this work, the molybdenum oxide (MoOx) was employed as a back contact layer to improve the device performance of ultrathin Cu(In,Ga)Se2 (CIGS) solar cells with CIGS absorber synthesized through the low-temperature three-stage co-evaporation process. This contribution focuses on the investigation of the inherent mechanisms and the improved device performance in detail. Our research shows that the energy band of the CIGS/Mo interface can be tuned and the Schottky barrier can be reduced. Compared with the reference sample without MoOx, the back barrier height of the new device with 10 nm MoOx enjoys a significant decrease from 43.83 to 15.98 meV because of the improvement of energy band structure. Meanwhile, the results of wxAMPS simulation corroborate that the energy band bends upward in the devices with an appropriate thickness of MoOx films, which facilitates the carrier transportation and suppresses the recombination of charge carriers at the MoOx/Cu(In,Ga)Se2 interface. Moreover, the carriers can transport through the MoOx/CIGS interface by tunneling when the MoOx film is thin enough. Finally, by controlling the thicknesses of MoOx films, an efficiency of 10.38% is achieved in 0.5 μm CIGS solar cells by optimizing the MoOx thickness under the low-temperature three-stage co-evaporation process.