Improving Open-Circuit Voltage in Cu₂ZnSnSe₄ Thin Film Solar Cells Via Interface Passivation

Abstract

The earth-abundant Cu2ZnSnSe4 (CZTS) thin film solar cells have demonstrated promising results with the record power conversion efficiency of 12.6%. However, they suffer from the high open-circuit voltage (Voc) deficit that hinders further improvement in the device performance. Ongoing studies regarding the origins behind this critical issue suggest that it stems from the fluctuation of band structures and non-radiative recombination centers in CZTS solar cells. Here, we focused on passivating the interfaces of CZTS solar cells – both a front CdS/CZTS interface and a back CZTS/Mo interface – to reduce the interfacial recombination that may greatly contribute to a large Voc deficit of CZTS solar cells. By applying a thin dielectric on top of the CZTS and a nano-patterned dielectric layer between the CZTS and the Mo, Voc is significantly enhanced; the Voc-deficit value is comparable to that of the world record CZTS solar cell. Structural and electrical properties of the CZTS devices with passivation layers were studied using scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, J-V and external quantum efficiency measurement, low-temperature photoluminescence, and time-resolved photoluminescence analysis. The effects of interface passivation in correlation with the device performance will be presented as well.