Efficiency boost of CZTS solar cells based on double-absorber architecture: Device modeling and analysis

In this study, we present a new alternative approach that utilizes Si as a second absorber along with the primary CZTS absorber to improve all photovoltaics performance parameters for CZTS based thin-film solar cell devices. The proposed ZnO:Al/CdS/CZTS/Si/Mo with a double-absorber hybrid structure has been extensively investigated and analyzed by employing the SCAPS-1D simulation package. Initial direct integration of a thin Si layer with thickness as low as 200 nm between the Mo back-contact and the primary CZTS active layer has resulted in a significant efficiency boost of 16.32%. Further optimization of several material parameters such as thickness, bandgap energy, and doping concentration for both absorbers have resulted in additional enhancement of many photovoltaic performance parameters such as the FF, J(sc,) V-oc,V- and PCE. The correlation study between the two absorbers suggests that maximum efficiency of 19.40%, FF of 88.54%, V-oc of 0.84 V and J(SC) of 27.55 mA/cm(2) can be attained at absorbers thicknesses of about 2 mu m and high doping level up to 10(18) cm(-3) . This can be attributed to the generation of more charge carriers with the increase of absorbers thicknesses. Additionally, the proposed model shows a stable performance with the rise of the operating temperature up to 350 K. Adding Si layer to the cell structure has resulted in pronounced quantum efficiency (QE) improvement due to the increase of solar spectrum absorption at longer wavelengths. A significant improvement in I-V characteristics was also detected with the decrease of the double-absorber structure's series resistance compared to the conventional single-absorber CZTS structure. The outcomes of this study represent a promising solution toward the fabrication of high-performance and cost-effective thin CZTS solar cell devices.