Effect of wide band-gap TCO properties on the bifacial CZTS thin-films solar cells performances

In this work, one-dimensional device simulator AMPS-1D was employed to study the electrical and optical properties of bifacial ZnO:Al/CdS/Cu2ZnSnS4 (CZTS)/TCO/SLG thin film solar cells. The impact of barrier height in the CZTS/TCO interface has been investigated for front and back side illuminations. The combination of the optical transparency and the electrical properties for the TCO back contact layer are capable of yielding high efficiency. The presence of barriers in the CZTS/TCO back-side interface of the structure can significantly affect the cell performance by limit the carriers current flow. The optimum CZTS absorber layer thickness used in the simulation has been calculated. The best energy conversion efficiency has been calculated in the case of front and back side illuminations. In the case of front side illumination, an efficiency of 15.8% (with Voc ≈ 0.93 V, Jsc ≈ 18.7 mA/cm2, FF ≈ 0.77 and QE ≈ 82.5% at 570 nm) have been obtained with a barrier height close to 0.4 eV. In the case of back side illumination, we notice a low performances. For 0.4 eV barrier height, we obtain 1.8% (with Voc ≈ 0.95 V, Jsc ≈ 2.6 mA/cm2, FF ≈ 0.74 and QE ≈ 20.6% at 820 nm). Without barrier height we obtain a maximum of efficiency (η ≈ 4%) in the case of back side illumination. All these simulation results give some important indication to lead a higher efficiency of bifacial CdS/CZTS/TCO structure for feasible fabrication.