Modeling and optimization of CZTS kesterite solar cells using TiO2 as efficient electron transport layer

In this paper, a numerical simulation study via AMPS 1D simulator is carried out to investigate the degradation mechanisms occurred in hybrid Cu2(Zn,Sn)Se4 (CZTS) solar cells that use a nonporous n-type-TiO2 material as a window. The advantageous Spike-like conformation against recombination at the TiO2/CZTS interface, which is ensured by the band-engineering offset established using TiO2 material, is discussed. The influence of the geometrical and physical parameters on the device fundamental figures of merit is assessed. Besides, the degradation effect linked to both deep and tail states situated in the gap of the materials, and the effective working temperature, are taken into account. The results reveal that the actual defect type (donor or neutral) at the Cu2ZnSnS4 layer has a harsh influence on the device performance. This is attributed to the raised Shockley–Read–Hall (SRH) recombination highlighted by investigating the variation of the carrier density along the absorber layer. A low barrier height at the back contact (ϕbl = 0.1 eV) and a suitable doping level and thickness of both the window (ND = 4 × 1017 cm−3, WTiO2 = 0.02 µm) and the absorber (NA = 6.5 × 1016 cm−3, WCZTS = 3.2 µm) layers could efficiently improve the device performance.