Uncovering the underlying electromagnetic mechanism of lead-free all-perovskite tandem solar cells with ZnO moth-eye antireflection layers

As the push to enhance power conversion efficiency (PCE) in solar cells intensifies, tandem configurations that integrate photovoltaic devices with complementary bandgaps have become essential. Perovskite materials are particularly advantageous in these tandem solar cells due to their adjustable bandgaps (ranging from 1.2 to 2.2 eV), superior light absorption, remarkable structural stability, and efficient charge-carrier mobility. Lead-free perovskites offer the benefits of traditional perovskites while also being nontoxic and stable; thus, they are ideal candidates for tandem solar cells. However, the optical loss associated with light reflection from the upper surface of the cell degrades device performance, thus reducing the PCE of solar cells; therefore, continuous research efforts are needed to address this drawback. In this study, we coated a lead-free all-perovskite tandem solar cell with a parabolic zinc oxide (ZnO) moth-eye antireflection (AR) layer and assessed its efficiency in suppressing reflection using the two-dimensional finite-difference time-domain method. We analyzed the maximum short-circuit current density (J_sc,max) of the lead-free all-perovskite tandem solar cell by varying the height (H) of the ZnO moth-eye AR layer. Notably, for H = 300 nm, J_sc,max was about 30.5 mA/cm², which indicated that 300 nm was the optimal height for performance improvement. Moreover, we generated a profile for the light-trapping phenomenon that occurs within an actual cell by simulating the electromagnetic mechanism governing the generation rate and proportion of absorbed photons. This profile enabled us to characterize the light-trapping phenomenon within the tandem solar cell induced by the ZnO moth-eye AR layer.