Effect of Alkali-Metal Additive on Rudorffite AgBiI₄-Based Pb-Free Solar Cells

Rudorffite material, silver bismuth iodide, is one of the promising lead-free alternatives for photovoltaic applications due to its high absorption coefficient, low toxicity, and relatively better stability. Here, we report on the effects of alkali halide additive in the absorber material AgBiI4, focusing on its material properties and solar cell devices. The inclusion of NaI significantly improved the film quality with compact and pinhole-free morphology and better crystallinity. The device with rudorffite material with NaI additive demonstrated a notable increase in the PCE from 1.33 to 3.72%, along with improved device stability. The device analysis confirmed that NaI incorporation in AgBiI4 modulates the optoelectronic quality, effectively suppressing charge recombination and enhancing charge extraction within the device. Thus, this work corroborates that additive engineering is an effective strategy for improving both the efficiency and stability of AgBiI4-based rudorffite solar cells, underscoring their potential in sustainable photovoltaic applications.