Enhanced Optoelectronic Properties of Cs₃Sb₂I₉ Perovskite Solar Cells through Sulfonium-Based Treatment

Lead halide perovskites are renowned for their remarkable photophysical properties, making them prime candidates for advanced optoelectronic devices. However, the toxicity of lead is motivating research of lead-free perovskites using environmentally friendly alternatives for safer photovoltaic applications. Here, we investigate cesium antimony iodide (Cs3Sb2I9) perovskite-inspired material (PIM) as a lead-free option. A key limitation in the solar cell performance of this PIM is trap-assisted nonradiative recombination at the perovskite/hole transporting layer interface. We report an effective surface passivation strategy using dimethyl phenethyl sulfonium iodide (DMPESI). This approach significantly reduces surface defect density, minimizes nonradiative recombination, and enhances charge carrier transport. The optimized DMPESI-modified perovskite films achieved a power conversion efficiency of 2.63%, with an open-circuit voltage of 0.80 V, a short-circuit current density of 4.57 mA cm–2, and a high fill factor of 0.72, representing one of the highest device performances reported to date for Cs3Sb2I9. Furthermore, the passivated devices demonstrated improved operational stability. Photocurrent spectra suggest that short electron diffusion length in Cs3Sb2I9 is another limiting factor for these devices. These findings offer valuable insights into surface engineering techniques that could enhance the performance of lead-free photovoltaic devices, suggesting that antimony-based Cs3Sb2I9 holds substantial potential for future environmentally friendly photovoltaic applications.