Surface Defects Passivation with Organic Salt for Highly Stable and Efficient Lead-Free Cs₃Sb₂I₉ Perovskite Solar Cells

Poor stability and high toxicity are the primary challengestothe further development of Pb-based perovskite solar cells. To thisend, the scientific community has paid increased attention to lead-freeperovskites such as cesium antimony iodide (Cs3Sb2I9), which have demonstrated high stability. However,the charge recombination that arises from deep-level defects in Cs3Sb2I9-based solar cells results in lowpower conversion efficiencies (PCEs). Therefore, adding passivationor additives such as triiodide ions (I-3 (-)) could be viable for achieving homogeneous, compact, and defect-freeperovskite films. Herein, we develop a facile approach for eliminatingsurface defects in Cs3Sb2I9 solarcells. Light irradiation of formamidinium iodide (FAI), the generatedFA(+) and I-3 (-) ions, improvesthe grain size, crystallinity, and surface morphology of the film,thus decreasing the nonradiative defects in films. Furthermore, ahigh-quality Cs3Sb2I9-based perovskite-layeredphase is achieved at a low temperature (>100 & DEG;C). With a hole-transportlayer-free architecture (glass/FTO/c-TiO2/Cs3Sb2I9/Au, where FTO = fluorine-doped tin oxide),the PCE is boosted from 1.06 to 1.76% with good long-term stabilityin an ambient environment. Additional physical characterizations evidencedthe passivation of detrimental defects, reduction of charge recombination,and efficient charge transfer, which contribute to enhanced deviceperformance. We believe such a facile approach could pave the wayfor the widespread development of highly stable Pb-free perovskitesolar cells.