Perovskite solar cells (PSCs) employing organic-inorganic hybrid lead perovskite have attracted much attention as promising next generation solar cells because of their low fabrication cost and extremely high power conversion efficiency (PCE). Exploring new perovskite materials and additives is one of the effective strategies to improve the performance of PSCs. Here, we synthesized formamide iodide (FoAI) and applied it as both a cation material and additive. Although it was revealed that FoAI is not incorporated in the A-site of the perovskite structure, we found that the FoAI additive suppresses δ-FAPbI3 formation and improved the performance of FAPbI3 based PSCs. The PCE was improved from 12.29% to 14.49% by adding 5 mol% of FoAI in the precursor solution. Meanwhile, we found that FoAI additive can also improve the performance of triple-cation PSCs. We believe that FoAI is one of the promising additives to boost the PCE of PSCs without any influence on the composition of the perovskite materials.
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