A Bifunctional Carbazide Additive For Durable CsSnI₃ Perovskite Solar Cells

Abstract Inorganic CsSnI₃ with low toxicity and a narrow bandgap is a promising photovoltaic material. However, the performance of CsSnI₃ perovskite solar cells (PSCs) is much lower than that of Pb‐based and hybrid Sn‐based (e.g., CsPbX₃ and CH(NH₂)₂SnX₃) PSCs, which may be attributed to its poor film‐forming property and the deep traps induced by Sn⁴⁺. Here, a bifunctional additive carbazide (CBZ) is adapted to deposit a pinhole‐free film and remove the deep traps via two‐step annealing. The lone electrons of the NH₂ and CO units in CBZ can coordinate with Sn²⁺ to form a dense film with large grains during the phase transition at 80 °C. The decomposition of CBZ can reduce Sn⁴⁺ to Sn²⁺ during annealing at 150 °C to remove the deep traps. Compared with the control device (4.12%), the maximum efficiency of the CsSnI₃:CBZ PSC reaches 11.21%, which is the highest efficiency of CsSnI₃ PSC reported to date. A certified efficiency of 10.90% is obtained by an independent photovoltaic testing laboratory. In addition, the unsealed CsSnI₃:CBZ devices maintain initial efficiencies of ≈100%, 90%, and 80% under an inert atmosphere (60 days), standard maximum power point tracking (650 h at 65 °C), and ambient air (100 h), respectively.