A Bifunctional Carbazide Additive For Durable CsSnI3 Perovskite Solar Cells

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 )2 SnX3 ) 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.