Realizing SnF₂-TMAB passivated lead-free formamidinum perovskite solar cells with doctor-bladed carbon electrode

The suitable band gap with outstanding optoelectronic characteristics makes Sn-based perovskites one of the promising candidates for the preparation of efficient lead-free perovskite solar cells (PSCs). However, preparing Sn²⁺-based PSCs is very difficult due to the ready oxidation of Sn²⁺ to Sn⁴⁺ when exposed to air. In this work, by incorporating the trimethylamine borane complex (TMAB) as an antioxidant additive into the perovskite precursor solution along with excess SnF₂, we report the fabrication of air-stable FASnI₃-based solar cells. The complex formed by TMAB-SNF₂ (additive layer) enables in-situ encapsulation of perovskite grains. This layer considerably improves the oxidation stability of the perovskite layer by eliminating oxygen vacancies from the NiO hole transport. The resulting PSCs can maintain more than 70% of the efficiency over 45 and 75 hours respectively in air and N₂ exposure without encapsulation. This can be regarded as a genuinely enhanced attribute, particularly considering the use of carbon in one of the electrodes in FASnI₃ perovskites. The findings suggest an alternative approach to provide effective and sustainable Sn-based PSCs in the future.