Lewis Base–Zwitterion Dual Additives Enable Efficient Blade-Coated Tin-lead Perovskite Solar Cells and Tandems

High-efficiency all-perovskite tandem solar cells are severely constrained by narrow-bandgap Sn-Pb subcells, which confront an inherent contradictory bottleneck: Sn 2+ -rich precursors undergo fast, unregulated crystallization during blade coating, yet Sn 2+ cations are easily oxidized to harmful Sn 4+ under ambient conditions. Conventional single additive materials can only address one of the two critical drawbacks instead of balancing both. Herein, we develop a dual-additive strategy combining Lewis-base amidinothiourea (FATU) and zwitterionic glycine hydrochloride (GlyHCl) with two core synergistic functions. FATU utilizes C═S and −NH 2 groups to preferentially chelate Sn 2+ , inhibiting its oxidation and pre-nucleation aggregation; GlyHCl simultaneously coordinates Pb 2+ and Sn 2+ to slow global crystallization kinetics and suppress heterogeneous nucleation. This dual synergy fabricates high-quality Cs 0.1 FA 0.5 MA 0.4 Pb 0.5 Sn 0.5 I 3 films with over 800 nm large grains and minimized trap density. The blade-coated single-junction device reaches 21.02% PCE with V OC boosted from 0.797 to 0.850 V. When integrated with a 1.76 eV wide-bandgap top cell, the tandem achieves 27.84% peak efficiency (stabilized at 27.33%) and retains more than 75% initial efficiency after 680 h continuous MPP tracking. This work offers a practical pathway for scalable blade-coating production of high-performance all-perovskite tandem photovoltaics.