Organic n-Type Molecule Mediated Crystallization Regulation for Sn-Pb Perovskite Solar Cells

Narrow-bandgap Sn-Pb perovskites have showcased great potential for constructing tandem perovskite solar cells (PSCs). However, Sn^{2 +} in Sn-Pb PSCs is readily oxidized to Sn^{4 +}, and such B-site Sn^{4 +} will introduce excess positive charge and causes severe p-type self-doping, which pins the Fermi level and aggravates non-radiative recombination. Additionally, the Sn-based component crystallizes far more rapidly than that of Pb, resulting in unbalanced Sn-Pb crystallization. To address these challenges, we develop a novel n-type molecule NDBH as perovskite additive. This molecule offers three key advantages: prevents the oxidation of Sn^{2 +} through chelation and blocks oxygen ingress along grain boundaries; balances the crystallization rates of Sn-Pb perovskite by selectively chelating Sn^{2 +}; modifies the perovskite surface to be more n-type. With this organic n-type molecule, the inverted Sn-Pb PSCs achieve power conversion efficiency (PCE) of 24.11%. The devices also exhibited remarkable long-term stability, retaining over 90% of their initial efficiency after 600 h of maximum power point (MPP) tracking. This approach of designing multifunctional n-type molecules offers a new perspective for enhancing the efficiency and stability of Sn-Pb PSCs.