Designing Heterovalent Substitution with Antioxidant Attribute for High-Performance Sn-Pb Alloyed Perovskite Solar Cells

All-perovskite tandem solar cells are promising for breaking through the single-junction Shockley-Queisser limit, and that potentially raises interest in configuring efficient Sn-Pb alloyed narrow-bandgap perovskite solar cells (PSCs). However, the Sn-Pb alloyed perovskites are commonly plagued by uncontrollable crystallization dynamics and severe p-doping levels. Herein, an effective additive molecule is designed with heterovalent substitution and antioxidant functions, whereby an organic metal coordination compound of tris(2,4-pentanedionato)gallium (TPGa) is employed to upgrade the quality of perovskite films. Ga3+ substitution obviously boosts the formation energy of Sn vacancies and heals the trap states. Meanwhile, the crystal structure evolution process is improved by the anchoring effect of 2,4-pentanedionato. The PSCs incorporating these improvements deliver not only a power conversion efficiency of 21.5% but also outstanding stability, as demonstrated by retaining 80% of the initial efficiency for over 1500 h. In addition, 23.14%-efficient all-perovskite tandem solar cells are further obtained by pairing this PSC with a wide-bandgap (1.74 eV) top cell. This study supports the feasibility of doping trivalent ions into the Sn-Pb alloyed perovskites to compromise the self-p-doping effect and highlights the importance of acetylacetone for passivating defects and hindering oxidation.