Ge-doped Sn-Pb assisted by MACl triple metal cation perovskite solar cells with high open-circuit voltage

[Display omitted] •We report Sn-Pb-Ge triple metal cation perovskite solar cells (PSCs) for the first time.•The MACl additive completely dissolves Ge and enables Sn-Pb-Ge perovskite.•MACl and Ge compounds form complexes, improving the stability of the precursor solution.•The optimal triple metal cation PSC exhibits an open-circuit voltage of 0.834 V. The potential to achieve the best photovoltaic properties by incorporating Ge into Sn-Pb-based perovskites (PVKs) is theoretically plausible. However, practical implementation is hindered by critical obstacles associated with Ge-containing precursors, such as poor solubility and extremely low stability. Furthermore, the application of Ge in PVKs is limited, particularly when combined with Sn-Pb-based PVK, owing to the instability of Sn and Ge within the same precursor. Herein, we report a groundbreaking method for inserting Ge into Sn-Pb PVK using volatile additives, resulting in high-performance Sn-Pb-Ge triple metal cation PVK solar cells (PSCs). Adding methylammonium chloride facilitates the dissolution of germanium iodide (GeI2) through anion exchange in the precursor, which evaporates during high-temperature annealing after the formation of the PVK films. The resulting low-bandgap PVK (1.228 eV), containing 3 % Ge, exhibits increased grain sizes and a significantly improved open-circuit voltage of 0.834 V, which can be attributed to a reduced energetic offset. The Sn-Pb-Ge triple metal cation PSC exhibits a power conversion efficiency of 20.7 % and enhanced stability.