Ligand‐Anchoring‐Induced Oriented Crystal Growth for High‐Efficiency Lead‐Tin Perovskite Solar Cells

Abstract The narrow bandgap (≈1.2 eV) Pb‐Sn alloyed perovskite solar cell is a promising bottom component cell for all‐perovskite tandem devices that are expected to offer higher efficiency than the theoretical Shockley–Queisser limit of the single‐junction solar cells. The density functional theory (DFT) study reveals that the Pb‐Sn perovskite film with the (100) orientation would render significantly reduced trap density, which is a critical figure‐of‐merit for perovskite device performance. Alkyl diamine is therefore designed to first anchor onto the surface as a nucleation agent to modulate the Pb‐Sn perovskite growth to proceed preferentially along with the (100) orientation. It is observed that the diamine cations not only effectively induced the crystal growth at the nucleation stage, but also remained on the crystal surface to eventually passivate the resultant perovskite film. As a result, the diamine‐based films show (100) preferred orientation with superior optoelectronic properties, as predicted by the DFT investigation. Consequently, the champion power conversion efficiency of 20.03% is achieved, one of the highest for this type of device. These findings provide a practicable strategy to theoretically design surface nucleation to induce preferential growth of perovskite material for better optoelectronic performance.