Perovskite Quantum Dot Surface Engineering for High-Efficiency and Stable Tin-Lead Perovskite Solar Cells

Owing to their exceptional optoelectronic efficiency and adjustable bandgaps, perovskite materials have emerged as promising candidates for next-generation optoelectronic devices, including solar cells, LEDs and photodetectors. Nevertheless, state-of-the-art perovskite solar cells (PSCs) predominantly rely on lead, raising critical concerns regarding ecological and human toxicity. To mitigate this toxicity while maintaining a narrow bandgap for broad-spectrum light absorption, tin-lead (Sn-Pb) mixed PSCs have been developed through partial tin substitution. However, the severe environmental vulnerability of tin leads to rapid device degradation, posing a significant hurdle to practical applications.
Herein, we demonstrate a strategic approach to boost both the efficiency and operational stability of Sn-Pb PSCs through targeted surface engineering using a perovskite quantum dot (PQD) coating layer. Specifically, CsPbI₃ and CsSn_0.4Pb_0.6I₃ PQDs were prepared via a conventional hot-injection route. While CsPbI₃ suffers from noticeable lattice distortion induced by the large ionic radius of Pb, the partial replacement of Pb with smaller Sn ions in CsSn_0.4Pb_0.6I₃ effectively alleviates this structural strain. To overcome the charge transport barriers typically imposed by long-chain insulating ligands on PQD surfaces, a polar solvent washing step using isopropyl alcohol was implemented. This treatment induces ligand dissociation to passivate defects on the underlying Sn-Pb film, while the liberated ions from the PQDs function as beneficial chemical constituents. Finally, the physiochemical and optoelectronic properties of these Sn-Pb mixed PQDs are comprehensively evaluated and contrasted with standard lead-based counterparts.