Tailoring Interfaces and Crystallization via a Molecular Director in Mixed Sn–Pb Perovskites for High-Efficiency All-Perovskite Tandems

Abstract Tin–lead mixed perovskite solar cells (Sn–Pb PSCs), as a key component for all-perovskite tandem architectures, hold great promise for surpassing the efficiency limits of single-junction devices. However, the commonly used PEDOT:PSS hole transport layer (HTL) often limits the performance and stability of Sn–Pb PSCs because of its hygroscopic and acidic nature. To overcome this, we introduce a buried interface engineering strategy by incorporating two chiral molecules, namely (R)-2-amino-3-(2-hydroxyphenyl)propionic acid hydrochloride (HPA) and (R)-2-amino-3-(benzyloxy)propionic acid hydrochloride (HDS), directly into PEDOT:PSS. These additives not only mitigate hygroscopicity and improve the film uniformity of PEDOT:PSS but also effectively modify the buried interface. They regulate the quinoid structure ratio in PEDOT, optimize the HTL work function, and passivate interfacial defects, thereby enhancing charge extraction and promoting crystallization of the upper perovskite layer. As a result, the optimized devices exhibit significantly improved charge transport and suppressed carrier recombination, achieving remarkable power conversion efficiencies (PCEs) of 22.63% (HPA) and 23.23% (HDS), from a control value of 21.62%. These efficiencies are among the highest reported for Sn–Pb mixed PSCs to date and are accompanied by notably enhanced long-term stability. Furthermore, this approach enables a two-terminal all-perovskite tandem solar cell with an outstanding PCE of 28.48%, demonstrating its broad applicability to high-efficiency photovoltaic systems.