Low‐Melting‐Point Alloys for Printable Rear Electrodes in Perovskite and Organic Solar Cells: A Review

ABSTRACT

Noble‐metal rear electrodes deposited by high‐vacuum thermal evaporation impose a major bottleneck for the development of perovskite solar cells (PSCs) and organic solar cells (OSCs), owing to high material costs, unstable interfaces, and poor manufacturability. Low‑melting‑point alloys (LMPAs) represent a versatile alternative rear‑electrode candidate that supports direct patterning under low‑temperature, vacuum‑free conditions. Upon ambient air exposure, LMPAs spontaneously develop an in‑situ surface oxide layer, which can mitigate Schottky‑barrier effects to facilitate efficient charge extraction and suppress ion/atom migration to improve device stability. In addition, the intrinsic mechanical compliance and self‑healing capacity of LMPAs render them particularly promising for flexible and stretchable photovoltaic devices. This timely review first introduces fundamental properties of LMPAs and their unique merits for photovoltaic applications. Recent advances in LMPA rear electrodes for OSCs and PSCs are reviewed, with focused emphasis on fabrication strategies for finely patterned LMPA electrodes. We thoroughly discuss the critical functions of the in‑situ oxide layer, alongside the mechanical advantages of LMPAs for bendable and stretchable devices. Design principles and performance trade‑offs are then summarized. Finally, remaining challenges and future research opportunities for LMPA‐electrode‐based solar cells are highlighted.