Crystallization, Properties, and Challenges of Low‐Bandgap Sn–Pb Binary Perovskites

Solution‐process and low‐temperature perovskites have motivated a broad range of interests and intensive studies for applications in solar cells (SCs) and photodetectors (PDs). Perovskite SCs with the bandgap of ≈1.5 eV currently exhibit the certified efficiency over 22% comparable with those of established thin film technologies. Meanwhile, perovskite PDs achieve superb performances in the visible region compared with commercial Si PDs. Partial substitution of Sn into Pb‐based perovskites can tune the absorption to near‐infrared (NIR) region, which would achieve an ideal‐bandgap perovskite approaching the Shockley–Queisser‐efficiency limit, low‐bandgap perovskite‐based bottom subcells in tandem devices (≈1.2 eV), and NIR photodetection. Here, various crystallization methods for growing low‐bandgap Sn–Pb binary perovskites are presented. Their impacts on morphology, crystallinity, preferred orientation, carrier lifetimes, Urbach energy, and stability of the resultant Sn–Pb binary perovskites are highlighted. Then, a description is given of single‐junction, 2‐terminal, and 4‐terminal SCs using these perovskites as absorbers, which achieve up‐to‐date efficiencies of 17.8%, 18.4%, and 21.2%, respectively. The current development of ultraviolet–visible–NIR PDs using these perovskites is also discussed. Furthermore, the challenges in controlling inter‐grain Sn/Pb element distributions and perovskite stability, which will influence performance and stability of Sn–Pb perovskite‐based devices, are presented. Finally, potential prospects are discussed for advancing low‐bandgap Sn–Pb binary perovskite‐based optoelectronic devices.