Extending Absorption of Cs₂AgBiBr₆ to Near‐Infrared Region (≈1350 nm) with Intermediate Band

Abstract The toxicity of lead‐based halide perovskites hampers broad application in optoelectronics. Lead‐free perovskite Cs₂AgBiBr₆ is considered a promising candidate, owing to the long carrier lifetime and great stability. However, the relatively large bandgap of 1.98 eV limits its absorption in the visible region. Herein, Fe²⁺ is chosen as the dopant to alloy into Cs₂AgBiBr₆ single crystals, and results in an absorption range broadening to ≈1350 nm, which is the longest near‐infrared (NIR) response recorded among lead‐free perovskites. About 1% of Fe ions are alloyed into the Cs₂AgBiBr₆ lattice to cause lattice shrink age. Instead of narrowing the bandgap, Fe doping would introduce a new intermediate band inside the pristine bandgap of Cs₂AgBiBr₆ to strongly absorb NIR light, as confirmed by third harmonic generation results. Moreover, considerable photogenerated carriers are produced in Fe doped Cs₂AgBiBr₆ crystals with NIR irradiation. This work has provided a new way to extend the optical response of lead‐free perovskites for NIR photodetectors and intermediate band photovoltaics.