Extending Absorption of Cs2AgBiBr6 to Near-Infrared Region (approximate to 1350 nm) with Intermediate Band

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 approximate 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.