Palladium‐Doped Cs2AgBiBr6 with 1300 nm Near‐Infrared Photoresponse

Lead‐free halide double perovskite (HDP) Cs2AgBiBr6 has set a benchmark for research in HDP photoelectric applications due to its attractive optoelectronic properties. However, its narrow absorption range is a key limitation of this material. Herein, a novel dopant, palladium (Pd), is doped into Cs2AgBiBr6 and significantly extends the absorption to ≈1400 nm. Pd2+ ions are partially doped in the host lattice, most probably replacing Ag atoms and introducing a sub‐bandgap state within the host bandgap, as indicated by the combination of spectroscopical measurements and theoretical calculations. Importantly, this sub‐bandgap state extends the photoresponse of Cs2AgBiBr6 up to the NIR‐II region of 1300 nm, setting a new record for HDPs. This work demonstrates a novel and efficient dopant for HDPs and highlights the effectiveness of employing a sub‐bandgap to broaden the absorption of HDPs, shedding new light on tailoring large bandgap HDPs for NIR optoelectronic applications. A novel dopant of Pd is introduced into lead‐free Cs2AgBiBr6 double perovskite. Pd2+ enters the lattice of Cs2AgBiBr6, substitutes the crystallographic position occupied by Ag+, and forms a sub‐bandgap energy level in the host material. Pd‐doped Cs2AgBiBr6 shows significantly extended absorption to ≈1400 nm and NIR light response up to 1300 nm.