Lead-free perovskite Cs2AgBiBr6 manifests great potential in developing high-performance, environmentally friendly, solution-processable photodetectors (PDs). However, due to the relatively large energy bandgap, the spectrum responses of Cs2AgBiBr6 PDs are limited to the ultraviolet and visible region with wavelengths shorter than 560 nm. In this work, a broadband Cs2AgBiBr6 PD covering the ultraviolet, visible, and near infrared (NIR) range is demonstrated by incorporating titanium nitride (TiN) nanoparticles that are prepared with the assistance of self-assembled polystyrene sphere array. In addition, an atomically thick Al2O3 layer is introduced at the interface between the Cs2AgBiBr6 film and TiN nanoparticles to alleviate the dark current deterioration caused by nanoparticle incorporation. As a result, beyond the spectrum range where Cs2AgBiBr6 absorbs light, the external quantum efficiency (EQE) of the TiN nanoparticle incorporated Cs2AgBiBr6 PD is enhanced significantly compared with that of the control, displaying enhancement factors as high as 2000 over a broadband NIR wavelength range. The demonstrated enhancement in EQE arises from the photocurrent contribution of plasmonic hot holes injected from TiN nanoparticles into Cs2AgBiBr6. This work promotes the development of broadband solution-processable perovskite PDs, providing a promising strategy for realizing photodetection in the NIR region.