Transient Absorption Spectroscopy of NbOI2.

NbOI2 has recently emerged as a new van der Waals material combining semiconducting behavior with intrinsic in-plane ferroelectricity and pronounced transport and optical anisotropy. However, its photocarrier dynamics remain largely unexplored. Here, we report transient absorption spectroscopy of NbOI2 using femtosecond pump-probe measurements. A pronounced transient absorption feature is observed near the 2.34 eV excitonic resonance, arising from photocarrier-induced excitonic energy shifts and saturation. The decay dynamics reveal an exciton lifetime of several tens of picoseconds. The observed density-dependent behavior is consistent with exciton-exciton annihilation and defect-assisted Auger recombination, yielding a rate of 0.4 cm2 s-1. Polarization-resolved measurements further reveal a pronounced in-plane anisotropy in the transient response that follows the linear absorption anisotropy. These findings provide fundamental insight into photocarrier dynamics in NbOI2 and establish key parameters for understanding and exploiting its optoelectronic behavior.