We report the observation of persistent photoconductivity in $n$-type chlorine-doped ${\mathrm{Sb}}_2{\mathrm{Se}}_3$ single crystals, which exhibit free carrier concentrations exceeding ${10}^{16}{\mathrm{cm}}^{-3}$ at room temperature. Illumination with band gap or near-band gap light below $\sim 30\mathrm{K}$ induces photoconductivity that endures for hours after light cessation. This effect is accompanied by a strongly polarized infrared absorption along the covalently bonded $\mathrm{Sb}-\mathrm{Se}$ chains, following a spectral power-law dependence ${\omega }^{-n}$, where $n$ ($2.2-3.2$) depends on sample and illumination conditions, consistent with band-like transport. Both persistent photoconductivity and photoinduced absorption vanish above $\sim 40\mathrm{K}$ due to a thermal barrier of approximately $190\pm 20\mathrm{meV}$. These phenomena are absent in undoped or O- and Sn-doped samples, underscoring the pivotal role of chlorine doping in enabling persistent photoconductivity.

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• Charge dynamics
• Defects
• Doping effects
• Electrical conductivity
• Electrical properties
• Photoconductivity
• Photoinduced effect