Abstract: Flexible near-infrared photodetectors hold promise for applications in wearable health monitoring, curved-surface imaging, and distributed optical sensing. However, their practical implementation remains constrained by the need for external power supplies, limited mechanical adaptability, and insufficient spatial light recognition capabilities. In this work, Ag₂Se thin films were fabricated on flexible polyimide substrates via layer-by-layer deposition of Ag and Se, followed by rapid thermal annealing, to construct a zero-bias near-infrared photothermoelectric detector. The resulting film primarily consisted of β-Ag₂Se, exhibited a degree of (00 l ) preferred orientation, and demonstrated stable n-type thermoelectric behavior with a room-temperature Seebeck coefficient of approximately −105 μV·K⁻¹. Upon irradiation of opposite device ends with a 1550 nm laser, the output voltage reversed polarity, yielding an apparent voltage responsivity of approximately 50 V·W⁻¹; this behavior is consistent with a photothermoelectric-dominated response mechanism. The device maintained stable electrical responses during repeated light-switching and cyclic bending tests. Furthermore, a 6×6 flexible detector array enabled two-dimensional voltage mapping of spatial illumination patterns. These results demonstrate the potential of flexible Ag₂Se/PI devices for zero-bias near-infrared sensing and spatial optical-field detection.