The flexo-photovoltaic (FPV) effect, whereby the induction of a bulk photovoltaic response by a strain gradient, offers a promising mechanism for advanced optoelectronics beyond conventional material symmetries. Here, a pronounced FPV effect in the piezoelectric Janus ${\mathrm{In}}_2\mathrm{STe}$ monolayer is reported based on first-principles calculations, where the electronic structure and polarization are exquisitely sensitive to strain gradients. The exceptional flexibility (35.23 N/m), combined with a high out-of-plane piezoelectric coefficient (0.24 pm/V) and a substantial flexoelectric coefficient (4.58 nC/m), underpins strong electromechanical coupling. We harness this to create a polarization-sensitive photodetector that exhibits a self-powered photocurrent via FPV effect, amplified by nearly two orders of magnitude through synergistic piezoelectric-flexoelectric coupling. This coupling can be tuned to a competitive regime, yielding a distinct self-rectifying state. Finally, we integrate these effects to demonstrate dynamic control over photo-carriers, enabling a trichannel optical communication system with enhanced data density. This work establishes a versatile multifunctional coupling architecture for a new generation of intelligent flexible optoelectronics.

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• Flexoelectricity
• Optoelectronics
• Photocurrent
• Piezoelectricity
• Flexible electronics
• Janus materials
• Density functional theory
• First-principles calculations