Programmable Bipolar Photocurrents in Water-Templated Nanoporous Ferroelectrics for Filter-Free Spectral Recognition

Bipolar current devices hold promise for next-generation electronics, as the additional degree of freedom in current direction enables multistate logic, adaptive sensing, and reconfigurable circuits beyond the binary paradigm. However, their practical implementation in ferroelectrics has been constrained, since polarization switching typically requires an external power supply, restricting zero-bias devices to unidirectional carrier transport and thereby limiting versatility. Here, we report a water-templated strategy for fabricating nanoporous Bi_0.5Na_0.5TiO₃ (BNT) films with uniform and tunable pore architectures. By coupling photovoltaic and thermoelectric effects, the devices exhibit wavelength-dependent polarity reversal, producing positive photocurrents at 405 nm and negative photocurrents at 785 nm. The polarity-reversal threshold is programmable through pore density, overcoming the intrinsic unipolarity of zero-bias ferroelectric devices. Integrated into a monolithic platform, these porous devices simultaneously discriminate optical wavelength and intensity through polarity-encoded outputs, establishing a foundation for biomimetic vision systems and ternary light-controlled logic.