Coupling solar into metal-air batteries represents an appealing paradigm for storing intermittent solar energy and boosting device energy efficiency. Current solar-coupled metal-air systems rely on UV or visible light harvesting and suffer from inferior charge separation ability and limited solar utilization. Additionally, sunlight action behavior/mechanism in some useful scenarios (seawater electrolytes, low-temperature) is underexplored. Herein, through gradient homojunction design via donor-acceptor (D-A) engineering, it exploits a novel full-spectrum-responsive polymer homojunction photoelectrode (PGH) for sunlight-coupled seawater-electrolyte-based Zn/Na-air batteries (Zn-SWAB/Na-SWAB) with boosted sunlight utilization and energy efficiency at lower temperatures. By stacking three pre-designed analogous [A