To capture the essence of the rapid progress in optical engineering exploited in high-performance polymer solar cells (PSCs), a comprehensive overview focusing on recent developments and achievements in PSC electrode engineering is provided in this review. To date, various kinds of electrode materials and geometries are exploited to enhance light-trapping in devices through distinct optical strategies. In addition to the widely used nanostructured electrodes that induce plasmonic-enhanced light absorption, planar ultra-thin metal films also have attracted significant attention due to their remarkably reflective transparent properties that beget efficient optical microcavities. These microcavities confine incident light with resonant frequencies between two reflective electrodes due to optically coherent interference, boosting the light absorption of thin-film PSCs while maintaining efficient charge dissociation and extraction. After reviewing the challenges in developing high-performance microcavity-enhanced PSCs (MCPSCs), we discuss strategies to improve MCPSC performance further to showcase the potential of harnessing microcavity resonance effects in thin-film PSCs.