Advanced light manipulation is extremely attractive for applications in organic optoelectronics to enhance light harvesting efficiency. A novel method of fabricating high-efficiency organic solar cells (OSCs) is proposed using biomimetic moth eye nanostructures in a quasi-periodic gradient shape active layer and an antireflective coating. A 24.3% increase in photocurrent is realized without sacrificing dark electrical properties, yielding a 22.2% enhancement in power conversion efficiency to a record of 7.86% for OSCs with a poly(3-hexylthiophene-2,5-diyl):indene-C60 bis-adduct (P3HT:ICBA) active layer. The experimental and theoretical characterizations verify that the substantial improvement of OSCs is mainly ascribed to the self-enhanced absorption resulting from the broadband polarization-insensitive light trapping in biomimetic nanostructured active layer, the reduction in reflectance by the antireflective coating, and surface plasmonic effect excited by corrugated metallic electrode. It is noteworthy that the pathway described here is promising for opening up opportunities to realize high-performance OSCs towards the future photovoltaic applications.