Organic electronics have gained widespread interests due to their flexibility lightness and low-cost potential, as well as large-scale roll-to-roll processing. However, organic electronics require additional development before they can be fully integrated into our daily lives. To achieve feasibility for commercial use, these devices must be biocompatible and flexible, while maintaining high performance. In this paper, biocompatible silk fibroin (SF) integrates with a mesh of silver nanowires (AgNWs) to build up flexible organic solar cells with champion power conversion efficiency of up to 7.29%. The SF-AgNWs substrate exhibits a conductivity of ~11.0 Ω/sq and transmittance of ~80% in the visible light range. Surprisingly, these substrates retain their conductivity even after being bent and unbent 200 times attributing to its embedded structure and the specific materials, while an indium tin oxide on synthetic plastic substrate lost its conductivity after the same amount of bending. These lightweight organic solar cells pave the way for future biodegradable and wearable electronics.