Evolution of favourable nanomorphology which can withstand external stimuli is a critical issue for efficient and stable organic solar cells. Here, we demonstrate a novel strategy for the stabilization of nanomorphology of organic solar cells by inducing polymeric nanowire network structures. Thermal annealing of poly(3- hexylthiophene-2,5-diyl) nanowires, highly crystalline, 1-dimensional structures held together through interchain π-π stacking, led to the formation of nanowire network structures confirmed through small angle neutron scattering measurements. The physically interconnected network structures form robust electron donor domains and impose confinement which suppresses the aggregation of the electron acceptor, [6,6]-phenyl-C61-butylric acid methyl ester. Organic solar cells having the nanowire network structures showed increased power conversion efficiencies and dramatically enhanced thermal stability compared to bulk heterojunction (BHJ) and non-network nanowire-based devices. Furthermore, the performance of the nanowire network-based devices was inversely related to the size of the networks, attesting to the significance of nanoconfined geometry formed within nanowire network structures.