Solution-processed organic solar cells based on the bulk heterojunction PCE10:EH-IDTBR were fabricated (ITO|PEDOT:PSS|PCE10:EH-IDTBR|ZnO|Ag) . ITO-coated glass substrates (1.3 × 1.3 cm 2 ) were selectively etched with zinc dust and 2 M HCl, followed by thorough sonication in acetone, ethanol, isopropyl alcohol and deionised water. The cleaned substrates were then subjected to UV-Ozone treatment for 40 minutes (BioForce Nanosciences UV/Ozone ProCleaner). PEDOT:PSS was subsequently filtered through a Millex-GP 0.22 µm PES filter and spin-coated onto the ITO substrates at 4000 r.p.m. Further annealing on a hot plate in air at 383 K for 40 minutes yielded the final holetransport layer. To form the light-harvesting active layer, a solution of PCE10:EH-IDTBR (1:2 weight ratio, 24 mg ml -1 ) was prepared in chlorobenzene and spin-coated in a N2-filled glovebox at 3000 r.p.m. ZnO nanoparticles were then spin coated at 4000 r.p.m. to obtain the electron-transport layer. Finally, Ag (100 nm) was thermally evaporated through a patterned mask under vacuum (~10 -5 mbar), defining an active area of ~0.5 × 0.5 cm 2 for each device.