Abstract: The invention provides a novel fabrication method to produce solar cells using water-based inks that can be readily used in roll-to-roll processing, ink-jet printing and other large-scale fabrication processes. The invention also provides OPV devices with significantly improved efficiency. The invention offers a number of advantages over existing methods: (1) use of water dispersions instead of environmentally hazardous organic solvents, (2) use of semiconducting nanoparticles that allow control of the domain size and structure, (3) treatment of PEDOT:PSS using UV/Ozone allows film uniformity from aqueoue dispersions, (4) use of heat-IR radiation to make uniform films, (5) use of hole-blocking layer for increased fill factors (squareness of the I-V curve, the ratio between the maximum power obtained and the maximum power obtainable defined by the open circuit voltage and the short circuit current).