Origin of the Reduced Fill Factor and Photocurrent in MDMO‐PPV:PCNEPV All‐Polymer Solar Cells

Abstract The photogeneration mechanism in blends of poly[2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4 ‐ phenylene vinylene] (MDMO‐PPV) and poly[oxa‐1,4‐phenylene‐(1‐cyano‐1,2‐vinylene)‐(2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylene)‐1,2‐(2‐cyanovinylene)‐1,4‐phenylene] (PCNEPV) is investigated. The photocurrent in the MDMO‐PPV:PCNEPV blends is strongly dependent on the applied voltage as a result of a low dissociation efficiency of the bound electron–hole pairs. The dissociation efficiency is limited by low carrier mobilities, low dielectric constant, and the strong intermixing of the polymers, leading to a low fill factor and a reduced photocurrent at operating conditions. Additionally, electrons trapped in the PCNEPV phase recombine with the mobile holes in the MDMO‐PPV phase at the interface between the two polymers, thereby affecting the open‐circuit voltage and increasing the recombination losses. At an intensity of one sun, Langevin recombination of mobile carriers dominates over trap‐assisted recombination.