Title: Understanding and Controlling Charge Carrier Recombination in Organic Bulk Heterojunction Towards High-Efficiency Devices

Abstract: One key advantage of solution-processable organic semiconductors is the opportunity of blending different materials in order to attain novel material properties and applications. The concept of ternary blend organic solar cells makes use of exactly that idea: three (or more) organic chromophores are combined to better match the solar irradiance spectrum and thus increase the amount of light absorbed, which in turn will increase the power output of the solar cell. However, charge transport limitations of many current generation polymer blends typically require rather low active layer thicknesses (around 100 nm) for optimum performance.1 Here, we show the design of non-fullerene acceptor (NFA)2 and fullerene-based solar3,4 cells with reduced charge recombination processes leading to a high short circuit current density (Jsc) and fill factor (FF) in ternary blends, thus demonstrating how the recombination thresholds can be overcome.