The interest in organic solar cells (OSCs) has grown exponentially over the last few years and devices are approaching a symbolic power conversion efficiency (PCE) of 20%. However, many challenges related to scaling‐up several processes must be addressed before this technology can reach the production scale. In order to facilitate the scaled‐up production of OSCs, the synthesis of an efficient and cost‐effective conjugated polymer, PPDT2FBT, was adapted to a water‐based method of direct (hetero)arylation polymerization (DHAP). This aqueous DHAP method yields molecular weights (Mn) between 20 and 80 kg mol−1, which can be controlled by manipulating the polymerization time and temperature. The varying polymer molecular weights were used for the fabrication of OSCs with PC61BM and air‐processed in non‐halogenated solvents. When the 40 kg mol−1 PPDT2FBT:PC61BM active layer is slot‐die coated, PCEs of 8.15% were attained under standard one sun illumination. The temporal stability of the devices under constant illumination showed a 80% PCE loss after 220 hours (TS80), after the initial ‘‘burn‐in’’.

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